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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: building an object model of a XML schema
 If I look at XML Schema, I see type definitions that are largely translatable to a sizeable chunk of program code. But XML Schema is, after all, designed around a specific physical representation, so one has to agree with Ron's assertion that object model generation from XML Schema has some problems. On the other hand, object model to XML Schema generation has problems, also, not the least of which is that many of the constraints defined in the object model are operationally based, which doesn't lend them to expression in XML Schema form (the number of ways to express certain data constraints in an object model are literally infinite, as any Obfuscated C contest will attest; not so infinite in XML Schema, however). On the other hand, XML Schema is darn close, probably due more to its SOX roots than intentional design. Tantalizingly close. My UML knowledge is rusty, but I would think it's overkill for data models. What would I, long-term writer of that crufty stuff that goes between application and database or application and XML document, need to make my life easier? Well, darn it, I want a data model (just data, thank you) that I can express as a physical model through some tranformation, and as a set of objects through another transformation. For the general class of data models, I would expect the problem to be hard. For hierarchical data models only, I think the problem is much easier, but not simple. One thing is that I'm missing, in a conceptual data model, the necessary information to build an optimal physical model. I may want a set of elements, for example, to be stored in a hash map, keyed by some attribute value. But hashmaps imply methods, not something for a data model. Hmmm... You could take the approach of JAXB, and create an object binding schema in addition to the data schema. You could take Castor's approach, which is (if I remember) a property list with binding information. Or maybe one could come up with a data model with types rich enough to serve both masters. A hash map is, after all, a type that is universally understood, it's just not a datatype, because it needs methods to work. Maybe it could be called an archetype. Are there enough conceptual archetypes that would provide enough information to allow generation of efficient object model representations? I would think so, STL and classes.zip has a bunch identified. The problem then becomes: can I easily map datatypes to archetypes? If so, I can then build a upon whatever object code is generated by the conceptual model, and the constraints will be identical to those in my data model. Ouch. Now I have a headache... -- Jeff 
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