|
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
Ron:
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
Dick:
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
Pat:
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
| 