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architectural forms and schema type derivation

  • To: xml-dev@l...
  • Subject: architectural forms and schema type derivation
  • From: Bob DuCharme <bobdc@s...>
  • Date: Fri, 18 Oct 2002 10:20:40 -0400

schema architectural
Early explanations of architectural forms[1] often use object-oriented class inheritance as an analogy. You define a structure and some processing (implied or otherwise), and you can then base other structures on that structure. You can call these derived structures anything you want, they can have additional structural components and processing semantics defined, etc. If you want, you can even define structures that are never themselves instantianted, but exist only to provide a basis from which to derive other types.

My question: doesn't W3C schema type derivation provide a way to do this? With my head in two separate places, I was trying to keep up on the architectural forms discussions in xml-dev and reading the architectural forms material in David Megginson's "Structuring XML Documents," and on the other hand working on understanding XrML better, when I realized that XrML's core, which is a series of abstract types defined using W3C Schema syntax, is essentially a definition of architectural forms declared so that others can derive new types from them with their own names and additional structure and processing defined.

Implementing architectural forms this way does make processing dependent on the PSVI, but any implementation will mean reading an instance, reading another document (HyTime: the DTD; Architectural Forms NG: the Architectural Map), and doing some cross-referencing to see if and where the document's elements get mapped. 

Are there any reasons to not consider schema type derivation to be providing the benefits of architectural forms? 

To take this further, we certainly don't want to base a general-purpose linking architecture around W3C Schema, but it makes for a nice exercise: once someone defines an abstract type called SimpleLink, I can derive a Citation type from it, adding attributes such as Disposition, Date, and so forth to define a link meeting a specific purpose because I can assign my own name and additional attributes or subelements to it.

Bob DuCharme          www.snee.com/bob           <bob@  
snee.com>  "The elements be kind to thee, and make thy
spirits all of comfort!" Anthony and Cleopatra, III ii
(bobdc e-mail address used only for mailing lists)

[1] e.g. pg. 81 "Making Hypermedia Work" DeRose and Durand. The Hytime spec iteself at http://www.ornl.gov/sgml/wg8/docs/n1920/html/clause-A.3.5.html#clause-A.3.5.1 says "In object-oriented programming terms, an application-defined derived class (the element type) inherits the properties of its base class (the architectural form)."


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