- From: Ralph R. Swick <swick@w3.org>
- Date: Fri, 12 Nov 1999 10:34:43 -0500
- To: caro@Adobe.COM
- Cc: www-rdf-interest@w3.org
At 10:29 AM 11/10/1999 -0800, Perry A. Caro wrote: http://lists.w3.org/Archives/Public/www-rdf-interest/1999Nov/0019 > How do we decide which one to use (RDFSchema vs. XSchema)? This will certainly depend very much on what your application requirements are. In fact, I suspect a large number of applications to be interested in using *both* languages. The understanding that we reached at the Cambridge meeting was that these two languages are complementary, not mutually exclusive. The XML Schema languages permits expressions of some features of XML documents, the RDF Schema language permits expressions of other features of data models. XML Schema cares more about the form of the expression, RDF Schema (and RDF Model&Syntax) care more about the meaning of the expression. Many of us (in both RDF and XML "camps") hope that it will be possible to use both languages together in a single document. So the current confusion about multiple uses of the term "schema" may then be seen to be a clever bit of foresight. > Are we going to have to live in a world where we have to support both, and > have two sets of processors, two sets of specifications, two sets of user > guides, converters to/from, etc., etc.? The kinds of processing one wants to do on *data*, an in particular graph-structured data, will require some additional APIs beyond what is wanted for tree-structured *documents*. Exactly what those general-purpose APIs are is part of what I hope this Interest Group will eventually propose. If a single D{ocument,ata} Object Model processor can reasonably be understood to support both then we ought to make that happen. But multiple object classes that provide different views on a single data structure is also a bit of technology that we all understand how to work with in our toolset. > my conjecture that the reason RDFSchema > is so underspecified is because of the long shadow cast by the impending > XSchema? confirmed. In fact, we made the very explicit decision to defer most data typing mechanisms within the RDF Schema specification in the hope that RDF Schema writers would be able to use the XML Schema data typing language. The RDF Schema Working Group decided that RDF Schema was useful to a sufficiently large community right away without detailed data typing and that it would be a problem for a much longer period of time if these two specifications wound up with similar but slightly different basic data typing facilities. > RDFSchema lacks some > obviously useful features, like concrete syntax for specifying whether a > value is required or optional, or read-only in a named context, etc. One of the primary goals of RDF was to provide a framework in which communities could create vocabularies without having to wait for some central agency, and to permit independently-developed vocabularies to be freely mixed in a document with minimal confusion. When later we discover that there are mutiple terms for the same concept we add that relationship to our RDF graphs too. Semantics such as "required", "optional", "repeatable", etc. were known to be desired within XML Schema too (since they exist in DTDs) and, as above, the RDF Schema Working Group proposed to defer adding this vocabulary in the interest of promoting easier reuse of XML technology. It is very encouraging to hear on this list that others have indeed found the framework and tiny vocabulary set of RDF Schema 1.0 to be useful, understanding that it can easily grow as we identify common needs not handled elsewhere. -Ralph Swick
Received on Friday, 12 November 1999 10:35:00 UTC