[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: parser for xml-data?
> -----Original Message----- > From: rbourret@d... > [mailto:rbourret@d...] > Sent: Tuesday, May 19, 1998 1:34 AM > To: xml-dev@i...; Charles Frankston > Subject: RE: parser for xml-data? > 1) How do you use multiple namespaces in a valid document? > That is, if you have > two separate DTDs (schemas), neither of which references > elements in the other, > how do you build a single valid document with both of them? > Elements from the > first DTD can't nest inside elements from the second DTD > (because they aren't in > the second DTD's grammar) and vice versa. The example in > section 3.1 of the > namespaces spec is well-formed, but the spec doesn't explain > how it can be > valid. Presumably, it doesn't match any of the DTDs > presented as namespaces. DTDs are not well-equipped to handle namespaces. It can technically be done: for example, you could allow your outer DTD to have 'ANY' content. XML-Data schemas are designed to integrate with namespaces: <!-- Schema for xyz namespace --> <elementType id="a"> <string/> </elementType> <!-- Schema for zyx namespace (in a separate file) --> <?xml:namespace ns="xyz" prefix="x"?> <elementType id="b"> <element type="x:a"> </elementType> <!-- Instance file --> <?xml:namespace ns="zyx" prefix="z"?> <?xml:namespace ns="xyz" prefix="x"?> <z:b> <x:a/> </z:b> > > 2) The src attribute in your namespace declaration does not > point to a DTD; it > points to an XML-Data file. While the namespace spec does > not prohibit this, I > had simply assumed that the schema would be a DTD. It would > be nice if the > namespace spec clarified that it does not impose any rules on > the format of a > namespace schema. This is important for validating parsers, > as it means that > namespace declarations are dependent on the parser's ability > to read the > particular schema format that is used. (And if a parser can > read multiple > schema formats, how does it know which one to use?) > Most of the XML-Data spec describes the rules of the XML-Data schema file. The schema happens to use XML instance syntax, rather than the separate grammar approach of DTDs. We think this is a big advantage -- you can use all the tools you have for editing XML instance data to edit XML-Data schemas. > 3) Why is production [1] in the namespace spec: > > [1] NamespacePI ::= '<?xml:namespace' (S (PrefixDef | NSDef > | SrcDef))+ '?>' > > instead of: > > [1] NamespacePI ::= '<?xml:namespace' S PrefixDef S NSDef > (S SrcDef)? '?>' > > Is the ambiguity of the production, which needs to be > qualified with the > Required Parts constraint, worth the flexibility in the order > of PrefixDef, > NSDef, and SrcDef? My opinion is no. The ns, prefix, and src parameters to a namespace PI look a lot like attributes (although they are not in a formal sense). Since attributes in XML do not have to be in a particular order, it would certainly be surprising for people to discover that attributes in a namespace have to be a particular order. You're suggesting that the syntax be made harder to use in order to make the productions easier to author. I think this is a bad tradeoff. xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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