RE: RNG vs. XSD : is the use of abstract types and polymorphi
That kind of separation seems logical, particularly in the context of maintaining the ontology separately, whilst the XML Schemas are manually kept in sync with the ontology. Other contexts however do exist: Imagine an UML ontology which is making good use of abstract classes and inheritance. Suitable tools can translate UML and generate the XML library schema components (similar to OASIS UBL's CBC and CAC library schemas). The generated library components mirror the UML inheritance and abstract classes. On the other hand, the actual XML document schemas, which are composed by cherry picking from the XML library components, are not allowed to define new abstract types or new inheritances. Such governed use of inheritance and abstract types is almost invisible when looking at a document schema (good for users), yet provides benefits in component library structure and use. For example, document schemas can include the automatically embedded documentation containing the plain text definition of the UML class attribute, some of which happen to be inherited attributes. Just to add a different perspective. Juerg www.d-m-s.co.nz > -----Original Message----- > From: Costello, Roger L. [mailto:email@example.com] > Sent: Wednesday, 14 March 2012 12:30 a.m. > To: firstname.lastname@example.org > Subject: RE: RNG vs. XSD : is the use of abstract types and > polymorphism a good or bad thing for schemas for XML? > > Hi Folks, > > I have been thinking about the issue of "inheritance" in schema languages for > XML. > > Recall that James Clark says (paraphrasing) that it is not the role of a > schema language to model conceptual or semantic relationships such as > inheritance. Such relationships are best modeled elsewhere. > > That makes sense to me. Separation of concerns is a good thing. Use a schema > language to define a template for syntactic organization. Using my chocolates > example, use a schema language to show the organization of boxes (elements) > and what chocolates (data) goes into each box. > > Use other technologies for expressing relationships and meaning -- use > ontologies, data specifications, UML, etc. > > That's a nice, clean separation of concerns. That yields more productivity and > better results. (Adam Smith, Wealth of Nations) > > I wonder why XML Schemas ever introduced inheritance machinery (derive-by- > extension, derive-by-restriction, element substitution) into the language? > The inheritance machinery muddies things up. It results in XML Schema trying > to be both a language of expressing syntactic template and a poor man's pseudo > UMLish relationship ontology language. > > This muddiness has created enormous confusion over the years. > > "XML Schema is just syntax." > > "No, XML Schema is semantics, just look at the meaning in this inheritance > tree." > > It seems that the prudent path is to avoid all inheritance machinery in XML > Schema. > > Don't use derive-by-extension, derive-by-restriction, and element substitution > . Use XML Schema just for expressing templates of elements and attributes. > > Use ontologies, data specifications, UML, etc. for expressing relationships > and meaning. > > Thoughts? > > /Roger > > _______________________________________________________________________ > > XML-DEV is a publicly archived, unmoderated list hosted by OASIS to support > XML implementation and development. To minimize spam in the archives, you must > subscribe before posting. > > [Un]Subscribe/change address: http://www.oasis-open.org/mlmanage/ > Or unsubscribe: email@example.com > subscribe: firstname.lastname@example.org List archive: > http://lists.xml.org/archives/xml-dev/ > List Guidelines: http://www.oasis-open.org/maillists/guidelines.php
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