Cost Value

A cost value represents an amount of money (the cost value) that is applied to the cost of an object. A cost value has a cost date that can be used to provide a basis on which fluctuations in price can be established or that otherwise identifies when the cost value was applied. A cost value may be assigned either a base value or a final value. These values may be asserted individually or in combination. Whilst both are optiona, at least one of these attributes must be asserted. It is intended that there should be a relation between the base cost value and the final cost value that is determined by the application of cost modifiers. However, this is not enfrced through rules in the schema. Therefore, a required relationship between the values of these attributes must be enfirced through application software. Each cost value also has a unit cost basis which determines how a total cost should be determined for items purchased. This is relevant where costs are identified per unit quantity of an item.

Cost Value Relationship

An individual cost value may be derived as the sum of a set of component cost values and may also be identified as a component of other cost values. This is achieved through the assertion of a cost value relationship which acts as a container for cost value components.

Cost Modification

A cost may be or have been modified through the application of various modifiers. Provision is made for this through the IfcCostModifier class. For instance, in determining the purchase cost of a given item, the cost from a manufacturers or suppliers price list may be subject to such factors as trade discount, bulk purchase rebate, small quantity surcharge, price list surcharge (where an old price list is used but all prices are increased by a value or percentage). Identification of which factor causes a cost modification is enabled through the purpose attribute of IfcCostModifier. The value of the cost modifier purpose needs to be set by the user; predefined purposes are not provided within the schema. A cost modifier may be applied either as a value with a defined currency (through the IfcModifierValue class) or as a value without a defined currency. Either is allowed and that to be used is selected via a SELECT data type. The selection of IfcModifierValue with its own currency may be used to inmply that the currency of the modifier is different to the currency of the cost value that it is modifying (in which case it is up to the application software to carry out any currency conversions required to determine final cost values from base cost values or vice versa). The selection of a modifier vaue of data type REAL implies that the currency is either the same as that of the relating cost value or that it is otherwise established by global assignment. In general, it is considered to be good practice to use IfcModifierValue and specify the currency even if it is the same as that of the IfcCostValue being modified.

Assigning Cost Modifiers

The IfcAssignsCostModifier class takes a defined set of modifiers and applies them to a set of cost values. Using this form of modeling construct, all cost values that are (for instance) determined from a single price list can use a single set of modifier values. If modification is not required, then the IfcAssignsCostModifier class is not asserted and there is no impact on the sharing or exchange of information.

Referencing Cost Documents

The origin of a cost value will normally be a price list, quotation or some other documentary source. The Cost Resource model allows identification of such a source through a document reference. IfcReferencesCostDocument is a relationship class that allows many cost values to be referencd from a single such document. By providing document referencing in this way, only one referenced document object need be included when sharing or exchanging such information, the object of the relationship class containing the set of all cost values that reference the document. If a document reference is not required, then the IfcReferencesCostDocument class is not asserted and there is no impact on the sharing or exchange of information.

HISTORY New schema for R2.0. This schema was formerly part of the IfcPropertyResource schema. In IFC 2x several additions have been defined to the cost resource.