Re: [xml-dev] Mailmen, POST, Intent, and Duck Typing

["Andrew S. Townley" <andrew.townley@bearingpoint.com>]

Warning:  it's late, so this may not completely make sense, but I won't
have much of a chance to get to it tomorrow.

On Tue, 2006-02-28 at 23:58, adasal wrote:
> So, putting this together with 
> 
>         I won't even mention the time canonical schemas were modified
>         in-house
>         by one of our partners to add "missing" field length
>         validation and then
>         the ensuing dismay when we tried to give them new ones that
>         were
>         structurally equivalent (without starting this argument ;),
>         but in which
>         the namespace had been altered slightly, and, of course were
>         again
>         "missing" the field sizes.  Ok, I mentioned it.
> 
> this
>          We use markup over delimited ASCII
>          because we want to put more semantic hints as to the
>         producer's
>          intent.   If we want stronger hints, we go
>          to a language like RDF to provide stronger linking among the
>         signs.
>          If we want to send our intent and ensure
>          it can't be misinterpreted
> 
> are you saying that a possible solution to the problem of evolving
> schemas is  the use of meta data?
> This seems so obvious, and yet, in practice it is not being done
> apart, I suppose, from where it has to be, when the schema repository
> is sufficiently large for people to think seriously about how it is
> handled. In other words, it is not being done in everyday development
> AFAIK. Moreover, in themselves, this is what RDF OWL and other
> semantic languages are, richly self describing, but they seem not to
> be used just for that, whereas I see it as a first step towards more
> ubiquitous use. I'm sure I have missed something (several things) but,
> to be clear, what I mean is the situation where the producer just
> means to describe fields in a document, their type, relationship to
> one another and so on, while the consumer can take this description
> and seperate it from any particular set of data it wraps, that is
> compute on the description independantly from the data it contains. I
> guess, use RDF to do RDF. I think I understand that this is what is
> done. Usually the referant is a resource, for instance the often cited
> example of a song with references to composer, and album art. But I
> mean references to a class "text field" with various attributes. This
> would make schema manipulation and usage operate on a completely
> different footing to how it does within the confines of XML/XML
> Schema.
> Adam

Maybe.  Like most things, it depends on the context.  What I was trying
to illustrate with the example you quoted was that, in this case, the
semantics of the data were things that don't have logical
limits--practical ones, perhaps, but if you specify a person's name as 1
or 100 characters, that just changes the representation, not what it
means.  It's still their name.  Our partners were trying to make their
lives easier when attempting to stuff the content from the document into
a database.  Just because I wouldn't do it that way doesn't mean what
they did is "wrong", it just means you have to deal with the
consequences of your decisions.

The point I was trying to make was that they'd tied the schema into
their application based on generated code, binding the specific use of
the message contents into an object which captured those semantics in
that context.  The fact they changed the schema we gave them is a
slightly different issue, and only tangentially relevant to the main
point--if at all.

I haven't seen their code, so I don't know if their system could deal
with validation against a new schema that followed our versioning policy
anyway (which was the nature of the change to the namespace).  This
particular system also exceeds the 50% rule I was mentioning because
they are dealing with nearly all of the data in the message, so maybe it
really isn't that big of a deal.  The rubber has to meet the road
somewhere, otherwise you'll never get where you're going.

However, back to your text field example.  If you really care about
"text field" vs. the data in the text field and what it represents in
the context of your application, then yeah, you could probably describe
your UI or even other parts of your application using RDF or something
similar.  I don't think it would be that simple, though.  However, I'm
certainly no RDF expert.

It just depends on what you're after.  Perhaps I don't fully understand
what you're saying though, and you mean something different.

ast

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