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[ontolog-forum] Fw: [SPAM]RE: Fw: Thing and Class

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Cc: "[sowa@xxxxxxxxxxx]"@mccarthy.cim3.com, "[rwheeler@xxxxxxxxxxxxxxxxxxxxx]"@mccarthy.cim3.com, "[rhm@xxxxxxxxxxxxx]"@mccarthy.cim3.com, "[debmacp@xxxxxxxxx]"@mccarthy.cim3.com, "[phayes@xxxxxxx]"@mccarthy.cim3.com, "[Peter.Eirich@xxxxxxxxxx]"@mccarthy.cim3.com
From: "Sean Barker" <sean.barker@xxxxxxxxxxxxx>
Date: Mon, 8 Sep 2008 23:53:14 +0100
Message-id: <8541606C50724C2EA3361F6E8B2D1B54@PackardDesk>

Thanks for the various comments. I would rather avoid a long e-mail writing about the STEP standard, and have mostly confined comments below to issues of philosophy (however defined). Unfortunately, the STEP community are very bad at describing the philosophical background to their work, so I can't recommend any more general sources. Working back in reverse order though the various responses on the thread:
Ron Wheeler
Absolutely, do not forget support, including maintenance, upgrades and logistics. Notably, these areas require different ontological commitments to the design and manuafcturing areas, which have been much better served in terms of industrial and acaddemic analysis. Support for logistics added several subtypes to the STEP Product sutype model (see figure).
John :
Grounding the metaphysics of coming-to-be, ceasing-to-be etc is one of the major challenges of collaborative product data management. In theory, there are some common standards for configuration management, however the interpretation often comes down to particular company processes. In practice, processes are compartmentalised, and changes is treated as being in discrete steps. For example, raw materials go into the factory, component parts come out. Internally, there may be several substeps:
    A raw billet is milled to produce the part-view-definition "Condition of Supply"
    The "Condition-of-supply" is put in a jig, and the holes for mating drilled, so that it is incorporated into the first assembly - this intermediate stage is unnamed.
    The first assembly is mated to the second and the remain holes drilled creating the part-view-definition "As designed".
Conversely, a part may cease to be the instant someone designates it as scrap.
Richard H. McCullough
The attached PNG is the STEP Product subtype hierarchy. Essentially the concept of Product is defined as a concept that goes through change management controlled versions, each of which may have several views. The Type/Instance concept occurs at the level of the Product-version.
What you call characteristic would be modelled as a product-classification, and treated as data - there is nothing fundamental about it, and the classification system will vary with organization. Such classifications as "chassis" "engine" do not have a definition, but are useful heuristics, and formalisation is probably useful only within a tight-knit community.
Patrick J. Hayes
Mostly agreed. In engineering, the thing that endures is the product - of which we can say nothing except the name, and the product instance, or which nothing endures except the identity. The rest requires agreement on metaphysics.
Deborah MacPherson
Deborah - there are data models in the building industry which are the equivalent of STEP. Combining these with the PLCS approach of using the STEP data model to provide structure and set of taxonomies for the structure of the concepts within the data structure may be one way of doing this
Eirich, Peter
Agreed, which is why STEP allows multiple breakdowns and multiple views. Multiple breakdowns allow for the same parts to have different functions, so that the ribs and stringers of an aircraft wing define the structure of the wing, however they also turn up as the edges of the fuel tanks in the fuel system - an aircraft fuel tank is a functional subsystem containing no parts. However, multiple breakdowns are not enough, you also need multiple views. A wiring loom is a physical collection of wires, taking a particular shape, and it is also a component in multiple electrical systems. The accidents of the placement of electrical components are of little interest to the system designers, but are key to the physical structure designers.
You might also note that the STEP model also deals with interfaces, connectors and slots (places where components occur), and there are already very extensive models of electrical, electronic and electro-mechanical systems in STEP.

Sean Barker
Bristol, UK
+44(0) 117 302 8184

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