[jdom-interest] Extending JDOM classes

[Brett McLaughlin]

Simon Harris wrote:
> 
> I don't really need data-binding. I just want access to the data-type
> information. I have no classes to bind to. In fact I don't even no what the
> document represents. All I know for example, is there are two elements name
> "applicant/age" and "document/submissiondate" and I wish to compare the text
> values based on their data-type. Ie. in this case the schema tells me
> (somehow) that they are both dates. Therefore I would convert them to dates
> before perforing the comparison.

OK. But I guess my point is that you are still using that information in
a specific context; the trouble, particularly with XML Schema (which is
also one of its strong points) is that an XML Schema is an XML document.
And an XML document can /look/ like a schema, simply by virtue of the
root element (schema) or the namespace definitions. If we added this
type derivation, where reading a schema results in the ability to use
type-specific methods, we have two big problems:

1) We could be assigning meaning (XML Schema meaning) to a non-schema
document, or an XML Schema that is being used differntly (such as not to
express constraints for an XML document, but to represent, for example,
an indexing system, where the data types represent field types for a
GUI, rather than actual data typing in Java).

2) We add a significant amount of processing to the JDOM API for a
fairly small set of uses. Most users will use XML Schema as they use
DTDs - to validate, and nothing else. Direct access to the schema
grammar in those cases is rarely needed or desired, instead just an "OK,
it conforms", or a list of errors. In this case, we have significantly
complicated the API for a relatively small use-case.

I would not be objectionable to something like org.jdom.schema or
something which is a set of additional JDOM classes that deal with XML
Schema specifically. I wouldn't mind seeing the same thing for DTDs, for
that matter. Eventually, we may want to allow creation and access to
these through JDOM structures that extend or amplify the core. In your
case, something like that makes the most sense - perhaps extending
Element, you would have SchemaElement, SchemaAttribute, etc. These are
actual objects that correspond to the allowed types in an XML Schema and
can easily be used (like the rest of JDOM). So maybe something like:

  SchemaElement constraint = new SchemaElement("elementName",
"dataType");
  constraint.setMinInclusive(0);
  constraint.setMaxOccurs(SchemaElement.UNBOUNDED);

It would be very cool, and could also serve your needs.

Thoughts? I don't have cycles to work on it, but I'd support anyone who
did ;-)

-Brett

> 
> Cheers,
> 
> Simon.
> 
> ----- Original Message -----
> From: "Brett McLaughlin" <brett.mclaughlin at lutris.com>
> To: "Simon Harris" <Haruki_Zaemon at hotmail.com>
> Sent: Monday, August 14, 2000 11:57 AM
> Subject: Re: [jdom-interest] Extending JDOM classes
> 
> >
> >
> > Simon Harris wrote:
> > >
> > > I'm really interested in what data-type the schema says the text should
> be.
> > > I'm building a "rules" engine and I'd like to know if the data-type was
> > > "decimal" or "string", etc. so that I can perform the appropriate
> equals(),
> > > lessThan(), greaterThan(), etc. I haven't found any information anywhere
> on
> > > the 'Net indicating that this information is available via even the DOM
> or
> > > SAX. In simple terms I'm trying to have access to the Element
> definition.
> >
> > You're talking about data binding, something more than simply parsing
> > the content of an XML document. Check out my articles on the subject
> > here:
> >
> > http://www-4.ibm.com/software/developer/library/data-binding1/?dwzone=xml
> > http://www-4.ibm.com/software/developer/library/data-binding2/?dwzone=xml
> >
> > The general case, which JDOM is about, is not really somewhere I see
> > this being needed, or even appropriate - it tries to apply context to a
> > specific XML document (including a schema). A straight API (which JDOM
> > is) shouldn't apply context, as it enforces rules on other users who may
> > not want that same context. However, data binding is by definition the
> > specific context of reading these sorts of rules, so it may serve your
> > needs.
> >
> > -Brett
> >
> > >
> > > Thanks for your help,
> > >
> > > Simon.
> > >
> > > ----- Original Message -----
> > > From: "Jason Hunter" <jhunter at collab.net>
> > > To: "Simon Harris" <Haruki_Zaemon at hotmail.com>
> > > Cc: "JDOM Interest" <jdom-interest at jdom.org>
> > > Sent: Monday, August 14, 2000 10:57 AM
> > > Subject: Re: [jdom-interest] Extending JDOM classes
> > >
> > > > > P.S. Did you noticed my question regarding access to data type
> > > > > information from the schema.
> > > >
> > > > Yes, were you asking for getIntValue() kind of methods, or something
> > > > else?
> > > >
> > > > -jh-
> > > >
> > > _______________________________________________
> > > To control your jdom-interest membership:
> > >
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> >
> > --
> > Brett McLaughlin, Enhydra Strategist
> > Lutris Technologies, Inc.
> > 1200 Pacific Avenue, Suite 300
> > Santa Cruz, CA 95060 USA
> > http://www.lutris.com
> > http://www.enhydra.org
> >

-- 
Brett McLaughlin, Enhydra Strategist
Lutris Technologies, Inc. 
1200 Pacific Avenue, Suite 300 
Santa Cruz, CA 95060 USA 
http://www.lutris.com
http://www.enhydra.org