Re: Xerces, schema caching, and namespaces
Ah... What i wrote is for Xerces-J but it seems you are talking about Xerces C++. Don't know what is the behavior of Xerces - C but i don't think it would be different than Xerces-J Neeraj Neeraj Bajaj wrote: > > > Daniel McLean wrote: > >> The Xerces-C++ parser has the capability of caching grammars for >> subsequent reuse. Depending on the complexity of the grammar and the >> instance documents, doing can give a significant performance boost. >> However, the way W3C Schema grammars are cached seems a bit strange >> to me. >> >> All "no-namespace" schemas are considered equivalent: a no-namespace >> schema is stored in the pool of cached grammars using the key "". >> This has ... problematic effects. >> >> >> > I worked on caching long time back.. IIRC this is the default behavior > which can be changed, > You can write your own logic to specify the criteria for caching for > ex. targetNamespace + SchemaLocation etc. > Default behavior of Xerces is to store the grammar using > targetNamespace as key. > You can also have mutiple Grammar Pools having different type of > grammars but > then you have to write logic to set appropriate pool per the instance > document parsed which > may be cumbersome.. You might like to check JAXP 1.3 Schema Validation > Framework > which looks at the caching behavior in entirely different way. > > Neeraj > >  > http://java.sun.com/j2se/1.5.0/docs/api/javax/xml/validation/package-summary.html > >  https://jaxp.dev.java.net > >> Rather than invent a new example, I'll pinch one from the Xerces mailing >> list: >> >> >>> First we parse a document based on schema A with root element A_root. >>> The schema is cached on "". Everything is fine. >>> Then we parse another document based on schema A. The cache finds the >>> schema for "" and validates. Everything is fine. >>> THEN we parse a document based on schema B with root element B_root. >>> The parser looks in the cache, finds the schema for "" (type A) and >>> validates. >>> This of course results in a shitload of errors and a failed parse. >>> >> >> [from >> http://marc.theaimsgroup.com/?l=xerces-c-dev&m=107598912614145&w=2] >> >> To me, this behaviour seems wrong. However, the Xerces folk think that >> it's right: >> >> >>> you shouldn't use schema caching if you have different schemas >>> sharing the same namespace (being this the empty one or not). A >>> namespace URI is a "domain", is like saying "when I am talking about >>> music a record is something that has songs in it; when talking about >>> sports a record is the best performance". You are using two schemas, >>> sharing the same "domain" label: nothing wrong with that, provided >>> that you don't mix them. >>> >> >> [from >> http://marc.theaimsgroup.com/?l=xerces-c-dev&m=107599141217514&w=2] >> >> What's the right answer? >> >> A additional but related question: is Xerces right to cache W3C Schemas >> that _do_ target namespaces based on the target namespace of the >> schemas? >> For that to be correct, the target namespace of the schema must be >> considered to play an equivalent role to a DTD's PUBLIC identifier ... >> which doesn't seem unreasonable, but may not be true. >> >> Daniel >> >> ----------------------------------------------------------------- >> The xml-dev list is sponsored by XML.org <http://www.xml.org>, an >> initiative of OASIS <http://www.oasis-open.org> >> >> The list archives are at http://lists.xml.org/archives/xml-dev/ >> >> To subscribe or unsubscribe from this list use the subscription >> manager: <http://www.oasis-open.org/mlmanage/index.php> >> >> >> > > ----------------------------------------------------------------- > The xml-dev list is sponsored by XML.org <http://www.xml.org>, an > initiative of OASIS <http://www.oasis-open.org> > > The list archives are at http://lists.xml.org/archives/xml-dev/ > > To subscribe or unsubscribe from this list use the subscription > manager: <http://www.oasis-open.org/mlmanage/index.php> >
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