Class TIfcPropertyDependencyRelationship

Description

Hierarchy

Methods

Properties

Unit

CastleIfc

Declaration

type TIfcPropertyDependencyRelationship = class(TIfcResourceLevelRelationship)

Description

Whilst the IfcPropertyDependencyRelationship may be used to describe the dependency, and it may do so in terms of the expression of how the dependency operates, it is not possible through the current IFC model for the value of the related property to be actually derived from the value of the relating property. The determination of value according to the dependency is required to be performed by an application that can then use the Expression attribute to flag the form of the dependency.

Spec: https://standards.buildingsmart.org/IFC/RELEASE/IFC4_3/HTML/lexical/IfcPropertyDependencyRelationship.htm

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 1121).

Hierarchy

TObject
TPersistent
TComponent
TIfcPersistent
TIfcResourceLevelRelationship
TIfcPropertyDependencyRelationship

Show Additional Members: Inherited Protected

Overview

Methods

Protected	`function WantsGlobalId: Boolean; virtual;`
Protected	`class function IfcClassName: String; virtual;`

Properties

Published	`property GlobalId: String read FGlobalId write FGlobalId;`
Published	`property Name: TIfcLabel read FName write FName;`
Published	`property Description: TIfcText read FDescription write FDescription;`
Published	`property DependingProperty: TIfcProperty read FDependingProperty write FDependingProperty;`
Published	`property DependantProperty: TIfcProperty read FDependantProperty write FDependantProperty;`
Published	`property Expression: TIfcText read FExpression write FExpression;`

Description

Methods

Protected function WantsGlobalId: Boolean; virtual;

This item is declared in ancestor TIfcPersistent.

If True, instances of this class will have GlobalId auto-assigned at saving, and they will be saved as part of the "data" list in IFC JSON files.

Strictly following the spec, this should be only defined for TIfcRoot, because only IfcRoot has GlobalId. In reality, we need GlobalId at TIfcPersistent to load some files, and we sometimes need WantsGlobalId = True to save some files.

Source: scene/load/ifc/castleifc_ifc_types.inc (line 52).

Protected class function IfcClassName: String; virtual;

This item is declared in ancestor TIfcPersistent.

Name for the IFC standard, used in IFC files. By default, this is just ClassName with prefix 'T' removed.

Source: scene/load/ifc/castleifc_ifc_types.inc (line 56).

Properties

Published property GlobalId: String read FGlobalId write FGlobalId;

This item is declared in ancestor TIfcPersistent.

Globally unique identifier for the object instance.

Note: Not declared as TGUID, because TGUID cannot be published, but also we don't really need it: for our purposes, this identifier is just an arbitrary string.

Note: IFC 4.3 specification puts this only at IfcRoot, not at every IFC class. But testcase https://github.com/buildingsmart-community/Community-Sample-Test-Files/blob/main/IFC%204.0.2.1%20(IFC%204)/ISO%20Spec%20archive/wall-with-opening-and-window.json (from IFC 4.0) shows this can be present at any IFC class, in particular TIfcGeometricRepresentationContext.

In fact, TIfcGeometricRepresentationContext needs to have GlobalId to be successfully saved (avoid recursively trying to serialize it) in some cases. We indicate such classes with WantsGlobalId.

IFC JSON documentation says this, which seems to (unfortunately it is not unambiguous enough...) allow this at any IFC class: "Whereas the globalId attribute is only available to those elements that are descendent of the IfcRoot entity in the EXPRESS schema, we encourage a broader use of this globalId, to enable referencing between objects in a JSON file when useful.".

Source: scene/load/ifc/castleifc_ifc_types.inc (line 79).

Published property Name: TIfcLabel read FName write FName;

This item is declared in ancestor TIfcResourceLevelRelationship.

A name used to identify or qualify the relationship.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 1105).

Published property Description: TIfcText read FDescription write FDescription;

This item is declared in ancestor TIfcResourceLevelRelationship.

A description that may apply additional information about the relationship.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 1108).

Published property DependingProperty: TIfcProperty read FDependingProperty write FDependingProperty;

The property on which the relationship depends.

Source: scene/load/ifc/castleifc_ifc_standard_types.inc (line 1128).