Normalize (combine) equal type instances to remove redundant information

Description of the proposal:
Establish an implementation requirement to avoid redundant information in IFC containers (like IFC files) by normalization of equal type instances.
Example:
Currently exist implementations with a separate window-type definition for each window instance:
n windows of same type T => n equal window-type definitions of same type T

Proposed implementation requirement:
n windows of same type T => one window-type definition of type T

Describe how it contributes to the objectives set in https://github.com/buildingSMART/NextGen-IFC/wiki/Towards-a-technology-independent-IFC:
Reduces processing time and document (file-) size in serialized data.
Encourages normalization in databases of CDE and authoring-software thereby improving the efficiency.

What do we win:
smaller document (file-) size
reduced processing time

What do we loose
redundancy that results in oversized documents (files)

Schema impact:
none

Instance model impact:
?

Backwards compatible:
YES

Automatic migration possible:
NA

Additional implications:

-
Note that not all points need to be satisfied!
Backwards compatibility and file size are not concerns.

Start by reviewing the proposal and the linked “Towards-a-technology-independent-IFC” wiki page. Examine the stated effects on IFC containers, serialized data, databases, and the instance model; done means the normalization requirement and its compatibility and migration implications are clearly specified.

Written by the indexing model from the issue text.