Persistent IDs

Persistent IDs are identifier strings or integers attached to entities. However, not all entities have persistent IDs. This depends on the format. HOOPS Exchange supports the concept of persistent IDs for certain file formats. Persistent IDs are important for developers drawing data from many CAD systems, since IDs assigned to model entities are persistent across different sessions.

Persistent IDs are stored as a field in the A3DRootBaseData structure as either a string A3DRootBaseData.m_pcPersistentId or an integer A3DRootBaseData.m_uiPersistentId. This attribute could be retrieved from rootbase data, with an additional way for assembly members by using A3DAsmProductOccurrenceGetIdentifier().

The persistent ID assigned to an entity will be defined by the CAD format. For HOOPS Exchange, ensure that each time the same file (or any version of the same file) is read so that any entity will have the same identifier previously defined. Typically, this confirms that any entities found with IDs matching between multiple files are in fact the same entity.

It is important to note that these IDs are not guaranteed to be unique. For instance, there are some cases where entities like faces can have the same ID. For example, this could happen when a feature groove is applied to define a body. More specific information on an example like this can be found in the table below. Navigate to any of one of these formats and sections to see these details: Inventor, CATIA, or SLW’s rows regarding the column Splitting a face - Adding a Groove.

Below is a table that provides information on how HOOPS Exchange supports persistent IDs across different formats and several different topological entity modifications. Each tab within each format section describes a different modification of a cube part and how the persistent IDs are effected based off of the changes described. They include image examples of each type of modification occuring to the part.

Formats and their Modification Supports

CATIA

This section describes what happens to the persistent IDs for parts in the CATIA file format with different part modifications.

Adding a loop to a face - Extruding a hole into a cube

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a loop to a face, ie. extruding a hole into the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

Faces

Edges

New

2 faces with same persistent ID

(CATIA split cylinder)

4 edges

Changes

none

Adding a face to the model - A chamfer

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a face to the model, ie. adding a chamfer to the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

Faces

Edges

New

1 face

8 edges (see modified image above)

4 for the chamfer face

4 for the cut edges

Changes

none

1 edge is removed

4 edges are cut, so the persistent ID will change

Splitting a face - Adding a groove

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a face to the model, ie. adding a uniform groove into the side of the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

Faces

Edges

New

3 faces

14 edges (see modified image above)

10 for the new faces

4 for the cut edges

Changes

1 face is cut (split) in two. Both have the same persistent ID (see original picture above)

1 edge is removed

4 edges are cut, so the persistent ID will change

Have cylinder srf split - Adding a hole through a groove

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by having a cylinder srf split ie. adding a hole through a groove.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	4 faces, with the same persistent ID	6 edges
Changes	none	none

Unicity of IDs - Hole repitition

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, we have a unicity of IDs ie. a repitition of holes extruding into the cube in parallel.

Original cube part	Modified cube part

In the CATIA file format, a hole repitition will create 6 faces with different persistent IDs (2 faces per hole).

Editing a feature

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, we have an edit to a feature ie. the cube was transformed into a rectangle.

Original cube part	Modified cube part

In the CATIA file format, editing a feature can change persistent IDs.

Editing a sketch

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, an edit to the sketch of the part was made.

Original cube part	Modified cube part

In the CATIA file format, editing a sketch will recompute ALL of the persistent IDs.

Creo

Adding a loop to a face - Extruding a hole into a cube

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a loop to a face, ie. extruding a hole into the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	1 face (cylindrical)	2 edges (see modified image above)
Changes	none	none

Inventor

Adding a loop to a face - Extruding a hole into a cube

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a loop to a face, ie. extruding a hole into the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	1 face (cylindrical)	2 edges (see modified image above)
Changes	none	none

Adding a face to the model - A chamfer

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a face to the model, ie. adding a chamfer to the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

Faces

Edges

New

1 face

8 edges (see modified image above)

4 for the chamfer face

4 for the cut edges

Changes

none

1 edge is removed

4 edges are cut, so the persistent ID will change

Splitting a face - Adding a groove

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a face to the model, ie. adding a uniform groove into the side of the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

Faces

Edges

New

3 faces

14 edges (see modified image above)

10 for the new faces

4 for the cut edges

Changes

1 face is cut (split) in two. Both have the same persistent ID (see original picture above)

1 edge is removed

4 edges are cut, so the persistent ID will change

Have cylinder srf split - Adding a hole through a groove

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by having a cylinder srf split ie. adding a hole through a groove.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	2 faces, with the same persistent ID (see modified image above)	4 edges
Changes	none	none

Editing a feature

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, we have an edit to a feature ie. the cube was transformed into a rectangle.

Original cube part	Modified cube part

In the Inventor file format, editing a feature does not change any persistent ID.

Editing a sketch

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, an edit to the sketch of the part was made.

Original cube part	Modified cube part

In the Inventor file format, editing a sketch will have no effect if the semantic does not change:

Editing segment length: Does not change any persistent IDs

Replacing a segment by a curve will change persistent IDs as follows:

Faces

Edges

New

1 face (see original picture above)

7 edges

Changes

1 face is changed

Only 5 edges are kept (see modified image above)

Edges of the sketch are changed

Projected edges not linked to the curve are kept

NX

Editing a sketch

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, an edit to the sketch of the part was made.

Original cube part	Modified cube part

In NX file format, editing a sketch will have no effect if the semantic does not change:

Editing a segment length: Does not change any persistent IDs

Replacing a segment: New faces and ALL associated edges will have new persistent IDs

SLW

Adding a loop to a face - Extruding a hole into a cube

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a loop to a face, ie. extruding a hole into the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	1 face (cylindrical)	2 edges (see modified image above)
Changes	none	none

Adding a face to the model - A chamfer

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a face to the model, ie. adding a chamfer to the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	1 face	4 edges for the chamfer face
Changes	none	1 edge is removed

Splitting a face - Adding a groove

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a face to the model, ie. adding a uniform groove into the side of the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	3 faces	10 edges, for the new faces
Changes	1 face is cut (split) in two. Both have the same persistent ID (see original picture above)	More info coming soon

Have cylinder srf split - Adding a hole through a groove

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by having a cylinder srf split ie. adding a hole through a groove.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	2 faces, with the same persistent ID (see modified image above)	4 edges
Changes	none	none

Unicity of IDs - Hole repitition

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, we have a unicity of IDs ie. a repitition of holes extruding into the cube in parallel.

Original cube part	Modified cube part

A hole repitition (with pattern feature) will create 3 faces with different persistent IDs (1 face per hole).

Editing a feature

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, we have an edit to a feature ie. the cube was transformed into a rectangle.

Original cube part	Modified cube part

Editing a feature does not change any persistent ID.

Editing a sketch

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, an edit to the sketch of the part was made.

Original cube part	Modified cube part

In NX file format, editing a sketch will have no effect if the semantic does not change:

Editing a segment length: Does not change any persistent IDs

Replacing a segment: New faces and ALL associated edges will have new persistent IDs

UG

Adding a loop to a face - Extruding a hole into a cube

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a loop to a face, ie. extruding a hole into the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	1 face (cylindrical)	2 edges (see modified image above)
Changes	none	none

Adding a face to the model - A chamfer

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a face to the model, ie. adding a chamfer to the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	1 face	4 edges for the chamfer face
Changes	none	1 edge is removed

Splitting a face - Adding a groove

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by adding a face to the model, ie. adding a uniform groove into the side of the cube.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

Faces

Edges

New

4 faces

12 edges

10 for the new faces

2 for one part of the cut edges

Changes

1 face is cut (split) in two. Both have the same persistent ID (see original picture above)

2 edges are cut in two. Edges on one side will have new persistent ID

Have cylinder srf split - Adding a hole through a groove

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, the part was modified by having a cylinder srf split ie. adding a hole through a groove.

Original cube part	Modified cube part

See below for what’s new to the part after modification, and any possible changes that may have occurred and altered any persistent IDs to the part file.

	Faces	Edges
New	2 faces, with different persistent IDs	4 edges
Changes	none	none

Note

With the hole feature, if at some point we edit a feature to merge the 2 holes into one face, the resulting face persistent ID / color / properties will be taken from the farthest face from the origin of the hole.

Unicity of IDs - Hole repitition

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, we have a unicity of IDs ie. a repitition of holes extruding into the cube in parallel.

Original cube part	Modified cube part

In the NX file format, a hole repitition will create 3 faces with different persistent IDs.

Editing a feature

In this model modification, we see the original, unaltered cube on the left and the altered cube on the right. In this instance, we have an edit to a feature ie. the cube was transformed into a rectangle.

Original cube part	Modified cube part

Editing a feature does not change any persistent ID.

Immutable Persistent ID Instances: Assembly Cases

There are also several instances where the persistent IDs should never change. Read through the tabs below to see example details and images.

Base assembly

Persistent IDs should never change during base assembly. For example, notice in the image that several previously created CAD parts are being assembled to form a completed CAD product. Any manipulation of parts or objects during the assembly should never cause any change to a previously defined identifier.

Changing order of components

Persistent IDs should never change if and when you change the order of components in an assembly model tree.

In the images provided below, we see a CAD assembly file that consistents of several CAD parts. Originally, the model tree reads the chronological order of cylinder 1, cube 1, and finally cube 2, as seen in the original order of components image on the left. Note in the Modified order of components image the changes to the parts order in the model tree structure. It now instead chronologically lists in the model tree the parts as cube 2, cube 1, and then cylinder 1.

Original order of components	Modified order of components

Despite these changes in the model tree parts structure, the persistent IDs of any entities in any of the parts should remain the same.

Removing components

Persistent IDs should never change if and when you remove any components from an assembly file.

In the images provided below, we see a CAD assembly file that consistents of several CAD parts. Originally, the model tree reads the chronological order of cylinder 1, cube 1, and finally cube 2, as seen in the original components in assembly image on the left. Note in the Components in assmebly after cube 1 removal image the removal of cube 1 from the assembly file in the model tree structure. It now instead chronologically lists in the model tree the parts of the file to now contain only cylinder 1 and cube 2.

Original components in assembly	Components in assembly after cube 1 removal

Despite the removal of a part from the assembly file, the persistent IDs of any entities in any of the parts should remain the same.

Editing component parameters

Persistent IDs should never change if and when you edit any component parameters from within an assembly file.

In the images provided below, we see a CAD assembly file that consistents of several CAD parts. Originally, the model tree reads the chronological order of cylinder 1, cube 1, and finally cube 2, as seen in the original components in assembly image on the left. We can see in the image that the cylinder is blue, and the two cubes are green. Note in the Modified component parameters of cube 2 in assembly image that the component parameters of cube 2 has been altered. Rather than green, cube 2 is now yellow.

Original components parameters of assembly parts	Modified component parameters of cube 2 in assembly

Despite editing the component parameters of cube 2, the persistent IDs of any entities in any of the parts should remain the same.

Other Format Information

File Type	Assembly Nodes	Solids	Faces	Edges	Density
CATIA V5	Persistent ID string (CLSID)	Persistent ID integer (key)	Persistent ID string as attribute (string)	Persistent ID string as attribute	In ProductInformation (for each occurrence corresponding to a file)
Creo/Pro-E	Persistent ID string (CLSID)	Not applicable	Persistent ID integer (key) - Note: Persistent ID inside a part are different even when there are several solids.	Persistent ID integer (key) - Note: Persistent ID inside a part are different even when there are several solids.	Latest versions of Creo have them. Otherwise, we put the stored filename.
NX	Persistent ID string (CLSID)	Persistent ID integer (key)	Persistent ID integer (key)	Persistent ID integer (key)	In ProductInformation (for each occurrence corresponding to a file)
SolidWorks	Persistent ID string (CLSID)	Persistent ID integer (key)	Not applicable	Not implemented	In ProductInformation (for each occurrence corresponding to a file)
JT	Not applicable	Not applicable	Not applicable	Not applicable	In ProductInformation (for each occurrence corresponding to a file)
SolidEdge	Persistent ID string (CLSID)	Persistent ID integer (key)	Persistent ID string as an attribute	Not implemented	In ProductInformation (for each occurrence corresponding to a file)
Inventor	Persistent ID string (CLSID)	Persistent ID integer (key)	Persistent ID string as an attribute	Not implemented	In ProductInformation (for each occurrence corresponding to a file)