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Subject: Re: Minor versioning; was: [ubl] Discussion of substitution groups


I think Tony's email here is a good point to
pick up on any further discussion of minor
versioning without losing the threads of
what was discussed for (now obsolete) 1.1


----- Original Message ----- 
From: "Anthony B. Coates" <abcoates@londonmarketsystems.com>
To: <ubl@lists.oasis-open.org>
Sent: Wednesday, July 20, 2005 9:07 AM
Subject: Re: [ubl] Discussion of substitution groups

> On Mon, 18 Jul 2005 16:08:50 +0100, CRAWFORD, Mark <MCRAWFORD@lmi.org>
> wrote:
> > But if our schema follow our NDRs and are created from models as
> > expressed in the spreadsheets, why do we need to use substitution groups
> > at all?
> Sorry I'm a little late in responding to this thread.  In the SSC group,
> we spent a lot of time, during the UBL 1.1 days, looking at pros and cons
> of different methods of managing minor versioning.  In particular, we were
> looking at ways of being able to provide some reasonable proof or
> guarantee that a new minor version of the UBL Schemas really is backwards
> compatible with the previous major/minor version.  Before we finished this
> discussion, it was decided that we would skip 1.1. and go straight to 2.0,
> so we never really brought this discussion back to the main group.
> There are two key issues around backwards compatibility: how does UBL
> satisfy itself that new minor version Schemas are backwards compatible,
> and how does UBL convince its users that new minor version Schemas are
> backwards compatible?  The latter is the more difficult question.
> Although the UBL models (spreadsheets) are the source of the definitions,
> the Schemas are the deliverable that users really use, so it is at the
> Schema level that users will judge whether the Schemas appear to be
> backwards compatible.  The one advantage that the Scheme
> extension/restriction/redefine/substitution constructs have is that they
> make explicit how the new Schema version is derived from the previous one,
> so you only have to examine the changes to assess backwards
> compatibility.  If you just generate the full Schemas anew each time, you
> get into the difficult area of trying to do diffs between full Schemas,
> something that tools don't give you any help to do (none that I've seen,
> anyway).
> Mind you, generating minor version Schemas as "deltas" on top of the
> previous major/minor version isn't without some problems either, since it
> suggests that the spreadsheets also need to express deltas, and that isn't
> entirely straightforwards either, particular if you have multiple minor
> versions, and need to track which fields were created or changed in which
> minor versions.
> There other ways that people sometimes deal with the backwards
> compatibility issues, but the question is whether they are applicable to
> UBL.  For example, a comprehensive set of test examples can provided a
> sufficiently good regression test of backwards compatibility, good enough
> to satisfy users.  However, we don't have such a set of test examples
> right now.  I've also worked on a project where the Schemas were generated
>  from a model, and in that case I could trace backwards compatibility, at
> the level that was important to my users, by "compiling" the Schemas into
> Java and checking (by compilation) that each new minor version interface
> was a valid extension of the previous.  However, I don't see this method
> being suitable either.  I just wanted to point out that there are various
> mechanisms one can use to establish backwards compatibility; we need to
> find at least 1 that works for UBL.
> It seems to me that UBL has a good set of design rules for creating new
> major versions of models/Schemas.  However, I do see that there is still a
> lot to do in order to provide the necessary support for minor versions,
> which is something we never had much opportunity to test until we
> (temporarily) started 1.1, and which we won't really have an opportunity
> to get to grips to until we do have to release a 2.1, 3.1, whatever.  My
> experience is that you always learn lessons from doing backwards
> compatible minor versions that you won't have foreseen when doing the
> initial major version.  It's the normal flow of things, but we have to be
> prepared for the idea that it might require some changes to the NDRs as
> they stand now.
> Anyway, I hope this provides some context as to why these issues are
> coming up, and weren't necessarily resolved when the NDRs were done for
> 1.0.  Ultimately, UBL needs to agree on a solution for backwards
> compatible minor versions that (a) satisfy's UBL's needs to have a
> workable process, and (b) provides sufficient confidence to its users that
> minor versions really are backwards compatible.
> Cheers, Tony.
> -- 
> Anthony B. Coates
> London Market Systems Limited
> 33 Throgmorton Street, London, EC2N 2BR, UK
> http://www.londonmarketsystems.com/
> mailto:abcoates@londonmarketsystems.com
> Mobile/Cell: +44 (79) 0543 9026
> [MDDL Editor (Market Data Definition Language), http://www.mddl.org/]
> [FpML Arch WG Member (Financial Products Markup Language),
> http://www.fpml.org/]
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