diff --git a/tests/fixtures/sbml/ode_example_enzml.json b/tests/fixtures/sbml/ode_example_enzml.json
index 57a2b6e3..ca2dca0b 100644
--- a/tests/fixtures/sbml/ode_example_enzml.json
+++ b/tests/fixtures/sbml/ode_example_enzml.json
@@ -12,7 +12,7 @@
     "modified": "schema:dateModified",
     "creators": "schema:creator"
   },
-  "@id": "enzml:EnzymeMLDocument/44649453-a157-4cb7-be07-8fb09a82f4ca",
+  "@id": "enzml:EnzymeMLDocument/833d46aa-58c7-4d42-b341-43f1fe0fece0",
   "@type": [
     "enzml:EnzymeMLDocument"
   ],
@@ -32,7 +32,7 @@
         "name": "schema:name",
         "volume": "OBO:OBI_0002139"
       },
-      "@id": "enzml:Vessel/02063116-73f1-4ba1-b166-8fe835e55659",
+      "@id": "enzml:Vessel/abc02182-675a-4fd7-b067-9f376f17b874",
       "@type": [
         "enzml:Vessel",
         "OBO:OBI_0400081"
@@ -59,7 +59,7 @@
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "enzml:BaseUnit/efd21ea0-af02-4920-9036-9c8337cf0421",
+            "@id": "enzml:BaseUnit/7ea9c0d4-dcbb-4e59-94f2-7b1779e35b1b",
             "@type": [
               "enzml:BaseUnit"
             ],
@@ -96,7 +96,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:Protein/cf3097ad-5833-4ff8-99f1-784cd5f673ca",
+      "@id": "enzml:Protein/487be0d2-e325-4f0b-857b-3bd8d54c4003",
       "@type": [
         "enzml:Protein",
         "schema:Protein"
@@ -127,7 +127,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:Complex/fa79ccd6-acbe-47e4-a8d1-795eb18346db",
+      "@id": "enzml:Complex/2f52086d-d7a8-4a2d-870b-bd6bafd91504",
       "@type": [
         "enzml:Complex"
       ],
@@ -160,7 +160,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:SmallMolecule/5375d6fb-6246-43b0-bc81-d47e3e72493f",
+      "@id": "enzml:SmallMolecule/551e35d3-ae18-490d-b4a7-003fcd28f446",
       "@type": [
         "enzml:SmallMolecule"
       ],
@@ -191,7 +191,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:SmallMolecule/c7318d93-2a0f-44c0-9ebe-a79fc27bf01e",
+      "@id": "enzml:SmallMolecule/1a93b3f8-ce94-429d-975b-ff6a837b0424",
       "@type": [
         "enzml:SmallMolecule"
       ],
@@ -219,7 +219,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:Measurement/ef303c49-7554-4367-9f44-cb6e9838c1be",
+      "@id": "enzml:Measurement/83db3a41-626e-461b-80d2-9618997c6af3",
       "@type": [
         "enzml:Measurement"
       ],
@@ -235,7 +235,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:MeasurementData/3beaeb28-72a4-4398-ae34-c9208c03aa0b",
+          "@id": "enzml:MeasurementData/a1e71511-2b64-40af-a50f-7ede47b45baa",
           "@type": [
             "enzml:MeasurementData"
           ],
@@ -260,7 +260,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/cff3e0ad-ce88-479a-8c01-b06e012e3195",
+                "@id": "enzml:BaseUnit/0a98675d-d6e6-4551-8f2a-90483c57936d",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -274,7 +274,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/df1eed89-6a35-483e-a187-b981d9ee0405",
+                "@id": "enzml:BaseUnit/335f309c-13e0-4eb8-9765-3945a8683f7f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -303,12 +303,12 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/634613e6-a06f-42e9-9e11-b32c3e6f6f09",
+                "@id": "enzml:BaseUnit/4e3a6a14-ca74-4c8a-b00f-45a3cfea6e11",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
                 "kind": "second",
-                "exponent": -1,
+                "exponent": 1,
                 "scale": 1.0
               }
             ]
@@ -351,7 +351,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:MeasurementData/00c0dabc-47cc-40d5-a4d5-7809880aad52",
+          "@id": "enzml:MeasurementData/9de1a9fe-ede0-4e0b-a8cc-84e8dce6cb57",
           "@type": [
             "enzml:MeasurementData"
           ],
@@ -376,7 +376,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/cff3e0ad-ce88-479a-8c01-b06e012e3195",
+                "@id": "enzml:BaseUnit/0a98675d-d6e6-4551-8f2a-90483c57936d",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -390,7 +390,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/df1eed89-6a35-483e-a187-b981d9ee0405",
+                "@id": "enzml:BaseUnit/335f309c-13e0-4eb8-9765-3945a8683f7f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -419,12 +419,12 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/634613e6-a06f-42e9-9e11-b32c3e6f6f09",
+                "@id": "enzml:BaseUnit/4e3a6a14-ca74-4c8a-b00f-45a3cfea6e11",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
                 "kind": "second",
-                "exponent": -1,
+                "exponent": 1,
                 "scale": 1.0
               }
             ]
@@ -480,7 +480,7 @@
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "enzml:BaseUnit/83915bc7-e2b4-450f-b363-20eb027d1f3d",
+            "@id": "enzml:BaseUnit/31d5028b-2d30-4053-87e7-00b42a40b165",
             "@type": [
               "enzml:BaseUnit"
             ],
@@ -504,7 +504,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:Measurement/28bb1de1-4cd9-45e2-b160-3a2dd5ce3e34",
+      "@id": "enzml:Measurement/f7603279-9db3-4039-b501-97fee1f05c4b",
       "@type": [
         "enzml:Measurement"
       ],
@@ -520,7 +520,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:MeasurementData/24b00355-6bad-4771-a0e5-e65c7560b3a9",
+          "@id": "enzml:MeasurementData/f8d7f530-1f92-4cd7-b460-54b9cb03678b",
           "@type": [
             "enzml:MeasurementData"
           ],
@@ -545,7 +545,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/cff3e0ad-ce88-479a-8c01-b06e012e3195",
+                "@id": "enzml:BaseUnit/0a98675d-d6e6-4551-8f2a-90483c57936d",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -559,7 +559,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/df1eed89-6a35-483e-a187-b981d9ee0405",
+                "@id": "enzml:BaseUnit/335f309c-13e0-4eb8-9765-3945a8683f7f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -588,12 +588,12 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/634613e6-a06f-42e9-9e11-b32c3e6f6f09",
+                "@id": "enzml:BaseUnit/4e3a6a14-ca74-4c8a-b00f-45a3cfea6e11",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
                 "kind": "second",
-                "exponent": -1,
+                "exponent": 1,
                 "scale": 1.0
               }
             ]
@@ -636,7 +636,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:MeasurementData/405dfbaf-cc21-41d4-836d-fdadc1d0c1b3",
+          "@id": "enzml:MeasurementData/828564ec-ec24-42c2-98b2-115fdc1f2a3c",
           "@type": [
             "enzml:MeasurementData"
           ],
@@ -661,7 +661,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/cff3e0ad-ce88-479a-8c01-b06e012e3195",
+                "@id": "enzml:BaseUnit/0a98675d-d6e6-4551-8f2a-90483c57936d",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -675,7 +675,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/df1eed89-6a35-483e-a187-b981d9ee0405",
+                "@id": "enzml:BaseUnit/335f309c-13e0-4eb8-9765-3945a8683f7f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -704,12 +704,12 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/634613e6-a06f-42e9-9e11-b32c3e6f6f09",
+                "@id": "enzml:BaseUnit/4e3a6a14-ca74-4c8a-b00f-45a3cfea6e11",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
                 "kind": "second",
-                "exponent": -1,
+                "exponent": 1,
                 "scale": 1.0
               }
             ]
@@ -765,7 +765,7 @@
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "enzml:BaseUnit/83915bc7-e2b4-450f-b363-20eb027d1f3d",
+            "@id": "enzml:BaseUnit/31d5028b-2d30-4053-87e7-00b42a40b165",
             "@type": [
               "enzml:BaseUnit"
             ],
@@ -787,23 +787,80 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:Equation/87c7fc6d-6933-42be-a33a-c8eecb5901b7",
+      "@id": "enzml:Equation/69aec529-07bc-447a-8169-a20dc623c81a",
       "@type": [
         "enzml:Equation"
       ],
-      "equation": "E_tot*kcat*s0/(K_m + s0)",
+      "equation": "E_tot * kcat * s0 / (K_m + s0)",
+      "equation_type": "ode",
+      "species_id": "s1",
+      "variables": [
+        {
+          "@context": {
+            "enzml": "http://www.enzymeml.org/v2/",
+            "OBO": "http://purl.obolibrary.org/obo/",
+            "schema": "https://schema.org/",
+            "id": "schema:identifier"
+          },
+          "@id": "enzml:Variable/b4d171e6-c5ee-416b-859f-6560c5f18b5d",
+          "@type": [
+            "enzml:Variable"
+          ],
+          "id": "s0",
+          "name": "s0",
+          "symbol": "s0"
+        }
+      ]
+    },
+    {
+      "@context": {
+        "enzml": "http://www.enzymeml.org/v2/",
+        "OBO": "http://purl.obolibrary.org/obo/",
+        "schema": "https://schema.org/",
+        "species_id": {
+          "@type": "@id"
+        }
+      },
+      "@id": "enzml:Equation/e1e66a46-8111-4003-9eeb-f163081c2e96",
+      "@type": [
+        "enzml:Equation"
+      ],
+      "equation": "100",
+      "equation_type": "initialAssignment",
+      "species_id": "E_tot",
+      "variables": []
+    }
+  ],
+  "parameters": [
+    {
+      "@context": {
+        "enzml": "http://www.enzymeml.org/v2/",
+        "OBO": "http://purl.obolibrary.org/obo/",
+        "schema": "https://schema.org/",
+        "id": {
+          "@id": "schema:identifier",
+          "@type": "@id"
+        }
+      },
+      "@id": "enzml:Parameter/2872b6d6-191f-4bc4-a36a-130eb4534837",
+      "@type": [
+        "enzml:Parameter"
+      ],
+      "id": "kcat",
+      "name": "kcat",
+      "symbol": "kcat",
       "unit": {
         "@context": {
           "enzml": "http://www.enzymeml.org/v2/",
           "OBO": "http://purl.obolibrary.org/obo/",
           "schema": "https://schema.org/"
         },
-        "@id": "OBO:UO_0000063",
+        "@id": "OBO:UO_0000010",
         "@type": [
           "OBO:UO_0000000"
         ],
         "id": "u4",
-        "name": "mmol / l s",
+        "name": "1 / s",
         "base_units": [
           {
             "@context": {
@@ -811,35 +868,7 @@
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "enzml:BaseUnit/cff3e0ad-ce88-479a-8c01-b06e012e3195",
-            "@type": [
-              "enzml:BaseUnit"
-            ],
-            "kind": "mole",
-            "exponent": 1,
-            "scale": -3.0
-          },
-          {
-            "@context": {
-              "enzml": "http://www.enzymeml.org/v2/",
-              "OBO": "http://purl.obolibrary.org/obo/",
-              "schema": "https://schema.org/"
-            },
-            "@id": "enzml:BaseUnit/df1eed89-6a35-483e-a187-b981d9ee0405",
-            "@type": [
-              "enzml:BaseUnit"
-            ],
-            "kind": "litre",
-            "exponent": -1,
-            "scale": 1.0
-          },
-          {
-            "@context": {
-              "enzml": "http://www.enzymeml.org/v2/",
-              "OBO": "http://purl.obolibrary.org/obo/",
-              "schema": "https://schema.org/"
-            },
-            "@id": "enzml:BaseUnit/634613e6-a06f-42e9-9e11-b32c3e6f6f09",
+            "@id": "enzml:BaseUnit/4e3a6a14-ca74-4c8a-b00f-45a3cfea6e11",
             "@type": [
               "enzml:BaseUnit"
             ],
@@ -849,223 +878,93 @@
           }
         ]
       },
-      "equation_type": "ode",
-      "species_id": "s1",
-      "variables": [
-        {
-          "@context": {
-            "enzml": "http://www.enzymeml.org/v2/",
-            "OBO": "http://purl.obolibrary.org/obo/",
-            "schema": "https://schema.org/",
-            "id": "schema:identifier"
-          },
-          "@id": "enzml:Variable/49c819d7-0f8a-4d2e-9a82-09cf62d48aad",
-          "@type": [
-            "enzml:Variable"
-          ],
-          "id": "s0",
-          "name": "s0",
-          "symbol": "s0"
+      "upper": 100.0,
+      "lower": 0.0,
+      "stderr": 0.1,
+      "constant": true
+    },
+    {
+      "@context": {
+        "enzml": "http://www.enzymeml.org/v2/",
+        "OBO": "http://purl.obolibrary.org/obo/",
+        "schema": "https://schema.org/",
+        "id": {
+          "@id": "schema:identifier",
+          "@type": "@id"
         }
+      },
+      "@id": "enzml:Parameter/31e315d7-8e87-4ef9-9ca4-1e9e08f2ded7",
+      "@type": [
+        "enzml:Parameter"
       ],
-      "parameters": [
-        {
-          "@context": {
-            "enzml": "http://www.enzymeml.org/v2/",
-            "OBO": "http://purl.obolibrary.org/obo/",
-            "schema": "https://schema.org/",
-            "id": {
-              "@id": "schema:identifier",
-              "@type": "@id"
-            }
-          },
-          "@id": "enzml:Parameter/404206dc-7e11-432e-b1a8-871b822325ef",
-          "@type": [
-            "enzml:Parameter"
-          ],
-          "id": "kcat",
-          "name": "kcat",
-          "symbol": "kcat",
-          "unit": {
-            "@context": {
-              "enzml": "http://www.enzymeml.org/v2/",
-              "OBO": "http://purl.obolibrary.org/obo/",
-              "schema": "https://schema.org/"
-            },
-            "@id": "OBO:UO_0000010",
-            "@type": [
-              "OBO:UO_0000000"
-            ],
-            "id": "u5",
-            "name": "1 / s",
-            "base_units": [
-              {
-                "@context": {
-                  "enzml": "http://www.enzymeml.org/v2/",
-                  "OBO": "http://purl.obolibrary.org/obo/",
-                  "schema": "https://schema.org/"
-                },
-                "@id": "enzml:BaseUnit/634613e6-a06f-42e9-9e11-b32c3e6f6f09",
-                "@type": [
-                  "enzml:BaseUnit"
-                ],
-                "kind": "second",
-                "exponent": -1,
-                "scale": 1.0
-              }
-            ]
-          },
-          "upper": 100.0,
-          "lower": 0.0,
-          "stderr": 0.1,
-          "constant": true
+      "id": "K_m",
+      "name": "K_m",
+      "symbol": "K_m",
+      "unit": {
+        "@context": {
+          "enzml": "http://www.enzymeml.org/v2/",
+          "OBO": "http://purl.obolibrary.org/obo/",
+          "schema": "https://schema.org/"
         },
-        {
-          "@context": {
-            "enzml": "http://www.enzymeml.org/v2/",
-            "OBO": "http://purl.obolibrary.org/obo/",
-            "schema": "https://schema.org/",
-            "id": {
-              "@id": "schema:identifier",
-              "@type": "@id"
-            }
-          },
-          "@id": "enzml:Parameter/a5b7ca60-4945-4cfe-9eb9-6c97dfdaa770",
-          "@type": [
-            "enzml:Parameter"
-          ],
-          "id": "K_m",
-          "name": "K_m",
-          "symbol": "K_m",
-          "unit": {
+        "@id": "OBO:UO_0000063",
+        "@type": [
+          "OBO:UO_0000000"
+        ],
+        "id": "u2",
+        "name": "mmol / l",
+        "base_units": [
+          {
             "@context": {
               "enzml": "http://www.enzymeml.org/v2/",
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "OBO:UO_0000063",
+            "@id": "enzml:BaseUnit/0a98675d-d6e6-4551-8f2a-90483c57936d",
             "@type": [
-              "OBO:UO_0000000"
+              "enzml:BaseUnit"
             ],
-            "id": "u2",
-            "name": "mmol / l",
-            "base_units": [
-              {
-                "@context": {
-                  "enzml": "http://www.enzymeml.org/v2/",
-                  "OBO": "http://purl.obolibrary.org/obo/",
-                  "schema": "https://schema.org/"
-                },
-                "@id": "enzml:BaseUnit/cff3e0ad-ce88-479a-8c01-b06e012e3195",
-                "@type": [
-                  "enzml:BaseUnit"
-                ],
-                "kind": "mole",
-                "exponent": 1,
-                "scale": -3.0
-              },
-              {
-                "@context": {
-                  "enzml": "http://www.enzymeml.org/v2/",
-                  "OBO": "http://purl.obolibrary.org/obo/",
-                  "schema": "https://schema.org/"
-                },
-                "@id": "enzml:BaseUnit/df1eed89-6a35-483e-a187-b981d9ee0405",
-                "@type": [
-                  "enzml:BaseUnit"
-                ],
-                "kind": "litre",
-                "exponent": -1,
-                "scale": 1.0
-              }
-            ]
-          },
-          "upper": 100.0,
-          "lower": 0.0,
-          "stderr": 0.1,
-          "constant": true
-        },
-        {
-          "@context": {
-            "enzml": "http://www.enzymeml.org/v2/",
-            "OBO": "http://purl.obolibrary.org/obo/",
-            "schema": "https://schema.org/",
-            "id": {
-              "@id": "schema:identifier",
-              "@type": "@id"
-            }
+            "kind": "mole",
+            "exponent": 1,
+            "scale": -3.0
           },
-          "@id": "enzml:Parameter/26b501d3-7200-4813-ac11-b62f0f665054",
-          "@type": [
-            "enzml:Parameter"
-          ],
-          "id": "E_tot",
-          "name": "E_tot",
-          "symbol": "E_tot",
-          "unit": {
+          {
             "@context": {
               "enzml": "http://www.enzymeml.org/v2/",
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "OBO:UO_0000063",
+            "@id": "enzml:BaseUnit/335f309c-13e0-4eb8-9765-3945a8683f7f",
             "@type": [
-              "OBO:UO_0000000"
+              "enzml:BaseUnit"
             ],
-            "id": "u2",
-            "name": "mmol / l",
-            "base_units": [
-              {
-                "@context": {
-                  "enzml": "http://www.enzymeml.org/v2/",
-                  "OBO": "http://purl.obolibrary.org/obo/",
-                  "schema": "https://schema.org/"
-                },
-                "@id": "enzml:BaseUnit/cff3e0ad-ce88-479a-8c01-b06e012e3195",
-                "@type": [
-                  "enzml:BaseUnit"
-                ],
-                "kind": "mole",
-                "exponent": 1,
-                "scale": -3.0
-              },
-              {
-                "@context": {
-                  "enzml": "http://www.enzymeml.org/v2/",
-                  "OBO": "http://purl.obolibrary.org/obo/",
-                  "schema": "https://schema.org/"
-                },
-                "@id": "enzml:BaseUnit/df1eed89-6a35-483e-a187-b981d9ee0405",
-                "@type": [
-                  "enzml:BaseUnit"
-                ],
-                "kind": "litre",
-                "exponent": -1,
-                "scale": 1.0
-              }
-            ]
-          },
-          "upper": 100.0,
-          "lower": 0.0,
-          "stderr": 0.1,
-          "constant": true
-        }
-      ]
+            "kind": "litre",
+            "exponent": -1,
+            "scale": 1.0
+          }
+        ]
+      },
+      "upper": 100.0,
+      "lower": 0.0,
+      "stderr": 0.1,
+      "constant": true
     },
     {
       "@context": {
         "enzml": "http://www.enzymeml.org/v2/",
         "OBO": "http://purl.obolibrary.org/obo/",
         "schema": "https://schema.org/",
-        "species_id": {
+        "id": {
+          "@id": "schema:identifier",
           "@type": "@id"
         }
       },
-      "@id": "enzml:Equation/3991effb-6394-4b6d-baa8-a06462e2101f",
+      "@id": "enzml:Parameter/d49325e0-8483-469a-9d6d-1bcadac2bb98",
       "@type": [
-        "enzml:Equation"
+        "enzml:Parameter"
       ],
-      "equation": "100",
+      "id": "E_tot",
+      "name": "E_tot",
+      "symbol": "E_tot",
       "unit": {
         "@context": {
           "enzml": "http://www.enzymeml.org/v2/",
@@ -1085,7 +984,7 @@
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "enzml:BaseUnit/cff3e0ad-ce88-479a-8c01-b06e012e3195",
+            "@id": "enzml:BaseUnit/0a98675d-d6e6-4551-8f2a-90483c57936d",
             "@type": [
               "enzml:BaseUnit"
             ],
@@ -1099,7 +998,7 @@
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "enzml:BaseUnit/df1eed89-6a35-483e-a187-b981d9ee0405",
+            "@id": "enzml:BaseUnit/335f309c-13e0-4eb8-9765-3945a8683f7f",
             "@type": [
               "enzml:BaseUnit"
             ],
@@ -1109,10 +1008,10 @@
           }
         ]
       },
-      "equation_type": "initialAssignment",
-      "species_id": "E_tot",
-      "variables": [],
-      "parameters": []
+      "upper": 100.0,
+      "lower": 0.0,
+      "stderr": 0.1,
+      "constant": true
     }
   ]
 }
\ No newline at end of file
diff --git a/tests/fixtures/sbml/ode_example_sbml.xml b/tests/fixtures/sbml/ode_example_sbml.xml
index 7d4ca6b1..dc3baf8c 100644
--- a/tests/fixtures/sbml/ode_example_sbml.xml
+++ b/tests/fixtures/sbml/ode_example_sbml.xml
@@ -2,22 +2,22 @@
 <sbml xmlns="http://www.sbml.org/sbml/level3/version2/core" level="3" version="2">
     <model name="Test">
         <annotation>
-            <enzymeml:data xmlns:enzymeml="https://www.enzymeml.org/v2" file="data.csv">
+            <enzymeml:data xmlns:enzymeml="https://www.enzymeml.org/v2" file="data.tsv">
                 <enzymeml:measurement id="m0" name="m0" timeUnit="u1">
                     <enzymeml:conditions>
                         <enzymeml:ph value="7.0"/>
                         <enzymeml:temperature value="298.15" unit="u3"/>
                     </enzymeml:conditions>
-                    <enzymeml:initConc species="s0" unit="u2"/>
-                    <enzymeml:initConc species="s1" value="10.0" unit="u2"/>
+                    <enzymeml:speciesData species="s0" unit="u2" type="CONCENTRATION"/>
+                    <enzymeml:speciesData species="s1" value="10.0" unit="u2" type="CONCENTRATION"/>
                 </enzymeml:measurement>
                 <enzymeml:measurement id="m1" name="m1" timeUnit="u1">
                     <enzymeml:conditions>
                         <enzymeml:ph value="7.0"/>
                         <enzymeml:temperature value="298.15" unit="u3"/>
                     </enzymeml:conditions>
-                    <enzymeml:initConc species="s0" unit="u2"/>
-                    <enzymeml:initConc species="s1" value="10.0" unit="u2"/>
+                    <enzymeml:speciesData species="s0" unit="u2" type="CONCENTRATION"/>
+                    <enzymeml:speciesData species="s1" value="10.0" unit="u2" type="CONCENTRATION"/>
                 </enzymeml:measurement>
             </enzymeml:data>
         </annotation>
@@ -56,7 +56,7 @@
                     </rdf:RDF>
                 </annotation>
                 <listOfUnits>
-                    <unit kind="second" exponent="-1" scale="1"/>
+                    <unit kind="second" exponent="1" scale="1"/>
                 </listOfUnits>
             </unitDefinition>
             <unitDefinition id="u3" name="K">
@@ -71,21 +71,7 @@
                     <unit kind="kelvin" exponent="1" scale="1"/>
                 </listOfUnits>
             </unitDefinition>
-            <unitDefinition id="u4" name="mmol / l s">
-                <annotation>
-                    <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
-                        <rdf:Description rdf:about="http://purl.obolibrary.org/obo/UO_0000063">
-                            <rdf:type rdf:resource="http://purl.obolibrary.org/obo/UO_0000000"/>
-                        </rdf:Description>
-                    </rdf:RDF>
-                </annotation>
-                <listOfUnits>
-                    <unit kind="mole" exponent="1" scale="-3"/>
-                    <unit kind="litre" exponent="-1" scale="1"/>
-                    <unit kind="second" exponent="-1" scale="1"/>
-                </listOfUnits>
-            </unitDefinition>
-            <unitDefinition id="u5" name="1 / s">
+            <unitDefinition id="u4" name="1 / s">
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
                         <rdf:Description rdf:about="http://purl.obolibrary.org/obo/UO_0000010">
@@ -104,7 +90,7 @@
                     <rdf:RDF xmlns:OBO="http://purl.obolibrary.org/obo/"
                              xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:schema="https://schema.org/">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Vessel/02063116-73f1-4ba1-b166-8fe835e55659">
+                                rdf:about="http://www.enzymeml.org/v2/Vessel/abc02182-675a-4fd7-b067-9f376f17b874">
                             <schema:name>Vessel 1</schema:name>
                             <OBO:OBI_0002139 rdf:datatype="http://www.w3.org/2001/XMLSchema#double">10.0
                             </OBO:OBI_0002139>
@@ -121,7 +107,7 @@
                     <rdf:RDF xmlns:OBO="http://purl.obolibrary.org/obo/"
                              xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:schema="https://schema.org/">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Protein/cf3097ad-5833-4ff8-99f1-784cd5f673ca">
+                                rdf:about="http://www.enzymeml.org/v2/Protein/487be0d2-e325-4f0b-857b-3bd8d54c4003">
                             <schema:name>Enzyme</schema:name>
                             <OBO:GSSO_007262>MTEY</OBO:GSSO_007262>
                             <OBO:OBI_0100026>E.coli</OBO:OBI_0100026>
@@ -141,7 +127,7 @@
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:schema="https://schema.org/">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Complex/fa79ccd6-acbe-47e4-a8d1-795eb18346db">
+                                rdf:about="http://www.enzymeml.org/v2/Complex/2f52086d-d7a8-4a2d-870b-bd6bafd91504">
                             <schema:name>Enzyme-Substrate Complex</schema:name>
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/Complex"/>
                         </rdf:Description>
@@ -157,7 +143,7 @@
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:schema="https://schema.org/">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/SmallMolecule/5375d6fb-6246-43b0-bc81-d47e3e72493f">
+                                rdf:about="http://www.enzymeml.org/v2/SmallMolecule/551e35d3-ae18-490d-b4a7-003fcd28f446">
                             <schema:name>Substrate</schema:name>
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/SmallMolecule"/>
                         </rdf:Description>
@@ -173,7 +159,7 @@
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:schema="https://schema.org/">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/SmallMolecule/c7318d93-2a0f-44c0-9ebe-a79fc27bf01e">
+                                rdf:about="http://www.enzymeml.org/v2/SmallMolecule/1a93b3f8-ce94-429d-975b-ff6a837b0424">
                             <schema:name>Product</schema:name>
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/SmallMolecule"/>
                         </rdf:Description>
@@ -186,11 +172,11 @@
             </species>
         </listOfSpecies>
         <listOfParameters>
-            <parameter id="kcat" name="kcat" units="u5" constant="true">
+            <parameter id="kcat" name="kcat" units="u4" constant="true">
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Parameter/404206dc-7e11-432e-b1a8-871b822325ef">
+                                rdf:about="http://www.enzymeml.org/v2/Parameter/2872b6d6-191f-4bc4-a36a-130eb4534837">
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/Parameter"/>
                         </rdf:Description>
                     </rdf:RDF>
@@ -205,7 +191,7 @@
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Parameter/a5b7ca60-4945-4cfe-9eb9-6c97dfdaa770">
+                                rdf:about="http://www.enzymeml.org/v2/Parameter/31e315d7-8e87-4ef9-9ca4-1e9e08f2ded7">
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/Parameter"/>
                         </rdf:Description>
                     </rdf:RDF>
@@ -220,7 +206,7 @@
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Parameter/26b501d3-7200-4813-ac11-b62f0f665054">
+                                rdf:about="http://www.enzymeml.org/v2/Parameter/d49325e0-8483-469a-9d6d-1bcadac2bb98">
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/Parameter"/>
                         </rdf:Description>
                     </rdf:RDF>
diff --git a/tests/fixtures/sbml/odes_example.omex b/tests/fixtures/sbml/odes_example.omex
new file mode 100644
index 00000000..087704de
Binary files /dev/null and b/tests/fixtures/sbml/odes_example.omex differ
diff --git a/tests/fixtures/sbml/reaction_example_enzml.json b/tests/fixtures/sbml/reaction_example_enzml.json
index 7e01e7f9..b264df26 100644
--- a/tests/fixtures/sbml/reaction_example_enzml.json
+++ b/tests/fixtures/sbml/reaction_example_enzml.json
@@ -12,7 +12,7 @@
     "modified": "schema:dateModified",
     "creators": "schema:creator"
   },
-  "@id": "enzml:EnzymeMLDocument/b8426986-8c86-43f9-a03e-efbc1577d70a",
+  "@id": "enzml:EnzymeMLDocument/0dd4f410-0464-451f-ae3f-a45d11b7c181",
   "@type": [
     "enzml:EnzymeMLDocument"
   ],
@@ -32,7 +32,7 @@
         "name": "schema:name",
         "volume": "OBO:OBI_0002139"
       },
-      "@id": "enzml:Vessel/e594aa18-c317-4e87-b68f-ca7337c910d0",
+      "@id": "enzml:Vessel/a2ea41db-032c-4a61-a7d5-254137d0bce9",
       "@type": [
         "enzml:Vessel",
         "OBO:OBI_0400081"
@@ -59,7 +59,7 @@
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "enzml:BaseUnit/26d67db7-127b-4bf5-8578-dfc75ec003d8",
+            "@id": "enzml:BaseUnit/c64d956a-7d88-4886-8c05-8f2458178c0f",
             "@type": [
               "enzml:BaseUnit"
             ],
@@ -96,7 +96,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:Protein/de66507f-620a-42ee-9162-7401630cc4bc",
+      "@id": "enzml:Protein/42828d0d-f4ac-489b-acd5-cd74c080f340",
       "@type": [
         "enzml:Protein",
         "schema:Protein"
@@ -130,7 +130,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:SmallMolecule/210850a2-7071-4594-9762-d0520bd2ded6",
+      "@id": "enzml:SmallMolecule/e794f30d-51ea-4b89-a5d7-555bcd70efe5",
       "@type": [
         "enzml:SmallMolecule"
       ],
@@ -159,7 +159,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:SmallMolecule/5f11bcce-405f-4b0e-9a58-7e812c80fcc5",
+      "@id": "enzml:SmallMolecule/4b8a1f78-1874-447a-aee7-a80970bb1301",
       "@type": [
         "enzml:SmallMolecule"
       ],
@@ -184,7 +184,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:Reaction/e236d1d1-c83a-45bb-859a-51bd15cee184",
+      "@id": "enzml:Reaction/d62c8122-e540-441b-97b5-87ed786d61ff",
       "@type": [
         "enzml:Reaction"
       ],
@@ -200,68 +200,11 @@
             "@type": "@id"
           }
         },
-        "@id": "enzml:Equation/deb8cae4-181a-47de-b5c5-282fdabd69d6",
+        "@id": "enzml:Equation/f9c5b6d8-e3df-4caa-8c09-cdaf433bf964",
         "@type": [
           "enzml:Equation"
         ],
-        "equation": "kcat*p0*s0/(K_m + s0)",
-        "unit": {
-          "@context": {
-            "enzml": "http://www.enzymeml.org/v2/",
-            "OBO": "http://purl.obolibrary.org/obo/",
-            "schema": "https://schema.org/"
-          },
-          "@id": "OBO:UO_0000063",
-          "@type": [
-            "OBO:UO_0000000"
-          ],
-          "id": "u1",
-          "name": "mmol / l s",
-          "base_units": [
-            {
-              "@context": {
-                "enzml": "http://www.enzymeml.org/v2/",
-                "OBO": "http://purl.obolibrary.org/obo/",
-                "schema": "https://schema.org/"
-              },
-              "@id": "enzml:BaseUnit/801b612f-9b16-4030-bc53-20e00d9e525b",
-              "@type": [
-                "enzml:BaseUnit"
-              ],
-              "kind": "mole",
-              "exponent": 1,
-              "scale": -3.0
-            },
-            {
-              "@context": {
-                "enzml": "http://www.enzymeml.org/v2/",
-                "OBO": "http://purl.obolibrary.org/obo/",
-                "schema": "https://schema.org/"
-              },
-              "@id": "enzml:BaseUnit/8c63ea70-d26e-45e4-beef-651da82864d0",
-              "@type": [
-                "enzml:BaseUnit"
-              ],
-              "kind": "litre",
-              "exponent": -1,
-              "scale": 1.0
-            },
-            {
-              "@context": {
-                "enzml": "http://www.enzymeml.org/v2/",
-                "OBO": "http://purl.obolibrary.org/obo/",
-                "schema": "https://schema.org/"
-              },
-              "@id": "enzml:BaseUnit/ec7aa14e-db13-4b05-ac2a-19973ff83e5a",
-              "@type": [
-                "enzml:BaseUnit"
-              ],
-              "kind": "second",
-              "exponent": -1,
-              "scale": 1.0
-            }
-          ]
-        },
+        "equation": "kcat * p0 * s0 / (K_m + s0)",
         "equation_type": "rateLaw",
         "variables": [
           {
@@ -271,7 +214,7 @@
               "schema": "https://schema.org/",
               "id": "schema:identifier"
             },
-            "@id": "enzml:Variable/2805b7f6-e844-422f-ac91-d7a9fbb3c98e",
+            "@id": "enzml:Variable/e8925678-42a3-4ae9-b6b0-1acf57e931fe",
             "@type": [
               "enzml:Variable"
             ],
@@ -286,7 +229,7 @@
               "schema": "https://schema.org/",
               "id": "schema:identifier"
             },
-            "@id": "enzml:Variable/9ee004f8-07ca-45b6-a1e8-4583c4e86fe7",
+            "@id": "enzml:Variable/f92597cf-ca5d-4287-83fb-d37e10f6bcf2",
             "@type": [
               "enzml:Variable"
             ],
@@ -294,124 +237,6 @@
             "name": "s0",
             "symbol": "s0"
           }
-        ],
-        "parameters": [
-          {
-            "@context": {
-              "enzml": "http://www.enzymeml.org/v2/",
-              "OBO": "http://purl.obolibrary.org/obo/",
-              "schema": "https://schema.org/",
-              "id": {
-                "@id": "schema:identifier",
-                "@type": "@id"
-              }
-            },
-            "@id": "enzml:Parameter/6b315b1b-26df-41a6-8a4f-1fc508e92a61",
-            "@type": [
-              "enzml:Parameter"
-            ],
-            "id": "K_m",
-            "name": "K_m",
-            "symbol": "K_m",
-            "unit": {
-              "@context": {
-                "enzml": "http://www.enzymeml.org/v2/",
-                "OBO": "http://purl.obolibrary.org/obo/",
-                "schema": "https://schema.org/"
-              },
-              "@id": "OBO:UO_0000063",
-              "@type": [
-                "OBO:UO_0000000"
-              ],
-              "id": "u2",
-              "name": "mmol / l",
-              "base_units": [
-                {
-                  "@context": {
-                    "enzml": "http://www.enzymeml.org/v2/",
-                    "OBO": "http://purl.obolibrary.org/obo/",
-                    "schema": "https://schema.org/"
-                  },
-                  "@id": "enzml:BaseUnit/801b612f-9b16-4030-bc53-20e00d9e525b",
-                  "@type": [
-                    "enzml:BaseUnit"
-                  ],
-                  "kind": "mole",
-                  "exponent": 1,
-                  "scale": -3.0
-                },
-                {
-                  "@context": {
-                    "enzml": "http://www.enzymeml.org/v2/",
-                    "OBO": "http://purl.obolibrary.org/obo/",
-                    "schema": "https://schema.org/"
-                  },
-                  "@id": "enzml:BaseUnit/8c63ea70-d26e-45e4-beef-651da82864d0",
-                  "@type": [
-                    "enzml:BaseUnit"
-                  ],
-                  "kind": "litre",
-                  "exponent": -1,
-                  "scale": 1.0
-                }
-              ]
-            },
-            "upper": 100.0,
-            "lower": 0.0,
-            "stderr": 0.1,
-            "constant": true
-          },
-          {
-            "@context": {
-              "enzml": "http://www.enzymeml.org/v2/",
-              "OBO": "http://purl.obolibrary.org/obo/",
-              "schema": "https://schema.org/",
-              "id": {
-                "@id": "schema:identifier",
-                "@type": "@id"
-              }
-            },
-            "@id": "enzml:Parameter/6619c640-3bbc-4b9d-b1e5-22665776bdaf",
-            "@type": [
-              "enzml:Parameter"
-            ],
-            "id": "kcat",
-            "name": "kcat",
-            "symbol": "kcat",
-            "unit": {
-              "@context": {
-                "enzml": "http://www.enzymeml.org/v2/",
-                "OBO": "http://purl.obolibrary.org/obo/",
-                "schema": "https://schema.org/"
-              },
-              "@id": "OBO:UO_0000010",
-              "@type": [
-                "OBO:UO_0000000"
-              ],
-              "id": "u3",
-              "name": "1 / s",
-              "base_units": [
-                {
-                  "@context": {
-                    "enzml": "http://www.enzymeml.org/v2/",
-                    "OBO": "http://purl.obolibrary.org/obo/",
-                    "schema": "https://schema.org/"
-                  },
-                  "@id": "enzml:BaseUnit/ec7aa14e-db13-4b05-ac2a-19973ff83e5a",
-                  "@type": [
-                    "enzml:BaseUnit"
-                  ],
-                  "kind": "second",
-                  "exponent": -1,
-                  "scale": 1.0
-                }
-              ]
-            },
-            "upper": 100.0,
-            "lower": 0.0,
-            "stderr": 0.1,
-            "constant": true
-          }
         ]
       },
       "species": [
@@ -424,7 +249,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:ReactionElement/d709628a-f70c-48bf-b2ae-33fe2a13b310",
+          "@id": "enzml:ReactionElement/64a1ab7c-7a6b-4479-afa4-a5732d1149c3",
           "@type": [
             "enzml:ReactionElement"
           ],
@@ -440,7 +265,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:ReactionElement/5286412a-e094-4a49-8cb9-e9e8e6c0ade4",
+          "@id": "enzml:ReactionElement/58c5315f-c835-46df-afb6-309aa61925c6",
           "@type": [
             "enzml:ReactionElement"
           ],
@@ -467,7 +292,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:Measurement/f4a6a78a-50eb-4850-b0e8-80b4155b75f2",
+      "@id": "enzml:Measurement/fee8c4cb-a15f-4ee4-b7c7-bcb9cf54ed6f",
       "@type": [
         "enzml:Measurement"
       ],
@@ -483,7 +308,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:MeasurementData/9d071dc1-70a5-4c78-bbe0-5fd5e8fad74f",
+          "@id": "enzml:MeasurementData/face315a-fd44-4b49-9f1d-0522b22aa073",
           "@type": [
             "enzml:MeasurementData"
           ],
@@ -499,7 +324,7 @@
             "@type": [
               "OBO:UO_0000000"
             ],
-            "id": "u2",
+            "id": "u1",
             "name": "mmol / l",
             "base_units": [
               {
@@ -508,7 +333,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/801b612f-9b16-4030-bc53-20e00d9e525b",
+                "@id": "enzml:BaseUnit/040c4b08-0af8-41d5-b3b6-0fa479ece06f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -522,7 +347,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/8c63ea70-d26e-45e4-beef-651da82864d0",
+                "@id": "enzml:BaseUnit/5069824d-7d9b-4afd-860d-232049d5fe2f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -542,7 +367,7 @@
             "@type": [
               "OBO:UO_0000000"
             ],
-            "id": "u4",
+            "id": "u2",
             "name": "s",
             "base_units": [
               {
@@ -551,12 +376,12 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/ec7aa14e-db13-4b05-ac2a-19973ff83e5a",
+                "@id": "enzml:BaseUnit/1be2e5cf-2afd-4b04-a4c7-22cc42fde9b6",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
                 "kind": "second",
-                "exponent": -1,
+                "exponent": 1,
                 "scale": 1.0
               }
             ]
@@ -599,7 +424,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:MeasurementData/0970bcda-cb12-4049-a1e1-9b8c2a59c425",
+          "@id": "enzml:MeasurementData/bbe483a3-d68a-44ed-8acd-0fe94b4b2f7a",
           "@type": [
             "enzml:MeasurementData"
           ],
@@ -615,7 +440,7 @@
             "@type": [
               "OBO:UO_0000000"
             ],
-            "id": "u2",
+            "id": "u1",
             "name": "mmol / l",
             "base_units": [
               {
@@ -624,7 +449,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/801b612f-9b16-4030-bc53-20e00d9e525b",
+                "@id": "enzml:BaseUnit/040c4b08-0af8-41d5-b3b6-0fa479ece06f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -638,7 +463,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/8c63ea70-d26e-45e4-beef-651da82864d0",
+                "@id": "enzml:BaseUnit/5069824d-7d9b-4afd-860d-232049d5fe2f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -658,7 +483,7 @@
             "@type": [
               "OBO:UO_0000000"
             ],
-            "id": "u4",
+            "id": "u2",
             "name": "s",
             "base_units": [
               {
@@ -667,12 +492,12 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/ec7aa14e-db13-4b05-ac2a-19973ff83e5a",
+                "@id": "enzml:BaseUnit/1be2e5cf-2afd-4b04-a4c7-22cc42fde9b6",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
                 "kind": "second",
-                "exponent": -1,
+                "exponent": 1,
                 "scale": 1.0
               }
             ]
@@ -719,7 +544,7 @@
         "@type": [
           "OBO:UO_0000000"
         ],
-        "id": "u5",
+        "id": "u3",
         "name": "K",
         "base_units": [
           {
@@ -728,7 +553,7 @@
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "enzml:BaseUnit/ff8443f5-375d-4fbe-b199-598194298fb4",
+            "@id": "enzml:BaseUnit/a3eac754-8efc-479a-b12d-7910d4881e7f",
             "@type": [
               "enzml:BaseUnit"
             ],
@@ -752,7 +577,7 @@
           "@type": "@id"
         }
       },
-      "@id": "enzml:Measurement/a1fda09a-634e-4482-8d66-069b0e615ef5",
+      "@id": "enzml:Measurement/aed20526-1899-43b8-bf3c-5dea15ff814d",
       "@type": [
         "enzml:Measurement"
       ],
@@ -768,7 +593,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:MeasurementData/8c1fce82-7dbe-499e-b20d-6b0bb4887ed8",
+          "@id": "enzml:MeasurementData/f7fc7642-f8ee-4e28-bfb6-c8ae924a51b0",
           "@type": [
             "enzml:MeasurementData"
           ],
@@ -784,7 +609,7 @@
             "@type": [
               "OBO:UO_0000000"
             ],
-            "id": "u2",
+            "id": "u1",
             "name": "mmol / l",
             "base_units": [
               {
@@ -793,7 +618,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/801b612f-9b16-4030-bc53-20e00d9e525b",
+                "@id": "enzml:BaseUnit/040c4b08-0af8-41d5-b3b6-0fa479ece06f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -807,7 +632,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/8c63ea70-d26e-45e4-beef-651da82864d0",
+                "@id": "enzml:BaseUnit/5069824d-7d9b-4afd-860d-232049d5fe2f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -827,7 +652,7 @@
             "@type": [
               "OBO:UO_0000000"
             ],
-            "id": "u4",
+            "id": "u2",
             "name": "s",
             "base_units": [
               {
@@ -836,12 +661,12 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/ec7aa14e-db13-4b05-ac2a-19973ff83e5a",
+                "@id": "enzml:BaseUnit/1be2e5cf-2afd-4b04-a4c7-22cc42fde9b6",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
                 "kind": "second",
-                "exponent": -1,
+                "exponent": 1,
                 "scale": 1.0
               }
             ]
@@ -884,7 +709,7 @@
               "@type": "@id"
             }
           },
-          "@id": "enzml:MeasurementData/ab6e6d77-58fe-4da1-a310-9224f573f0da",
+          "@id": "enzml:MeasurementData/597c85d3-288f-470f-b7aa-8c156c1f2b27",
           "@type": [
             "enzml:MeasurementData"
           ],
@@ -900,7 +725,7 @@
             "@type": [
               "OBO:UO_0000000"
             ],
-            "id": "u2",
+            "id": "u1",
             "name": "mmol / l",
             "base_units": [
               {
@@ -909,7 +734,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/801b612f-9b16-4030-bc53-20e00d9e525b",
+                "@id": "enzml:BaseUnit/040c4b08-0af8-41d5-b3b6-0fa479ece06f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -923,7 +748,7 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/8c63ea70-d26e-45e4-beef-651da82864d0",
+                "@id": "enzml:BaseUnit/5069824d-7d9b-4afd-860d-232049d5fe2f",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
@@ -943,7 +768,7 @@
             "@type": [
               "OBO:UO_0000000"
             ],
-            "id": "u4",
+            "id": "u2",
             "name": "s",
             "base_units": [
               {
@@ -952,12 +777,12 @@
                   "OBO": "http://purl.obolibrary.org/obo/",
                   "schema": "https://schema.org/"
                 },
-                "@id": "enzml:BaseUnit/ec7aa14e-db13-4b05-ac2a-19973ff83e5a",
+                "@id": "enzml:BaseUnit/1be2e5cf-2afd-4b04-a4c7-22cc42fde9b6",
                 "@type": [
                   "enzml:BaseUnit"
                 ],
                 "kind": "second",
-                "exponent": -1,
+                "exponent": 1,
                 "scale": 1.0
               }
             ]
@@ -1004,7 +829,7 @@
         "@type": [
           "OBO:UO_0000000"
         ],
-        "id": "u5",
+        "id": "u3",
         "name": "K",
         "base_units": [
           {
@@ -1013,7 +838,7 @@
               "OBO": "http://purl.obolibrary.org/obo/",
               "schema": "https://schema.org/"
             },
-            "@id": "enzml:BaseUnit/ff8443f5-375d-4fbe-b199-598194298fb4",
+            "@id": "enzml:BaseUnit/a3eac754-8efc-479a-b12d-7910d4881e7f",
             "@type": [
               "enzml:BaseUnit"
             ],
@@ -1025,5 +850,123 @@
       }
     }
   ],
-  "equations": []
+  "equations": [],
+  "parameters": [
+    {
+      "@context": {
+        "enzml": "http://www.enzymeml.org/v2/",
+        "OBO": "http://purl.obolibrary.org/obo/",
+        "schema": "https://schema.org/",
+        "id": {
+          "@id": "schema:identifier",
+          "@type": "@id"
+        }
+      },
+      "@id": "enzml:Parameter/46faced8-6229-4b7c-b06a-3feb06a11350",
+      "@type": [
+        "enzml:Parameter"
+      ],
+      "id": "kcat",
+      "name": "kcat",
+      "symbol": "kcat",
+      "unit": {
+        "@context": {
+          "enzml": "http://www.enzymeml.org/v2/",
+          "OBO": "http://purl.obolibrary.org/obo/",
+          "schema": "https://schema.org/"
+        },
+        "@id": "OBO:UO_0000010",
+        "@type": [
+          "OBO:UO_0000000"
+        ],
+        "id": "u4",
+        "name": "1 / s",
+        "base_units": [
+          {
+            "@context": {
+              "enzml": "http://www.enzymeml.org/v2/",
+              "OBO": "http://purl.obolibrary.org/obo/",
+              "schema": "https://schema.org/"
+            },
+            "@id": "enzml:BaseUnit/1be2e5cf-2afd-4b04-a4c7-22cc42fde9b6",
+            "@type": [
+              "enzml:BaseUnit"
+            ],
+            "kind": "second",
+            "exponent": -1,
+            "scale": 1.0
+          }
+        ]
+      },
+      "upper": 100.0,
+      "lower": 0.0,
+      "stderr": 0.1,
+      "constant": true
+    },
+    {
+      "@context": {
+        "enzml": "http://www.enzymeml.org/v2/",
+        "OBO": "http://purl.obolibrary.org/obo/",
+        "schema": "https://schema.org/",
+        "id": {
+          "@id": "schema:identifier",
+          "@type": "@id"
+        }
+      },
+      "@id": "enzml:Parameter/706ce185-8f1d-429e-8c0d-76942326a0df",
+      "@type": [
+        "enzml:Parameter"
+      ],
+      "id": "K_m",
+      "name": "K_m",
+      "symbol": "K_m",
+      "unit": {
+        "@context": {
+          "enzml": "http://www.enzymeml.org/v2/",
+          "OBO": "http://purl.obolibrary.org/obo/",
+          "schema": "https://schema.org/"
+        },
+        "@id": "OBO:UO_0000063",
+        "@type": [
+          "OBO:UO_0000000"
+        ],
+        "id": "u1",
+        "name": "mmol / l",
+        "base_units": [
+          {
+            "@context": {
+              "enzml": "http://www.enzymeml.org/v2/",
+              "OBO": "http://purl.obolibrary.org/obo/",
+              "schema": "https://schema.org/"
+            },
+            "@id": "enzml:BaseUnit/040c4b08-0af8-41d5-b3b6-0fa479ece06f",
+            "@type": [
+              "enzml:BaseUnit"
+            ],
+            "kind": "mole",
+            "exponent": 1,
+            "scale": -3.0
+          },
+          {
+            "@context": {
+              "enzml": "http://www.enzymeml.org/v2/",
+              "OBO": "http://purl.obolibrary.org/obo/",
+              "schema": "https://schema.org/"
+            },
+            "@id": "enzml:BaseUnit/5069824d-7d9b-4afd-860d-232049d5fe2f",
+            "@type": [
+              "enzml:BaseUnit"
+            ],
+            "kind": "litre",
+            "exponent": -1,
+            "scale": 1.0
+          }
+        ]
+      },
+      "upper": 100.0,
+      "lower": 0.0,
+      "stderr": 0.1,
+      "constant": true
+    }
+  ]
 }
\ No newline at end of file
diff --git a/tests/fixtures/sbml/reaction_example_sbml.xml b/tests/fixtures/sbml/reaction_example_sbml.xml
index d346fc53..95a3e463 100644
--- a/tests/fixtures/sbml/reaction_example_sbml.xml
+++ b/tests/fixtures/sbml/reaction_example_sbml.xml
@@ -2,22 +2,22 @@
 <sbml xmlns="http://www.sbml.org/sbml/level3/version2/core" level="3" version="2">
     <model name="Test">
         <annotation>
-            <enzymeml:data xmlns:enzymeml="https://www.enzymeml.org/v2" file="data.csv">
-                <enzymeml:measurement id="m0" name="m0" timeUnit="u4">
+            <enzymeml:data xmlns:enzymeml="https://www.enzymeml.org/v2" file="data.tsv">
+                <enzymeml:measurement id="m0" name="m0" timeUnit="u2">
                     <enzymeml:conditions>
                         <enzymeml:ph value="7.0"/>
-                        <enzymeml:temperature value="298.15" unit="u5"/>
+                        <enzymeml:temperature value="298.15" unit="u3"/>
                     </enzymeml:conditions>
-                    <enzymeml:initConc species="s0" unit="u2"/>
-                    <enzymeml:initConc species="s1" value="10.0" unit="u2"/>
+                    <enzymeml:speciesData species="s0" unit="u1" type="CONCENTRATION"/>
+                    <enzymeml:speciesData species="s1" value="10.0" unit="u1" type="CONCENTRATION"/>
                 </enzymeml:measurement>
-                <enzymeml:measurement id="m1" name="m1" timeUnit="u4">
+                <enzymeml:measurement id="m1" name="m1" timeUnit="u2">
                     <enzymeml:conditions>
                         <enzymeml:ph value="7.0"/>
-                        <enzymeml:temperature value="298.15" unit="u5"/>
+                        <enzymeml:temperature value="298.15" unit="u3"/>
                     </enzymeml:conditions>
-                    <enzymeml:initConc species="s0" unit="u2"/>
-                    <enzymeml:initConc species="s1" value="10.0" unit="u2"/>
+                    <enzymeml:speciesData species="s0" unit="u1" type="CONCENTRATION"/>
+                    <enzymeml:speciesData species="s1" value="10.0" unit="u1" type="CONCENTRATION"/>
                 </enzymeml:measurement>
             </enzymeml:data>
         </annotation>
@@ -34,7 +34,7 @@
                     <unit kind="litre" exponent="1" scale="-3"/>
                 </listOfUnits>
             </unitDefinition>
-            <unitDefinition id="u1" name="mmol / l s">
+            <unitDefinition id="u1" name="mmol / l">
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
                         <rdf:Description rdf:about="http://purl.obolibrary.org/obo/UO_0000063">
@@ -45,35 +45,33 @@
                 <listOfUnits>
                     <unit kind="mole" exponent="1" scale="-3"/>
                     <unit kind="litre" exponent="-1" scale="1"/>
-                    <unit kind="second" exponent="-1" scale="1"/>
                 </listOfUnits>
             </unitDefinition>
-            <unitDefinition id="u2" name="mmol / l">
+            <unitDefinition id="u2" name="s">
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
-                        <rdf:Description rdf:about="http://purl.obolibrary.org/obo/UO_0000063">
+                        <rdf:Description rdf:about="http://purl.obolibrary.org/obo/UO_0000010">
                             <rdf:type rdf:resource="http://purl.obolibrary.org/obo/UO_0000000"/>
                         </rdf:Description>
                     </rdf:RDF>
                 </annotation>
                 <listOfUnits>
-                    <unit kind="mole" exponent="1" scale="-3"/>
-                    <unit kind="litre" exponent="-1" scale="1"/>
+                    <unit kind="second" exponent="1" scale="1"/>
                 </listOfUnits>
             </unitDefinition>
-            <unitDefinition id="u3" name="1 / s">
+            <unitDefinition id="u3" name="K">
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
-                        <rdf:Description rdf:about="http://purl.obolibrary.org/obo/UO_0000010">
+                        <rdf:Description rdf:about="http://purl.obolibrary.org/obo/UO_0000012">
                             <rdf:type rdf:resource="http://purl.obolibrary.org/obo/UO_0000000"/>
                         </rdf:Description>
                     </rdf:RDF>
                 </annotation>
                 <listOfUnits>
-                    <unit kind="second" exponent="-1" scale="1"/>
+                    <unit kind="kelvin" exponent="1" scale="1"/>
                 </listOfUnits>
             </unitDefinition>
-            <unitDefinition id="u4" name="s">
+            <unitDefinition id="u4" name="1 / s">
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
                         <rdf:Description rdf:about="http://purl.obolibrary.org/obo/UO_0000010">
@@ -85,18 +83,6 @@
                     <unit kind="second" exponent="-1" scale="1"/>
                 </listOfUnits>
             </unitDefinition>
-            <unitDefinition id="u5" name="K">
-                <annotation>
-                    <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
-                        <rdf:Description rdf:about="http://purl.obolibrary.org/obo/UO_0000012">
-                            <rdf:type rdf:resource="http://purl.obolibrary.org/obo/UO_0000000"/>
-                        </rdf:Description>
-                    </rdf:RDF>
-                </annotation>
-                <listOfUnits>
-                    <unit kind="kelvin" exponent="1" scale="1"/>
-                </listOfUnits>
-            </unitDefinition>
         </listOfUnitDefinitions>
         <listOfCompartments>
             <compartment id="v0" name="Vessel 1" size="10" units="u0" constant="true">
@@ -104,7 +90,7 @@
                     <rdf:RDF xmlns:OBO="http://purl.obolibrary.org/obo/"
                              xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:schema="https://schema.org/">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Vessel/774cead8-8a1c-45e4-820a-59a8fc15fb6b">
+                                rdf:about="http://www.enzymeml.org/v2/Vessel/a2ea41db-032c-4a61-a7d5-254137d0bce9">
                             <schema:name>Vessel 1</schema:name>
                             <OBO:OBI_0002139 rdf:datatype="http://www.w3.org/2001/XMLSchema#double">10.0
                             </OBO:OBI_0002139>
@@ -121,7 +107,7 @@
                     <rdf:RDF xmlns:OBO="http://purl.obolibrary.org/obo/"
                              xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:schema="https://schema.org/">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Protein/d69d42cc-c6ac-499c-9a6e-1050b0fc852f">
+                                rdf:about="http://www.enzymeml.org/v2/Protein/42828d0d-f4ac-489b-acd5-cd74c080f340">
                             <schema:name>Enzyme</schema:name>
                             <OBO:GSSO_007262>MTEY</OBO:GSSO_007262>
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/Protein"/>
@@ -138,7 +124,7 @@
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:schema="https://schema.org/">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/SmallMolecule/c8c7ade0-c508-40b8-992c-cc31b879857b">
+                                rdf:about="http://www.enzymeml.org/v2/SmallMolecule/e794f30d-51ea-4b89-a5d7-555bcd70efe5">
                             <schema:name>Substrate</schema:name>
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/SmallMolecule"/>
                         </rdf:Description>
@@ -150,7 +136,7 @@
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:schema="https://schema.org/">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/SmallMolecule/949324fb-6d78-4c38-90d3-79ed2c519ef8">
+                                rdf:about="http://www.enzymeml.org/v2/SmallMolecule/4b8a1f78-1874-447a-aee7-a80970bb1301">
                             <schema:name>Product</schema:name>
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/SmallMolecule"/>
                         </rdf:Description>
@@ -159,11 +145,11 @@
             </species>
         </listOfSpecies>
         <listOfParameters>
-            <parameter id="K_m" name="K_m" units="u2" constant="true">
+            <parameter id="kcat" name="kcat" units="u4" constant="true">
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Parameter/6c2c19f3-31bd-49bc-abd6-af885a7666f9">
+                                rdf:about="http://www.enzymeml.org/v2/Parameter/46faced8-6229-4b7c-b06a-3feb06a11350">
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/Parameter"/>
                         </rdf:Description>
                     </rdf:RDF>
@@ -174,11 +160,11 @@
                     </enzymeml:parameter>
                 </annotation>
             </parameter>
-            <parameter id="kcat" name="kcat" units="u3" constant="true">
+            <parameter id="K_m" name="K_m" units="u1" constant="true">
                 <annotation>
                     <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
                         <rdf:Description
-                                rdf:about="http://www.enzymeml.org/v2/Parameter/df6b446a-f1d6-4c79-af46-7af042b1d2a7">
+                                rdf:about="http://www.enzymeml.org/v2/Parameter/706ce185-8f1d-429e-8c0d-76942326a0df">
                             <rdf:type rdf:resource="http://www.enzymeml.org/v2/Parameter"/>
                         </rdf:Description>
                     </rdf:RDF>
@@ -204,8 +190,8 @@
                 <kineticLaw>
                     <annotation>
                         <enzymeml:variables xmlns:enzymeml="https://www.enzymeml.org/v2">
-                            <enzymeml:variable id="s0" name="s0" symbol="s0"/>
                             <enzymeml:variable id="p0" name="p0" symbol="p0"/>
+                            <enzymeml:variable id="s0" name="s0" symbol="s0"/>
                         </enzymeml:variables>
                     </annotation>
                     <math xmlns="http://www.w3.org/1998/Math/MathML">
diff --git a/tests/fixtures/sbml/reactions_example.omex b/tests/fixtures/sbml/reactions_example.omex
new file mode 100644
index 00000000..ce6e4e12
Binary files /dev/null and b/tests/fixtures/sbml/reactions_example.omex differ
diff --git a/tests/integration/test_sbml.py b/tests/integration/test_sbml.py
new file mode 100644
index 00000000..f6acb232
--- /dev/null
+++ b/tests/integration/test_sbml.py
@@ -0,0 +1,40 @@
+from pathlib import Path
+
+from pyenzyme import EnzymeMLDocument
+from pyenzyme.tools import to_dict_wo_json_ld
+
+
+class TestSBML:
+    def test_parse_sbml_odes(self):
+        # Arrange
+        path = Path("tests/fixtures/sbml/odes_example.omex")
+
+        # Act
+        enzmldoc = EnzymeMLDocument.from_sbml(path)
+
+        # Assert
+        parsed_doc = to_dict_wo_json_ld(enzmldoc)
+        expected_doc = to_dict_wo_json_ld(
+            EnzymeMLDocument.read("tests/fixtures/sbml/ode_example_enzml.json")
+        )
+
+        assert (
+            parsed_doc == expected_doc
+        ), "Parsed document does not match expected document"
+
+    def test_parse_sbml_reactions(self):
+        # Arrange
+        path = Path("tests/fixtures/sbml/reactions_example.omex")
+
+        # Act
+        enzmldoc = EnzymeMLDocument.from_sbml(path)
+
+        # Assert
+        parsed_doc = to_dict_wo_json_ld(enzmldoc)
+        expected_doc = to_dict_wo_json_ld(
+            EnzymeMLDocument.read("tests/fixtures/sbml/reaction_example_enzml.json")
+        )
+
+        assert (
+            parsed_doc == expected_doc
+        ), "Parsed document does not match expected document"
diff --git a/tests/unit/test_equations.py b/tests/unit/test_equations.py
index 4a1496cc..f0b20cec 100644
--- a/tests/unit/test_equations.py
+++ b/tests/unit/test_equations.py
@@ -2,16 +2,22 @@
 
 from pyenzyme.equations._chem import build_reaction, build_reactions
 from pyenzyme.equations._math import build_equation, build_equations
-from pyenzyme.model import EquationType
+from pyenzyme.model import EquationType, EnzymeMLDocument
+from pyenzyme.units import s
 
 
 class TestMathEquations:
     def test_parse_equation(self):
         # Arrange
+        enzmldoc = EnzymeMLDocument(name="Test")
         equation = "s1'(t) = kcat * p0(t) * s0(t)"
 
         # Act
-        equation = build_equation(equation)
+        equation = build_equation(
+            equation=equation,
+            unit_mapping={"kcat": 1 / s},
+            enzmldoc=enzmldoc,
+        )
 
         # Assert
         expected_vars = ["p0", "s0"]
@@ -23,41 +29,54 @@ def test_parse_equation(self):
         assert (
             equation.equation == "kcat*p0*s0"
         ), "Equation is not correct. Got {equation.equation.equation}"
-        assert equation.parameters[0].name == "kcat", "Parameter name is not correct"
-        assert (
-            equation.parameters[0].symbol == "kcat"
-        ), "Parameter symbol is not correct"
 
         for var in equation.variables:
             assert var.name in expected_vars
             assert var.symbol in expected_vars
 
-        for param in equation.parameters:
+        for param in enzmldoc.parameters:
             assert param.name in expected_params
             assert param.symbol in expected_params
+            assert param.id in expected_params
+            assert param.unit is not None
 
     def test_invalid_equation_no_right(self):
         # Arrange
+        enzmldoc = EnzymeMLDocument(name="Test")
         equation = "s1'(t) ="
 
         # Act
         with pytest.raises(ValueError):
-            equation = build_equation(equation)
+            build_equation(
+                equation=equation,
+                unit_mapping={"kcat": 1 / s},
+                enzmldoc=enzmldoc,
+            )
 
     def test_invalid_equation_no_equals(self):
         # Arrange
+        enzmldoc = EnzymeMLDocument(name="Test")
         equation = "s1'(t) kcat * p0(t) * s0(t)"
 
         # Act
         with pytest.raises(ValueError):
-            equation = build_equation(equation)
+            build_equation(
+                equation=equation,
+                unit_mapping={"kcat": 1 / s},
+                enzmldoc=enzmldoc,
+            )
 
     def test_equation_with_funs(self):
         # Arrange
+        enzmldoc = EnzymeMLDocument(name="Test")
         equation = "s1'(t) = kcat * exp(p0(t) * t)"
 
         # Act
-        equation = build_equation(equation)
+        equation = build_equation(
+            equation=equation,
+            unit_mapping={"kcat": 1 / s},
+            enzmldoc=enzmldoc,
+        )
 
         # Assert
         assert (
@@ -69,10 +88,15 @@ def test_equation_with_funs(self):
 
     def test_equation_with_fun_only_t(self):
         # Arrange
+        enzmldoc = EnzymeMLDocument(name="Test")
         equation = "s1'(t) = kcat * exp(t)"
 
         # Act
-        equation = build_equation(equation)
+        equation = build_equation(
+            equation=equation,
+            unit_mapping={"kcat": 1 / s},
+            enzmldoc=enzmldoc,
+        )
 
         # Assert
         assert (
@@ -84,23 +108,32 @@ def test_equation_with_fun_only_t(self):
 
     def test_multiple_equations(self):
         # Arrange
+        enzmldoc = EnzymeMLDocument(name="Test")
         equations = [
             "s1'(t) = kcat * E_tot * s0(t)",
             "E_tot = p0(t) + p1(t)",
         ]
 
         # Act
-        equations = build_equations(*equations)
+        equations = build_equations(
+            *equations,
+            unit_mapping={"kcat": 1 / s},
+            enzmldoc=enzmldoc,
+        )
 
         # Assert
         assert len(equations) == 2, f"Expected 2 equations. Got {len(equations)}"
 
     def test_init_assigment_equation(self):
         # Arrange
+        enzmldoc = EnzymeMLDocument(name="Test")
         equation = "E_tot = p0 + p1"
 
         # Act
-        equation = build_equation(equation)
+        equation = build_equation(
+            equation,
+            enzmldoc=enzmldoc,
+        )
 
         # Assert
         assert (
@@ -115,10 +148,14 @@ def test_init_assigment_equation(self):
 
     def test_assigment_equation(self):
         # Arrange
+        enzmldoc = EnzymeMLDocument(name="Test")
         equation = "E_tot(t) = p0 + p1"
 
         # Act
-        equation = build_equation(equation)
+        equation = build_equation(
+            equation=equation,
+            enzmldoc=enzmldoc,
+        )
 
         # Assert
         assert (