diff --git a/src/main/java/de/samply/directory_sync_service/directory/DirectoryApi.java b/src/main/java/de/samply/directory_sync_service/directory/DirectoryApi.java
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+++ b/src/main/java/de/samply/directory_sync_service/directory/DirectoryApi.java
@@ -0,0 +1,102 @@
+package de.samply.directory_sync_service.directory;
+
+import de.samply.directory_sync_service.directory.model.Biobank;
+import de.samply.directory_sync_service.directory.model.DirectoryCollectionGet;
+import de.samply.directory_sync_service.directory.model.DirectoryCollectionPut;
+import de.samply.directory_sync_service.model.BbmriEricId;
+import de.samply.directory_sync_service.model.StarModelData;
+import org.hl7.fhir.r4.model.OperationOutcome;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * The DirectoryApi class provides an interface for interacting with the Directory service.
+ * This class allows for fetching and updating biobank and collection information, managing star models,
+ * and performing various validation and correction operations.
+ * It supports a mock mode for testing purposes, where no real Directory interactions are performed.
+ */
+public abstract class DirectoryApi {
+  protected static final Logger logger = LoggerFactory.getLogger(DirectoryApi.class);
+  // Setting this variable to true will prevent any contact being made to the Directory.
+  // All public methods will return feasible fake results.
+  protected boolean mockDirectory = false;
+
+  /**
+   * Constructs a new DirectoryApiRest instance.
+   * If we are not in mocking mode, log in to the Directory.
+   *
+   * @param baseUrl The base URL of the Directory service.
+   * @param mockDirectory If true, the instance operates in mock mode, returning fake data.
+   * @param username The username for authenticating with the Directory.
+   * @param password The password for authenticating with the Directory.
+   */
+  public DirectoryApi(String baseUrl, boolean mockDirectory, String username, String password) {
+    this.mockDirectory = mockDirectory;
+  }
+
+  /**
+     * @return true if this API is accessible, false otherwise.
+   */
+  public abstract boolean isAvailable();
+
+  /**
+   * Log in to the Directory. You can log in as many times as you like.
+   */
+  public abstract boolean login();
+
+  /**
+   * Fetches the Biobank with the given {@code id}.
+   *
+   * @param id the ID of the Biobank to fetch.
+   * @return either the Biobank or null if an error occurs
+   */
+  public abstract Biobank fetchBiobank(BbmriEricId id);
+
+  /**
+   * Make API calls to the Directory to fill a DirectoryCollectionGet object containing attributes
+   * for all of the collections listed in collectionIds. The countryCode is used solely for
+   * constructing the URL for the API call.
+   * 
+   * @param countryCode E.g. "DE".
+   * @param collectionIds IDs of the collections whose data will be harvested.
+   * @return
+   */
+  public abstract DirectoryCollectionGet fetchCollectionGetOutcomes(String countryCode, List<String> collectionIds);
+
+  /**
+   * Send aggregated collection information to the Directory.
+   *
+   * @param directoryCollectionPut Summary information about one or more collections
+   * @return an outcome, either successful or null
+   */
+  public abstract boolean updateEntities(DirectoryCollectionPut directoryCollectionPut);
+
+  /**
+   * Updates the Star Model data in the Directory service based on the provided StarModelInputData.
+   * <p>
+   * Before sending any star model data to the Directory, the original
+   * star model data for all known collections will be deleted from the
+   * Directory.
+   *
+   * @param starModelInputData The input data for updating the Star Model.
+   * @return An OperationOutcome indicating the success or failure of the update.
+   */
+  public abstract OperationOutcome updateStarModel(StarModelData starModelInputData);
+
+  /**
+   * Collects diagnosis corrections from the Directory.
+   * <p>
+   * It checks with the Directory if the diagnosis codes are valid ICD values and corrects them if necessary.
+   * <p>
+   * Two levels of correction are possible:
+   * <p>
+   * 1. If the full code is not correct, remove the number after the period and try again. If the new truncated code is OK, use it to replace the existing diagnosis.
+   * 2. If that doesn't work, replace the existing diagnosis with null.
+   *
+   * @param diagnoses A string map containing diagnoses to be corrected.
+   */
+  public abstract void collectDiagnosisCorrections(Map<String, String> diagnoses);
+}