[higgins-dev] Schema Languages (was Revised Higgins data model goals)

["Jim Sermersheim" <jimse@xxxxxxxxxx>]

>>> Anthony Nadalin <drsecure@xxxxxxxxxx> 4/18/06 10:09 PM >>>

> Not saying different schemas, saying different schema language, as
you indicated that we must have a common schema language

also

> Paul what you are saying is that I can't represent the same data in
different schema languages and this is where I disagree, as we do this
in all the programming languages today.

I'm confused on this thread, so bear with me while I try to tease apart
the meanings of what's being said.

If we have a single data model to represent Contexts and DS's, I assume
we want a single model for the schema that governs instances of that
data. I'm not sure why we're talking about schema languages, or even
what that means, but I do see a need to eventually describe the way in
which an application:

a) discovers schema
b) accesses schema (interrogate and update)
c) uses schema to assist in accessing data (Contexts and DS's along
with their data)

Ideally, one unified model will be used for Contexts, DS's, and schema
elements (where the schema for the schema elements is well-known). For
example, a schema element needs to have attributes/relationships just
like a DS does, just like a Context does. The difference is that when
interrogating a schema element which governs a DS, one would expect to
see certain attributes. The consuming applications would likely have
built-in knowledge of what to expect on that type of schema element.  I
_could_ see the need for meta schema elements which are in turn used to
describe the schema elements themselves. That seems like more of a
formality, but has proven useful in other (similar) areas.

In my mind, I keep drawing an analog to XML and XML schema. Both share
the same (in this case) language (XML), and in XML schema there's only
one way of representing things like choices, sequences, default values,
multiplicity, etc. Otherwise, writing schema parsers would really be
hard.

The term "schema description language" and the notion of allowing
different ones, makes me worry that we're trying to introduce something
(or things) completely different from the Higgins model. I'm hoping that
we're just talking about two completely different things. What sounds
scary to me is having an application discover that ContextA's schema is
presented as a file full of serialized UML, while ContextB's schema is
presented as RDF schema.

Jim