Teamcenter - What is the difference betweeen Precise & Imprecise assemblies?

If you work with BOMs in Teamcenter you have probably seen the terms Precise and Imprecise BOM structure. Even if you only use one type of BOM you need to understand the difference between them.

BOM View Revisions

In Teamcenter an assembly structure is represented by a BOM View. BOM Views are associated with Items, and each Item Revision will have it’s Revision of the BOM View — a BOM View Revision, or BVR.

The descriptions precise and imprecise apply to BOM view revisions. It is determined by an attribute of the BOM view revision business object.

What does Precise and Imprecise BOM Mean?

A BOM View Revision defines which components are used by a particular Item Revision. precise and imprecise describe what is meant by component. If a BVR is precise the components are item revisions; the BVR defines precisely which revision is used by the structure. If the assembly is imprecise the components are items; the BVR is not precise about the revision to which the assembly refers.

Why Precise Structures are Important?

When you release an assembly, releasing the precise structure preserves the record of exactly what it was that was developed, approved and released. It is an important historical artifact, particularly of the CAD data.

Why Imprecise Structures are not Important?

Imprecise Assemblies can be used in Industries where there is no concept of Revisions.

For Example:  In Retail Industry there will not be any concept of Revising the Assembly (ex: Shirt Assembly). They will save as and create a new Shirt for the next season. In those cases I think Imprecise Structure concept is apt.

Precise and Imprecise Assemblies

We start the examples with four component items with two revisions, 01 and 02, of each. Each revision may be Released, meaning it has a status, or working, meaning it has no status.

                                                                              

Next, we have two assemblies which both use these four components. The first, IMP-100, has an imprecise assembly structure, while the second, PRE-200, has a precise assembly structure.

Assembly with an Imprecise structure

                   

* The imprecise assembly stores references to items not item revisions and they are dynamic.

Assembly with a Precise structure

* The precise assembly stores references to specific item revisions, not items. In this case it refers to revision 01 of each of its components. The precise assembly has static structure.