Already some time ago (early 2020) the article Has FFF Killed? from Yoann Maingon has generated a lot of discussion, already 100+ comments and counting. It is clear there is a lot of opinions about how to deal with changes to parts, whether parts have revisions or not, and how PLM tools should deal with this. So what better way to start they new year, with a blog post on Parts and Revisions!
Parts and revisions
I think we can all agree, and even most experts, professional literature and standards are clear on this: Parts do not have revisions. As stated on buyplm.com:
One part number = one bin location. Revision is irrelevant.
So why do PLM tools have revisions for parts?
Well in many PLM tools some of the meta data is stored on the revision of the part and also the Bill of Material and relations to documents and other objects depart from the revision of the part.
So what does this mean? Does a part have a revision or not?
Look at it this way: A part number is a reference to a thing in the ‘physical’ world. Parts are described by datasets. Datasets can be documents or structured data and datasets have revisions.
Dataset: A set of information stored in digital or physical form that must be released as a whole and can be released separately from other datasets.
The problem though is that, in a lot of systems, not each dataset is uniquely identified and does not carry its own revision. To efficiently change part documentation, it is required that each dataset has its own number and revision in order for it to have its own life cycle. That means the Bill of Material, CAD Model and the metadata of a part must have their own number and revision, which is often times not the case.
How should you link a dataset to a part?
If you look back at the definition of a dataset, you can read that changing one dataset can be done without impacting the other dataset. This creates change agility in a system. Now I can have multiple changes being implemented at more or less the same time, on different datasets for the same part without interfering or delaying other changes.
Linking datasets to parts should be done with a relationship and is either done by a relation between part and dataset ‘master’ or if you still have a part revision, between part revision and dataset ‘master’. This will limit overlapping changes. Also read the article: What the FFF is happening? by Jos Voskuil.
An example of a (simplified) data model using master-revision concept for datasets and parts are without revisions:
As you can see in this data model, parts do not have revisions, but all the datasets do have revisions. I even separated the CAD part from the part itself. This allows to have an evolution of parts like P2 being superseded by P4, which is captured by the same CAD Part dataset but different revision of that dataset. I can now for instance change the metadata of part P1, without having to revise the BoM (Bill of Material). That does not mean you can only solve this through a data model, but this is a way to do it.
Dataset/Document centric or Object/relation centric?
It is not either or, you need both because each have a different purpose. Impact analysis requires both approaches to be supported. For CM you need to identify impacted datasets to be able to estimate cost of a change in order to come to a business decision and to be able to plan deliverables for implementation of the change. However CM2, from the Institute of Process Excellence, also explains that information needs to be structured linked and owned, while not all of the objects and linkages are part of the CM level impact analysis, these are important for the experts in the expertise domains that have to assess the impact of a change, come up with a solution and in the end create or update this information.
See also some of my previous articles A glimpse into the future of CM and We need a cross platform interface for Impact Analysis, where I highlight the difference between the different levels of dealing with information. You do not plan the update of a single bomline, you plan the update of an entire Bill of Materials in the context of a change. But the expert needs to know exactly what the impact of the change will be. However for planning the change typically knowing you need to update a Bill of Material, a 3D model, a test plan, a process plan or a work instruction is enough to estimate the amount of work and cost involved. But for execution of the work and for understanding the solution needed, it is critical that you need more than just a dataset. Here structured data will be important to understand the impact. You need both and a PLM system needs to support both.
Header photo by nikko macaspac on Unsplash