Proposal to change the logic of the partof-facet. (#171)

Development/ids.xsd

@@ -51,9 +51,9 @@
 	</xs:complexType>
 	<xs:complexType name="partOfType">
 		<xs:sequence>
-			<xs:element name="entity" type="ids:entityType" minOccurs="0"/>
+			<xs:element name="entity" type="ids:entityType" minOccurs="1" />
 		</xs:sequence>
-		<xs:attribute name="relation" type="ids:relations" use="required"/>
+		<xs:attribute name="relation" type="ids:relations" />
 	</xs:complexType>
 	<xs:complexType name="applicabilityType">
 		<xs:sequence>

Documentation/partof-facet.md

@@ -2,26 +2,32 @@
 
 Objects in IFC can have relationships to other objects. IDS supports specifying four types of relationships.
 
-The **IfcRelAggregates** relationship describes how multiple smaller subobjects can be aggregated into a single bigger object. For example, many building storeys make up a building. Alternatively, many beams, floor boards, and joints make up a slab. Or perhaps many brackets, mullions, and steel plates make up an assembly.
+The **IfcRelAggregates** relationship describes how multiple smaller sub-objects can be aggregated into a single bigger object. For example, many building storeys make up a building. Alternatively, many beams, floor boards, and joints make up a slab. Or perhaps many brackets, mullions, and steel plates make up an assembly.
 
-The **IfcRelAssignsToGroup** relationship describes how multiple objects can be grouped into a collection of objects any usecase. For example, ducts, AHUs, fans, and louvres may all be grouped into a single distribution system.  Alternatively, cables, distribution boards, and GPOs may be grouped into a single circuit. Or perhaps spaces are grouped into zones, or maintainable assets are grouped into an inventory.
+The **IfcRelAssignsToGroup** relationship describes how multiple objects can be grouped into a collection of objects any use-case. For example, ducts, AHUs, fans, and louvres may all be grouped into a single distribution system.  Alternatively, cables, distribution boards, and GPOs may be grouped into a single circuit. Or perhaps spaces are grouped into zones, or maintainable assets are grouped into an inventory.
 
 The **IfcRelContainedInSpatialStructure** relationship describes how multiple objects can be located in a particular location. For example, a pump might be in a space, a column might be on the level 2 building storey, or some street furniture might be on the building site. Every object must have a single primary location container in IFC, even though they may be referenced in multiple locations (such as a multi-storey column). This relationship only targets the primary location container.
 
 The **IfcRelNests** relationship describes how a physical object may be connected to a larger host object, typically through a physical connection such as a pre-drilled hole or connection terminal. When the host moves, the attached nested objects move with it.
 
+The **IfcRelVoidsElement** relationship describes how a void belongs to an element.
+
+The **IfcRelFillsElement** relationship describes how an element fills an a void, potentially making it part .
+
 ## Parameters
 
-Parameter | Required | Restrictions Allowed | Allowed Values | Meaning
---- | --- | --- | --- | ---
-**Relation** | ✔️ | ❌ | One relationship chosen from the 4 supported relationships: IfcRelAggregates, IfcRelAssignsToGroup, IfcRelContainedInSpatialStructure, or IfcRelNests | The smaller subobject has the specified relationship with a larger object
-**Entity** | ❌ | ✔️ | Any valid IFC class name (e.g. "IFCSYSTEM") | The IFC class of the larger object must match exactly.
+| Parameter    | Required | Restrictions Allowed | Allowed Values                                                  | Meaning                                                                    |
+| ------------ | -------- | -------------------- | --------------------------------------------------------------- | -------------------------------------------------------------------------- |
+| **Entity**   | ✔️     | ❌                   | Any valid IFC entity (e.g. "IFCSYSTEM")                         | The IFC class of the larger object must match exactly.                     |
+| **Relation** | ❌       | ✔️                 | One relationship chosen from the 6 supported types listed above | If omitted any valid IFC relationship structure that directly or indirectly, and transitively (recursively) has to be evaluated, if specified only the given type must be evaluated (recursively) |
 
 ## Examples
 
 Applicability Intention | Requirement Intention | Facet Definition
 --- | --- | ---
-Any entity that is part of a curtain wall | The entity (e.g. mullion) must be part of a curtain wall | Relation="IfcRelAggregates", Entity="IFCCURTAINWALL"
+Any entity that is directly composing a curtain wall | The entity (e.g. mullion) must be part of a curtain wall | Relation="IfcRelAggregates", Entity="IFCCURTAINWALL"
+Any entity that is directly or indirectly part of a curtain wall | The entity (e.g. mullion) must be part of a curtain wall | Entity="IFCCURTAINWALL"
 Any entity that is part of a distribution system | The entity (e.g. duct) must be part of a distribution system | Relation="IfcRelAssignsToGroup", Entity="IFCDISTRIBUTIONSYSTEM"
 Any entity that is located in a space | The entity (e.g. pump) must be located in a space | Relation="IfcRelContainedInSpatialStructure", Entity="IFCSPACE"
-Any entity that hosted by a hand wash basin | The entity (e.g. facuet) must be fixed on a hand wash basin | Relation="IfcRelNests", Entity="IFCSANITARYTERMINAL"
+Any entity that hosted by a hand wash basin | The entity (e.g. faucet) must be fixed on a hand wash basin | Relation="IfcRelNests", Entity="IFCSANITARYTERMINAL"
+Any window that hosted by a hand wash basin | The entity (e.g. faucet) must be fixed on a hand wash basin | Relation="IfcRelNests", Entity="IFCSANITARYTERMINAL"