IfcExternalReference

Definition from IAI: An IfcExternalReference is the identification of information that is not explicitly represented in the current model or in the project database (as an implementation of the current model). Such information may be contained in classifications, documents or libraries.

Only the Location (e.g. as an URL) is given to describe the place where the information can be found. Also an optional ItemReference as a key to allow more specific references (as to sections or tables) is provided. The ItemReference defines a system interpretable method to identify the relevant part of information at the data source (given by Location). In addition a human interpretable Name can be assigned to identify the information subject (e.g. classification code).

IfcExternalReference is an abstract supertype of all external reference classes.

> HISTORY: New Class in IFC Release 2x to generalize means of referencing available in IFC Release 2.0.

### Use Definitions

See the use definitions given at the subtypes of IfcExternalReference.

EXPRESS specification:

ENTITY IfcExternalReference
ABSTRACT SUPERTYPE OF | (ONEOF(IfcLibraryReference, IfcClassificationReference, IfcDocumentReference));
Location | : | OPTIONAL IfcLabel;
ItemReference | : | OPTIONAL IfcIdentifier;
Name | : | OPTIONAL IfcLabel;
WHERE
WR1 | : | EXISTS(ItemReference) OR EXISTS(Location) OR EXISTS(Name);
END_ENTITY;

Attribute definitions:

Location | : | Location, where the external source (classification, document or library). This can be either human readable or computer interpretable. For electronic location normally given as an URL location string, however other ways of accessing external references may be established in an application scenario.
ItemReference | : | Identifier for the referenced item in the external source (classification, document or library). The internal reference can provide a computer interpretable pointer into electronic source.
Name | : | Optional name to further specify the reference. It can provide a human readable identifier (which does not necessarily need to have a counterpart in the internal structure of the document).

Formal Propositions:

WR1 | : | One of the attributes of IfcExternalReference should have a value assigned.

Inheritance graph

ENTITY IfcExternalReference;
ENTITY IfcExternalReference;
Location | : | OPTIONAL IfcLabel;
ItemReference | : | OPTIONAL IfcIdentifier;
Name | : | OPTIONAL IfcLabel;
END_ENTITY;