Question 1
What is a Conformance Class?
Answer to Q1
A Conformance Class (CC) is a valid subset of the LPM/5 EXPRESS schema. A CC
is specified as a short form EXPRESS schema using STEP schema interfacing. The
CC schemas contain no entity or type declarations, merely the USE FROM and the
REFERENCE FROM declarations. All the entities referred to in a CC schema are
declared in the 'structural_frame_schema'; i.e. the LPM/5 long form schema
documented in Volume 4.
If instances of these entities were created and their attributes correctly
populated, the set of data produced would be coherent and valid, and if it were
exported from the STEP data repository, a valid STEP Part 21 file should result.
At the same time, information conforming to a CC is compatible with the complete
LPM/5 schema.
Question 2
What is the purpose of a CC?
Answer to Q2
The primary purpose of a CC is to test a particular CIS implementation for
conformance to the CIS/2 standard. For each CC, or combination of CCs, a number
of test cases can be generated and used during formal Conformance Testing. The
LPM/5 long form EXPRESS schema is an extremely large and complex 'Product
Model'. Moreover, LPM/5 is not a simple hierarchy of 'classified types' but a
network of interrelated 'entity objects' that may be populated in many different
ways to reflect their information content.
Although it is theoretically possible to define CCs for each and every
permutation of the possible populations of the LPM, it would not be practical to
do so, as it would result in the creation of several hundred thousand CCs. The
creation of 'modular' Conformance Classes was seen to be the more realistic
approach. These modular CCs are then put together as required for implementation
and testing.
Put simply, LPM/5 is far larger in scope and has a much greater range of
functionality than any existing engineering software application. Thus, it is
highly unlikely that any application vendor would implement the LPM/5 EXPRESS
schema in its entirety. Furthermore, data is generally exchanged in relatively
small packets. Given the life cycle of a steel structure, large exchanges of
'complete' models will be rare.
Therefore, LPM/5 has been broken down into smaller manageable pieces. These
pieces - the CCs - may be combined like building blocks in many different ways
to define a specific collection of information. CCs may also be used
(individually or in combination) to formally describe the scope of a
CIS/2-compatible application, and its translator.
Obviously, the scope of the application will be greater than that of an
individual CC, but the information that the end users will wish to share will
fit into one or more combinations of CCs. The vendor of the engineering software
application seeking CIS/2-conformance is at liberty to choose how the CCs are
combined.
Although CCs may be used to formally define the scope of an exchange file,
most engineering end-users will not need to know the details of CCs. All they
need to be assured of is that when dealing with applications that have
overlapping sets of CCs, some useful data exchange is possible.
Question 3
Why does CIS/2 use CCs?
Answer to Q3
CIS/1 used the concept of Data Exchange Protocols (DEPs) and defined four
DEPs to cover broad areas of analysis, member design, connection design and
detailing. Unfortunately, these DEPs proved to be too broad in scope and too
flexible on implementation to allow the enforcement of rigorous testing. CIS/2
uses the approach to implementation and testing that is used by STEP; i.e.
Conformance Classes (CCs). This is one of the significant differences between
CIS/1 and CIS/2, a difference which has had a major influence on the size and
style of the data model for implementation (LPM/5). Since CCs are defined and
tested at an entity level (rather than at the attribute level of a DEP), a
CIS/2-compatible system is required to support all the attributes of all the
entities within a CC.
Question 4
Shouldn't all conformance classes be listed in the header section of the
physical file?
Answer to Q4
Page 112 of Publication SCI-P-269 states...
