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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Schema concepts
 > Well, a **processor** must have methods for the elements it's processing. > But another processor (or stylesheet) might have very different ones. > Example: using a rdbms I create a new view joining three tables. I can do > this on the fly, even the view can be temporary. This action was not a > method of any one table, nor of the view instance (even though I > can imagine > a class called a viewFactory that would create the view) nor even of the > schema. I've spent most my career writing code mapping relational schemas (and, lately, XML-Schemas) to application-specific class structures and let me tell ya-- it ain't a lot of fun. True, it's a living, but I really stand to make more money shipping product rather than writing it. For database applications, there are scads of tools out there that help, but it seems none of them work quite right or quite well enough. I think that's due in part to the chasm that separates relational schemas from hierarchical ones. Both SQL and OOP languages have strong theoretical foundations, they're both 'complete', and you can make them work together... just not very easily. Not to mention that if you talk 'database' to most programmers, you tend to get glazed looks. The two worlds have different mindsets and ways of thinking about data. So now comes along this new hierarchical data structure, called XML, which more easily maps to OOP classes than relational tables do. All we need is some schema to enforce data integrity, and all this data flying around from app to app has some chance of being correct. Is XML-Schema that schema? Yes, it's complete, and it's been developed by some very bright people with strong formal background. They're proud of what they've written, and they should be: it's a technically impressive piece of work. But it's not simply OOP-like: it has two hierarchies (one for types, one for data elements), two types of derivation, semantic linkage via 'equivClass', something called ContentModel (why?), user-defined datatypes, and some doodad called a 'facet' (which I can grok for all of about five minutes at a stretch). There's various sundry other structures, but I'd have to spend 15 minutes skimming through the current spec to remember what they all are. Now, somebody is going to try to make a tool that maps XML-Schemas to class definitions of my favorite OOP language of the moment. How easy is it going to be for them? How much of the complexity I don't use or want or care about can they hide away from me? Will the mapping be so complex and so garbled that all tools from all vendors will essentially be useful for not much more that prototypes of real applications? AND HOW MUCH WILL THEY COST?? I'm the first to admit I'm not a true tech-head; there are plenty of people who are who will make a lot of money achieving gurudom in the field of XML-Schemas. I wish them well. What I want is something that will help me get some already-late application out the door using technology that has a chance of being relevant five years from now. If that technology gets in the way of that goal because it's so complex I have to spend half my time reading about it (obfuscated XML-Schema contests anyone?), then I'm not being as productive as I could be. Don't get me wrong-- I'm not angry, I'm not hysterical. It's just that I've seen a lot of projects fail because they worried too much about being optimally efficient or fully featured or technically sexy and not enough about simply getting the product out in the simplest way possible. Such, I fear, is XML-Schema. *************************************************************************** This is xml-dev, the mailing list for XML developers. To unsubscribe, mailto:majordomo@x...&BODY=unsubscribe%20xml-dev List archives are available at http://xml.org/archives/xml-dev/threads.html *************************************************************************** 
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