Identification of Express Version

[Phil Spiby]

Pascal,

The main intent with this is to support the schema developers.
It would be nice to think that all EXPRESS parsers supported the latest
version, in that case I guess we could do away with this mechanism. However,
life is not like this!

As the author of a schema you decide what you want to capture in your model,
and which constructs of EXPRESS you are going to use. As a result you
control which version of EXPRESS you are using. To assist people working
with you, or using your model it is, our belief, useful to inform them
formally which version of EXPRESS you have used. If you do not then it is
highly likely that you will receive complaints that your model is wrong
since others will undoubtedly use different tools to verify the model that
you have used.

I know this happens through personal experience. I was writing a model for a
customer, and one of the constraints required TC2 level support. The EXPRESS
toolkit they was using rejected the constraint and refused to build the
required data structures. As a result the customer, knowing that I knew
EXPRESS pretty well, asked me to contact the support desk of their EXPRESS
toolkit vendor. On doing this I was told that this was the expected
behaviour, and that the construct I had used was wrong. Further more could
they help by providing EXPRESS training to me, since I was obviously in need
of it!
I was able to sort things out fairly quickly by calling the person from the
vendor company who attends ISO meetings, and the parser was changed.

For many people they need the confidence in the tool that is does support
the EXPRESS they have written, although this is not guaranteed by this
approach, it should allow tools which do not support the latest version to
be easily identified.

Phil

  -----Original Message-----
  From: Pascal Huau [mailto:pascalhuau at goset.asso.fr]
  Sent: Monday, May 06, 2002 10:04 AM
  To: Phil.Spiby at eurostep.com
  Cc: WG11
  Subject: Re: Identification of Express Version


  Dear all,


  I would like to add my two cents (of Euro) in the debate.


  Q1: Is it needed to indicate the version of the Express language in an
Express schema?

  If I am the customer of an application, the answer to Q1 is no. (If I am
expert enough to know that there are several versions and TCs of Express) I
want to know which version and TC of Express, the application implements and
the marking of Express schemas does not provide me any information about
that.

  If I am developer of an Express application, the answer is also no.
  Either my application implements the latest version of the language or it
does not.
  If it does not,  then it will return an error when it encounters an
Express language construct (e.g. extensible select) that did not exist in
the version of the language that was considered at design of my application.
  If it does, then the application will hopefully recognize all language
constructs. As long as upward compatibility is kept in the specifications of
Express language, these constructs can be interpreted correctly by the
application, whatever they are old or new constructs.
  So the actual question to answer is:
  Q2: is Express2 upward compatible with respect to Express1? Are all the
Express1 constructs still valid in Express2? Is there any restriction in
their specification that has been introduced in Express2?


  Regards,
  Pascal Huau
  Association GOSET
  107,111 avenue Clemenceau
  92000 Nanterre
  France
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