Index Page

  Specification for IfcDocumentExtension  

EXPRESS Definition

EXPRESS-G Diagram

IDL Definition

Schema Semantic Definition

The IfcDocumentExtension schema contains model specifications for specifying the information content of a NUMBER of typical document types encountered within building construction.

Presently, only one type of document is contained within the schema, namely cost schedules, which can comprise cost elements. The following apply:

• A cost schedule provides a means of aggregating costs so that they can be described fully on a line on a costing document (or cost sheet). Elements can be grouped together so that their cost as a group can be captured as well as their individual element cost. The cost of the complete schedule can also be captured. The cost schedule allows for such information as who was responsible for its preparation, approval and submission to be captured so that this information can be provided with the schedule.
• The items in the cost schedule are represented by IfcCostElement that is capable of containing other IfcCostElement(s).
• No mathematical operations are allowed within the model for cost scheduling. Thus, although the cost of a nested cost element is the sum of the cost of its sub-elements that make up that nest, it is the responsibility of the application to provide that information and not the model to derive it.

Class IfcCostElement

EXPRESS Definition

Class Semantic Definition

IfcCostElement is a cost with context information. It represents goods, services, or the execution of works of a described elemental nature in given conditions. This entity also has the capability of nesting other items of the same type (i.e. IfcCostElement) through its relationships to IfcRelNestsCostElement.

The relationship to costed products (IfcProduct) determines the NUMBER of IfcProduct objects which are costed by an IfcCostElement. However, this relationship does not determine the quantity to be used in a cost schedule. Each IfcProduct object may contain a quantity component that needs to be added to other quantity components to establish the value to be assigned to the Quantity attribute. It is this value which is used in extending the cost to give the Extension Cost.

The following figure shows an elementary cost element:

The next figure shows how elementary cost elements can be grouped into cost groups, represented by cost elements being nested within another cost element (using the IfcRelNestsCostElements objectified relationship).

Attribute and Relationship Definitions

Inherited Classes

Attributes and Relationships

	Attribute / Relation	Definition	Data or Relation Type	Min	Max	Default
OPT	ContextDescription	Descriptive text applied to a cost schedule element.	STRING	see type	see type	empty
OPT	ElementCost	The cost of a single item or unit of product as determined by the basis measure and basis quantity for costing. NOTE - Element cost may be either a unit cost or an item cost depending upon how the product is costed and/or purchased.	IfcCost	see type	see type	NIL
OPT	ExtensionCost	The total cost of the element when the item cost is multiplied by the quantity.   NOTE - Note that at this level of the model, no distinction is made between labour cost and material cost. Nor is any specific provision made for detailing of the element in terms of identification of additions for overheads and profit (which may be dealt with via the cost class).	IfcCost	see type	see type	NIL
OPT	PreparedOn	Date on which a cost schedule group was prepared.	IfcDateTimeSelect	see type	see type	empty
OPT	Quantity	The total quantity of items to be costed as an element. NOTE - The quantity is derived by adding together the amount of product according to the basis measure and basis quantity identified within the cost model. It may be the NUMBER of units, total length, area or volume or other measure.	NUMBER	see type	see type	Empty
INV	PartOfCostSchedule	Reference to the Cost Schedule, in which the Cost Element is contained.	Set [0:1] IfcCostSchedule	0	1	1
INV	CostsProducts	Products which are included within the Cost schedule	Set[0:1] IfcRelCostsProducts	0	1	0

Formal Propositions:

WR41	Restrict the relationship 'Nests' inherited from IfcObject to IfcRelNestsCostElement.
WR42	Restrict the relationship 'IsNestedBy' inherited from IfcObject to IfcRelNestsCostElement.

Interface Definitions

• I_CostElement

Type Definitions

This class is not typed -- there is no type definition.

Class IfcCostSchedule

EXPRESS Definition

Class Semantic Definition

A document that provides a schedule of costs. The cost schedule contains cost elements, which can be nested to represent cost element groups.

Attribute and Relationship Definitions

Inherited Classes

Attributes and Relationships

	Attribute / Relation	Definition	Data or Relation Type	Min	Max	Default
	ScheduleTitle	Title given to the complete cost schedule.	STRING	see type	see type	n/a
OPT	SubmittedBy	Identity of the person or organisation submitting the cost schedule.  NOTE - Submission of the cost schedule may be by a person or an organisation.	IfcActorSelect	see type	see type	NIL
OPT	ApprovedBy	Identity of the person approving the cost schedule. NOTE - Approval implies that the cost schedule has been checked and approved by a person within the organisation that is submitting.	IfcPerson	see type	see type	NIL
OPT	PreparedBy	Identity of the person preparing the cost schedule.	IfcPerson	see type	see type	NIL
OPT	SubmittedOn	Date on which a cost schedule was submitted.	IfcDateTimeSelect	see type	see type	NIL
OPT	Cost	Cumulative cost of a cost schedule.	IfcCost	see type	see type	NIL
	HasCostElements	Relationship to the Cost Elements that are included in the schedule.	List [1:N] IfcCostElement	see type	see type	n/a

No formal and informal propositions defined at this level.

Interface Definitions

• I_CostSchedule

Type Definitions

This class is not typed -- there is no type definition.

Class IfcRelCostsProducts

EXPRESS Definition

Class Semantic Definition

This entity establishes a one to many relationship between IfcCostElement and IfcProduct, so that an instance of IfcCostElement can be associated with instances of IfcProduct.

Attribute and Relationship Definitions

Inherited Classes

Attributes and Relationships

	Attribute / Relation	Definition	Data or Relation Type	Min	Max	Default
	RelatingCostElement	Points to the cost element that costs the products.	IfcCostElement	see type	see type	n/a
	RelatedProducts	Product or list of Products which are costed.	List [1:?] IfcProduct	see type	see type	n/a

No formal and informal propositions defined at this level.

Interface Definitions

• I_RelCostsProducts

Type Definitions

This class is not typed -- there is no type definition.

Class IfcRelNestsCostElements

EXPRESS Definition

Class Semantic Definition

This entity provides a model mechanism to allow IfcCostElement to contain other items of the same type. It is a subtype of IfcRelNests defined in the Kernel schema and it provides the relationships between the nesting IfcCostElement and nested IfcCostElement(s).

NOTE: This is a new class in Release IFC 1.51.

Attribute and Relationship Definitions

Inherited Classes

Attributes and Relationships

	Attribute / Relation	Definition	Data or Relation Type	Min	Max	Default
OPT	NestingDescription	Descriptive text to provide basic information about the nesting	STRING	see type	see type	empty
OPT	NestingCriteria	A description of how the items are nested into one aggregated cost element.	STRING	see type	see type	empty

Formal Propositions:

WR31	Nesting item must be of type IfcCostElement
WR32	Nested items must be of type IfcCostElement

Interface Definitions

• I_RelNestsCostElements

Type Definitions

This class is not typed -- there is no type definition.