[step-manufacturing] AP 242e4 UUID status

[Thomas Thurman]

Dear Martin,
Here is a short summary of the progress on the AP 242 information model UUID effort.
We anticipate a ballot on this during the fall.

See associated Jira issue
https://sd.iso.org/jira-pilot/browse/TCSC410303-14

Best Regards,
Tom Thurman

Status report:
Good progress has been made on basic application of UUID to a single record in a STEP data set.
We are ready to request a module part number from ISO, as we need to deliver a model for AP 242e4.
For MCAD, we are expecting that CAD software implementors attach a UUID attribute to a node in the source model tree. This aligns with the Hybrid model effort led by Ben Urick <https://sd.iso.org/jira-pilot/secure/ViewProfile.jspa?name=benurick%40nvariate.com>. For the single target record use case, we are proposing directly specifying either a identification_item SELECT or a id_attribute_select SELECT. (It is noted that the consequence of this decision is that we will need to deal with the mapping specification issue of multiple assertions involving identfication_item.)
 
We are currently investigating how to address aggregate use cases:
connected instance graph where the pre-processor can infer association
e.g., using a shape_aspect as a pseudo-root node with multiple records referencing it as defined by an entry in a mapping specification.
Using a property_definition as a pseudo-root node with a sequence of records associated to it as defined in a mapping specification
The model does not formally specify a mapping specification but is a possibility to investigate in the future is the approach of specifying an ARM AO as a target. That would require a formal mechanism for referencing an AO which does not currently exist in STEP from an AIM data set. 
Where there is a CAX-IF instance data requirement specified that can be reference by e.g., recommended practice name, version, clause.
Dis-connected instance graph where an external pre-processor specifies an aggregate for a business purpose based on an exchange agreement.
It is noted that representation is a strong containerization concept in STEP.
It is noted that item_identified_representation_usage (IIRU) provides the ability to subset a representation.
Current trade studies include:
structural options for aggregate use case (there is a uniqueness constraint that only  one instance of UUID can reference an item of product data). Each of the following options addresses the requirement for a shape_aspect as an aggregator node in the STEP model while permitting supporting the single item use case.
Define the UUID identified items as a recursive structure of UUIDs that specify a LIST of records at the tail 'call'
Define the UUID identified items as a LIST OF LIST of records
Integrate a merkle tree (see wikipedia and the THEX exchange format) with the UUID attribute structure. (The leaf nodes of a merkle tree point to a data record). It is anticipated there will be multiple merkle trees in an exchange data set.
A merkle tree model that appears to be compliant to the THEX exchange model has been created
Naive model integration with the UUID model increases instance count because the UUID is an instance and the merkle tree node is an instance
Fully integrated model has complex SUBTYPE graph (to cover corner cases)
Merkle trees can be costly to create when data sets are large.
Hash functions are agreed to be user defined and reference to the hash function is exchanged.
The UUID function is called after the hash is created.
Cryptographic hash functions can be applied that may alter the cost-benefit ratio but encrypting the STEP data is not currently in scope of this issue.
Historically, the STEP pre-processors have strongly aligned with the principle that only data that exists in the internal CAD model shall be converted to STEP product data. Adding the single UUID to a STEP record is non-controversial and sought after by multiple parties and is moving forward. Neither of the two aggregate options are part of current practice.
Comments by parties identified as watchers on this issue are solicited. Feel free to send direct email to Thurman Tom Mr <https://sd.iso.org/jira-pilot/secure/ViewProfile.jspa?name=thomas.r.thurman%40imonmail.com> or attach comments to the issue.

> On Jun 21, 2023, at 6:21 AM, Martin Hardwick <hardwick at steptools.com> wrote:
> 
> hardwick at steptools.com has invited you to UUID Management across distributed systems
> 
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