[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XML Schemas: lost "open content models"?
Don Park wrote: > My particular dislike for the current crop of schema initiatives > is that all of them seem to target the syntax layer instead of > the information model layer. Current syntax-targeted approaches > decrease extensibility while increasing fragility of XML-based > documents. Also, I find current obsession with document-level > schemas in conflict with the increasing trend toward compound > documents/streams. Micro-schemas which define basic building > blocks are preferable to macro-schemas which define complete > document structure. Then Don should love XML Schemas, since that is exactly its basis. Almost the only thing in it that has document scope is ID/IDREF; and even there it also provides an XSLT-inspired key mechanism. I presume by syntax-related approaches, does Don mean that sequence is bad? XML Schemas operate on the information set not the incoming tokens. It departs from a simple sequence-based grammar approach by: * wildcarding the <any /> particle in content models, to allow various kinds of openness; * providing an <all /> content model type (similar to SGML &) which is position-independent (but note that it is currently only available at the top-level of a content model: some of us feel that anonymous groups are to some extent bad information modeling practise--if a group has semantic significance why shouldnt it be named?); * providing element equivalence classes and abstract elements, allowing you to name the slot in which a required element should go, but defer all type decisions to the schema of the element that will take advantage of it: you can say "some element for credit card number should go here, but I wont provide any type or namespace information for what it will be". This supports frameworks. (I.e., an abstract element is a non-terminal.) Rick Jelliffe *************************************************************************** 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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