ISO/IS 10303-51:2005 specifies the integrated resource
Mathematical representation.

ISO 10303-51 constrains the use of the concepts of mathematical value that are defined by ISO 10303-50. The uses are specified
as follows:

• that a real or integer number identifies a physical quantity instance, or a product, activity or state;
• that a mathematical space is the range of an an identification function for a physical quantity space, or a set of products,
  activities or states;
• that mathematical function describes a property variation over a continuous or discrete domain.