EXPRESS Definition
EXPRESS-G Diagram
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EXPRESS Definition |
EXPRESS-G Diagram |
No Simple Types defined in this Schema
No Select Types defined in this Schema
No Enumerations defined in this Schema
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
No Functions defined in this Schema
This schema defines the representation of shape and topology as important definitional properties for products defined within the IFC Object Model. The representations characterize certain properties of a product, and any product can be defined by zero, one, or many of those properties.
The schema defines two ways to represent definitional properties of products:
- topological representation
- geometric shape representation
The geometric shape representation allows for
- multiple shape representations for the same product definition shape of a product
- separate shape representations for components or parts of the product definition shape by using shape aspects
The following parts of ISO10303, STEP, had been reviewed to provide input into the specification of the representation resource for the IFC Object Model:
- Part 41, Integrated Generic Resources – Fundamental of Product Description and Support
- product_property_definition_schema
- product_property_representation_schema
- Part 42, Integrated Generic Resources – Geometric and Topological Representation
- geometry_schema
- Part 43, Integrated Generic Resources – Representation Structures
- representation_schema
Please note, that the above listed resources which are defined within Integrated Resources of STEP had been interpreted to fit into the IFC architecture.
 Fully Attributed View |
EXPRESS Definition |
Definition from ISO/CD 10303-42:1992: A geometric representation context is a representation context in which the geometric representation items are geometrically founded. A geometric representation context is a distinct coordinate space, spatially unrelated to other coordinate spaces.
Definition from IAI: The IfcGeometricRepresentationContext defines the context that applies to several shape representations of a product. It defines the type of the context in which the shape representation is defined, that can be used to describe the level of detailing for which the shape representation is valid (inherited from the supertype), and the numeric precision applicable to the geometric representation items defined in this context.
NOTE: The definition of this class relates to the STEP entity geometric_representation_context. Please refer to ISO/IS 10303-42:1994 for the final definition of the formal standard.
New Class in IFC Release 2.0
ISSUE: No issues raised so far.
IfcRepresentationContext
IfcGeometricRepresentationContext
Attribute type (OPT, DER, INV)
Redefinition (SELF)
Attribute / Relation
Data or Rel. type
Definition
CoordinateSpaceDimension
The integer dimension count of the coordinate space modeled in a geometric representation context.
OPT
Precision
REAL
Value of the model precision for geometric models. It is a double value (REAL), typically in 1E-5 to 1E-8 range, that indicates the tolerance under which two given points are still assumed to be identical. The value can be used e.g. to sets the maximum distance from an edge curve to the underlying face surface in brep models.
WR21
The rule constrains the supported values of context type for this subtype in this release.
SELF\IfcRepresentationContext.ContextType IN ['Sketch','Outline','Design','Detail','UserDefined','NotDefined']
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Fully Attributed View |
EXPRESS Definition |
Definition from ISO/CD 10303-42:1992: A product definition shape identifies a product’s shape as the conceptual idea of the form of a product.
Definition from IAI: The IfcProductDefinitionShape defines all shape relevant information about an IfcProduct. It allows for multiple geometric shape representations of the same product.
This Class has changed after IFC Release 1.5.1, please see the Migration Guide for details
: The definition of this class relates to the STEP entity product_definition_shape. Please refer to ISO/IS 10303-41:1994 for the final definition of the formal standard.
ISSUE: See issues I-041, I-044, I-047, I-048, GI-002, GI-003 for changes made in IFC Release 1.5.
See issue I-330 for changes made in IFC Release 1.5.1.
IfcProductRepresentation
Attribute type (OPT, DER, INV)
Redefinition (SELF)
Attribute / Relation
Data or Rel. type
Definition
ShapeRepresentations
LIST [1:?] OF IfcShapeRepresentation
Contained list of shape representations. Each member defining a valid shape representation of a particular type (i.e. bounding box, standard, advance, and arbitrary) within a particular representation context.
INV
HasShapeAspects
SET [0:?] OF IfcShapeAspect
Reference to the shape representation, explicitly indication aspects or components of the product shape.
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Fully Attributed View |
EXPRESS Definition |
Definition from IAI: The IfcProductDefinitionTopology defines the topology of a product. The product definition topology is used for products that are defined within a network. The product definition topology then specifies the connectivity of that product. It does not allow for multiple topological representations of the product, only a single topology can be given.
New Class in IFC Release 2.0
ISSUE: See I-522 for changes made in IFC Release 2.0.
IfcProductRepresentation
Attribute type (OPT, DER, INV)
Redefinition (SELF)
Attribute / Relation
Data or Rel. type
Definition
TopologyRepresentation
Contained topology representation representing the topology and connectivity of the product.
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EXPRESS Definition |
Definition from IAI: The IfcProductRepresentation is a property that defines a property defining a product, including its (geometrical or topological) representation. A product can have zero, one or many of such product representations, and a single product representation can be shared among various products.
NOTE: The definition of this class relates to the STEP entity property_definition. The use of the term ‘property’ was avoided since it conflicts with the property, property type, and property set definitions elsewhere in the IFC Object Model.
New Class in IFC Release 2.0
ISSUE: No issues raised so far.
IfcProductRepresentation
IfcProductDefinitionShape
IfcProductDefinitionTopology
Attribute type (OPT, DER, INV)
Redefinition (SELF)
Attribute / Relation
Data or Rel. type
Definition
GlobalId
Assignment of a globally unique identifier that allows to ensure uniqueness in a global context.
OwnerHistory
Assignment of the information about the current ownership of that object, including owning actor, application, local identification and information captured about the recent changes of the object.
OPT
Name
STRING
The word or group of words by which the product definition is known.
OPT
Description
STRING
The word or group of words that characterize the product definition. It can be used to add additional meaning the the name of the product definition.
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EXPRESS Definition |
Definition from ISO/CD 10303-42:1992: A representation is one or more representation items that are related in a specified representation context as the representation of some concept.
Definition from IAI: The IfcRepresentation defines the general concept of representing product properties.
NOTE: The definition of this class relates to the STEP entity representation. Please refer to ISO/IS 10303-43:1994 for the final definition of the formal standard.
New Class in IFC Release 2.0
ISSUE: No issues raised so far.
IfcRepresentation
Attribute type (OPT, DER, INV)
Redefinition (SELF)
Attribute / Relation
Data or Rel. type
Definition
ContextOfItems
Definition of the representation context for which the different subtypes of representation are valid.
RepresentationIdentifier
STRING
The representation identifier that may provide the primary identification of the representation.
RepresentationType
STRING
The description of the type of a representation context. The supported values for context type are specified in a clause for each release.
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EXPRESS Definition |
Definition from ISO/CD 10303-42:1992: A representation context is a context in which a set of representation items are related.
Definition from IAI: The IfcRepresentationContext defines the context to which the representations of product definition shape or product definition topology are related.
NOTE: The definition of this class relates to the STEP entity representation_context. Please refer to ISO/IS 10303-43:1994 for the final definition of the formal standard.
This Class has changed after IFC Release 1.5.1, please see the Migration Guide for details
ISSUE: See issues I-049, I-051 for changes made in IFC Release 1.5.
IfcRepresentationContext
Attribute type (OPT, DER, INV)
Redefinition (SELF)
Attribute / Relation
Data or Rel. type
Definition
GlobalId
Assignment of a globally unique identifier that allows to ensure uniqueness in a global context.
ContextIdentifier
STRING
The identifier of the representation context as used within a project.
ContextType
STRING
The description of the type of a representation context. The supported values for context type are specified in a clause for each release.
INV
RepresentationsInContext
SET [1:?] OF IfcRepresentation
All shape representations that are defined in the same representation context.
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EXPRESS Definition |
Definition from ISO/CD 10303-42:1992: The shape aspect is an identifiable element of the shape of a product.
Definition from IAI: The IfcShapeAspect allows for grouping of shape representation items that represent aspects (or components) of the shape of a product. Thereby shape representations of components of the product shape representing a distinctive part of a product that can be explicitly addressed.
NOTE: The definition of this class relates to the STEP entity shape_aspect. Please refer to ISO/IS 10303-41:1994 for the final definition of the formal standard.
This Class has changed after IFC Release 1.5.1, please see the Migration Guide for details
ISSUE: See issues I-330 for changes made in IFC Release 1.5.1.
This Class does not have any Superclasses or Subclasses
Attribute type (OPT, DER, INV)
Redefinition (SELF)
Attribute / Relation
Data or Rel. type
Definition
GlobalId
Assignment of a globally unique identifier that allows to ensure uniqueness in a global context.
ShapeRepresentations
LIST [1:?] OF IfcShapeRepresentation
Contained list of shape representations. Each member defining a valid shape representation of a particular type (i.e. bounding box, attribute driven, explicit) within a particular representation context.
OPT
Name
STRING
The word or group of words by which the shape_aspect is known. It is a tag to indicate the particular semantic of a component within the product definition shape, used to provide meaning. Example: use the tag "Glazing” to define which component of a window shape defines the glazing area.
OPT
Description
STRING
The word or group of words that characterize the shape_aspect. It can be used to add additional meaning the the name of the aspect.
ProductDefinitional
LOGICAL
An indication that the shape aspect is on the physical boundary of the product_definition_shape. If the value of this attribute is TRUE, it shall be asserted that the shape_aspect being identified is on such a boundary. If the value is FALSE, it shall be asserted that the shape_aspect being identified is not on such a boundary. If the value is UNKNOWN, it shall be asserted that it is not known whether or not the shape_aspect being identified is on such a boundary. EXAMPLE: Would be FALSE for a center line, identified as shape aspect, would be TRUE for a cantilever.
PartOfProductDefinitionShape
Reference to the product definition shape of which this class is an aspect.
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Fully Attributed View |
EXPRESS Definition |
Definition from ISO/CD 10303-42:1992: The shape representation is a specific kind of representation that represents a shape.
Definition from IAI: The IfcShapeRepresentation represents the concept of a particular geometric representation of a product or a product component within a special geometric representation context.
NOTE: The definition of this class relates to the STEP entity shape_representation. Please refer to ISO/IS 10303-41:1994 for the final definition of the formal standard.
This Class has changed after IFC Release 1.5.1, please see the Migration Guide for details
ISSUE: See issues I-043, I-052, I-184, I-194 for changes made in IFC Release 1.5.
IfcRepresentation
Attribute type (OPT, DER, INV)
Redefinition (SELF)
Attribute / Relation
Data or Rel. type
Definition
Items
SET [1:?] OF IfcGeometricRepresentationItem
Set of geometric representation items that are defined for this representation
INV
OfProductDefinitionShape
SET [0:1] OF IfcProductDefinitionShape
Reference to the product shape, for which it is the shape representation
INV
OfShapeAspect
SET [0:1] OF IfcShapeAspect
Reference to the shape aspect, for which it is the shape representation
WR22
The IfcShapeRepresentation shall be either defined for a single product shape or for a single shape aspect.
(HIINDEX(OfProductDefinitionShape) = 1) XOR (HIINDEX(OfShapeAspect) = 1)
WR23
The context to which the IfcShapeRepresentation is assign, shall be of type IfcGeometricRepresentationContext.
'IFCREPRESENTATIONRESOURCE.IFCGEOMETRICREPRESENTATIONCONTEXT' IN TYPEOF(SELF\IfcRepresentation.ContextOfItems)
WR24
The rule constrains the supported values of representation type for this subtype in this release.
SELF\IfcRepresentation.RepresentationType IN ['BoundingBox','Standard','Advanced','Arbitrary','Brep','UserDefined','NotDefined']
WR25
Constrains the valid Items for representation according to the Shape Representation Type (IfcShapeRepTypeEnum) BoundingBox
((RepresentationType = 'BoundingBox') AND (HIINDEX(Items) = 1) AND ('IFCGEOMETRYRESOURCE.IFCBOUNDINGBOX' IN TYPEOF(Items[1]))) OR (RepresentationType <> 'BoundingBox')
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Fully Attributed View |
EXPRESS Definition |
Definition from IAI: The IfcTopologyRepresentation represents all topologically relevant information about an product, including its connectivity.
