Formal Definition
ISO 15926-2:2003 is a part of ISO 15926, an International Standard for the representation of process plant life-cycle information. This representation is specified by a generic, conceptual data model designed to be used in conjunction with reference data: standard instances that represent information common to a number of users, process plants, or both. The use and definition of reference data for process plants is the subject of Parts 4, 5 and 6 of ISO 15926
What does that mean ?
Part 2 describes THE fundamental entities to which ALL future entities must relate to. The definitions in part 2 are not specific to any industry, but is sufficient to enable all domain specific entities to be described.
The actual Plant items are defined in Part 4 and will ALL relate back to a part 2 entity ...
A quick scan of Part 4 shows that PUMP is indeed defined as a SPECIALISATION of a POSSIBLE INDIVIDUAL
In short ... Part 2 is a rigid set of terms that cannot be added to and which must be used to describe items in Part 4
Is this available online ?
Yes, there is an online version of ISO 15926 Part 2
http://www.tc184-sc4.org/wg3ndocs/wg3n1328/lifecycle_integration_schema.html
Will ISO 15926 Part 2 change ?
No fundamentally Part 2 should not change as this is the considered building blocks.