I think there's a better way which I'll sketch (because my project
uses a version of Xerces that is from before the DOM Level 3
interfaces were included, so does something similar using older
stuff).
A standard XML parser may be associated with an EntityResolver, which
supports a method taking a URI and returning an InputSource from which
the content may be read. Similarly, when a reference to a schema
namespace is found in a document (instance or schema) being read by a
validating parser, some kind of resolver will be called, if one has
been attached to the parser, to find the definition of the schema for
that namespace. The namespace URI is the argument to the relevant
method. This resolver thing (might be called LSResolver in the DOM
Level 3 L&S) is an interface, and your implementation may do whatever
it wants. Thus, you could create the resolver with some root location
in the file system as argument, or you could use
ClassLoader.getSystemResourceAsStream() or you could put the schemas
in a database and retrieve their text from there. Your resolver could
consult any schema locations it accumulated during its lifetime if you
had a way to capture these, and wouldn't have to use them literally,
but could interpret them as it wished.
I suggest you consult the Xerces docs about how to install a resolver
for schemas.
Jeff
On 10/8/07, Chris Bray <[EMAIL PROTECTED]> wrote:
> Michael, I'm using Xerces-J 2.9.1, I even upgraded from 2.9.0 today to
> test any changes!
>
> Jeff, can you bear with me here I think I understand you...
>
> Jeff Greif wrote:
> > Maybe an example will be clearer.
> >
> > The instance document is, relative to some subtree of the file system, in
> >
> > instances/articles/doc1.xml
> >
> > There is a set of schemas that apply in
> >
> > schemas/{a,b,c,d}.xsd
> >
> > Suppose a.xsd imports b.xsd, and in addition, doc1.xml refers to
> > components from nsa, the namespace of a, and nsb, the namespace of b.
> >
> > So there are schema locations of the form {nsa, ../../schemas/a.xsd
> > nsb ../../schemas/b.xsd, ... }
> >
> > Now when the reference from doc1 -> nsb is found, the schema locations
> > can be used to find b.xsd.
>
> I'm with you up to here, because the schema locations were defined in
> doc1.xml they are relative to doc1.xml and therefore point to the
> correct xsd files.
>
> > If the reference from a.xsd -> nsb is
> > found, the schema locations will not work, because the location is
> > incorrect relative to the location of a.xsd.
>
> My reference from a.xsd -> nsb is in the form
> <xsd:import namepsace="nsb" schemaLocation="./b.xsd" />
> This path to b.xsd is correct with respect to the a.xsd it is defined in
> (although incorrect with respect to doc1.xml).
>
> However this schema location hint is second in the queue behind the one
> specified in doc1.xml, when Xerces tries to use the one specified in
> doc1.xml here it fails with File Not Found(because when relative to
> a.xsd the doc1.xml's schema location is not valid), reports the error
> and stops parsing so the schema location specified here is never used.
>
> Other parsers continue looking at the hints in schema location and find
> the correct one specified on the <xsd:import> line, is there any way of
> telling Xerces to try all hints matching that namespace (in the same way
> XMLSpy, Microsoft .NET's System.Xml and Saxonica seem to do) rather than
> stop on the first "not found"?
>
> > You couldn't solve the
> > problem by changing the schema locations to look like {nsa,
> > ../../schemas/a.xsd nsb ./b.xsd, ... } because the doc1 -> nsb
> > reference would fail. However, in the first case, if the parser is
> > caching grammars, and the reference from doc1 -> nsb has already been
> > processed, the a.xsd -> nsb reference might not be a validation error
> > -- the schema locations are only a hint to the parser, and if it has
> > located and parsed the right grammar already, it can use it.
>
> So changing the schemaLocation works in my case because in processing
> a.xsd the parser finds b.xsd (via the schemaLocation relative to a.xsd)
> and caches it, therefore meaning it can use the cached copy in doc1.xml.
>
> > These are the problems with using relative URLs for the schema
> > locations, except in certain special cases. For example, if the
> > instance doc is
> >
> > instances/doc1.xml
> >
> > and the schemas are in
> >
> > schemas/{a,b,c,...}.xsd
> >
> > Then these schema locations: {nsa ../schemas/a.xsd nsb
> > ../schemas/b.xsd ...} will work successfully, but only because the
> > paths work whether the reference is from the instance doc or a schema
> > doc.
>
> Ideally I'd like to specify a "try all schema locations before error" or
> "do not stop on file not found error" property since there will *always*
> be one that works when used relative to the current location, is there a
> way of doing this?
>
> I'm guessing there is no "schema locations per file" property to turn
> off the global cache of schema location and switch to a per-file cache?
> Thus forcing Xerces to use the hint found at the current location.
>
> Maybe the easiest way to solve my problem is to re-jig my document
> locations so that the same relative path can be used to locate each of
> the schemas? Not ideal mind since I've spent a long time developing the
> inter-schema links to ensure they can always be linked together and I'd
> like to use that investment in some way and I can't help but think that
> moving the files so the relative paths fit for both scenarios is more of
> a by-product than something implemented by design.
>
> I'm under some commercial pressure here to switch to the method that
> works with the system that the customers use (XMLSpy et al) but I'd
> really like the same examples to work in Xerces-J, we've been extolling
> the virtues of XML and XMLSchema as the "common language" to unify our
> industry's data exchange and it'd look bad to have to change the
> examples we are producing to make them work in different parsers!
>
> Once again, that ended up a lot longer than I expected and I hope it
> makes sense, thanks for your time and patience.
> Chris
>
> > Jeff
> >
> >
> >
> > On 10/8/07, Chris Bray <[EMAIL PROTECTED]> wrote:
> >> Jeff.
> >>
> >> My comments inline.
> >>
> >> Chris
> >>
> >> Jeff Greif wrote:
> >>> When a relative URL is used for the location of an imported schema, it
> >>> is supposed to be relative to the URL of the importing document. So
> >>> if your instance document directly references the namespaces of one or
> >>> more schemas for validation, whose URLs are interpreted relative to
> >>> the location of the instance document. Probably some of the schemas
> >>>
> >> So my instance document _should_ have relative paths to the individual
> >> schemas in it's schemaLocation?
> >> Does the fact that Xerces is "changing" the base path to that of the
> >> first specified schema for each subsequent schema constitute a bug?
> >> Should I log this somewhere more formal?
> >>> contain <xsd:import> elements; those would require URLs relative to
> >>> the schema importing them.
> >>>
> >> Each of those schemas then further includes others using <xsd:import>
> >> and <xsd:include> (for example core.xsd actually includes about 30 or 40
> >> smaller schemas from ./Core/schemaname.xsd) and this works as I'd
> >> expected it to.
> >>> Some of the schemas might be referenced both in the instance document
> >>> and in imports from other schemas referenced in the instance document.
> >>> I'm not sure there's a specification of where they must be found if
> >>> relative URLs are used. This may depend on the ordering of processing
> >>> of those references by the parser/validator.
> >>>
> >> When that is the case I am 100% sure that both the instance document and
> >> the "sub schemas" refer to the exact same document, so it shouldn't
> >> matter which of the references Xerces is using, it will resolve to the
> >> same schema anyway.
> >>> There is a section in the XML Schema 1.0 spec addressing this issue.
> >>>
> >>> Jeff
> >>>
> >>>
> >>>
> >>> On 10/8/07, Chris Bray <[EMAIL PROTECTED]> wrote:
> >>>
> >>>> Parshant,
> >>>>
> >>>> Changing the working dir of the JVM doesn't seem to make any difference,
> >>>> using dom.Counter from the Xerces-J samples the parser still seems to
> >>>> change the working dir first to wherever the xml file is located, then
> >>>> to wherever the first xsd file specified is located and need all
> >>>> subsequent locations to be relative to that.
> >>>>
> >>>> Absolute paths work fine but I'm trying to include these files bundled
> >>>> in with a set of schema as examples of how to use the format, hence I
> >>>> don't know where my users will unzip the archives to (C:\Users\username,
> >>>> c:\projects\projectname\, /usr/local/projects, /home etc) so I can't set
> >>>> absolute paths in my distributed files.
> >>>>
> >>>> I was hoping to not need to actually write my own parsing program, just
> >>>> use the output from dom.Counter and a schemaLocation hint (which fits my
> >>>> needs perfectly) since I'm not really a Java developer.
> >>>>
> >>>> I saw that jEdit page but I'd rather make my schemas validate against a
> >>>> standard Xerces installation than modify my jEdit installation to make
> >>>> them work, I feel this would be more useful for my users.
> >>>>
> >>>> Chris
> >>>>
> >>>>
> >>>> Prashant Reddy wrote:
> >>>>
> >>>>> I think the relative paths you have specified in the schemaLocation will
> >>>>> be resolved against the "working dir". The working dir is usually the
> >>>>> directory at the cmd prompt when you launched the JVM.
> >>>>>
> >>>>> Have you tried giving absolute path to the XSD files ?
> >>>>>
> >>>>> A more portable solution to finding schema files locally is to use
> >>>>> EntityResolver[1].
> >>>>>
> >>>>> If you are using JAXP 1.3/ JDK 1.5+ see :
> >>>>> https://jaxp.dev.java.net/article/jaxp-1_3-article.html
> >>>>>
> >>>>>
> >>>>> [1]:http://java.sun.com/j2se/1.5.0/docs/api/org/xml/sax/EntityResolver.html
> >>>>>
> >>>>> Hope this helps.
> >>>>> -Prashant
> >>>>>
> >>>>>
> >>>>> On Mon, 2007-10-08 at 13:17 +0100, Chris Bray wrote:
> >>>>>
> >>>>>
> >>>>>> All.
> >>>>>>
> >>>>>> Please go easy on me as I'm a newbie here, if this is a really obvious
> >>>>>> problem I'm really sorry!
> >>>>>> I've been using Xerces to validate XML for a while now, and I've found
> >>>>>> a
> >>>>>> troublesome scenario.
> >>>>>>
> >>>>>> In the top of my xml files I have a line specifying the location of the
> >>>>>> external schemas required for this xml file like so:
> >>>>>>
> >>>>>> xsi:schemaLocation="http://www.diggsml.org/0.9.2
> >>>>>> ../Schemas/diggs/core.xsd http://www.diggsml.org/0.9.2/geotechnical
> >>>>>> ../Schemas/diggs/geotechnical.xsd "
> >>>>>>
> >>>>>> In this case specifying two namespaces and their associated schema
> >>>>>> files
> >>>>>> (files exist and paths are correct).
> >>>>>>
> >>>>>> However this doesn't work using Xerces. I am required to change my
> >>>>>> schemaLocation attribute so that the first path points to its xsd, then
> >>>>>> subsequent entries are relative to that first xsd, not to the current
> >>>>>> file, like so:
> >>>>>>
> >>>>>> xsi:schemaLocation=" http://www.diggsml.org/0.9.2
> >>>>>> ../Schemas/diggs/core.xsd http://www.diggsml.org/0.9.2/geotechnical
> >>>>>> ../geotechnical.xsd "
> >>>>>>
> >>>>>> Is there any way I can change this to work like the first example, as
> >>>>>> other parsers (XMLSpy and Stylus Studio in particular) require the
> >>>>>> first
> >>>>>> syntax, all paths relative to current doc, what I believe to be correct
> >>>>>> behaviour. I don't know how to build Xerces-J from source to fix(?)
> >>>>>> this
> >>>>>> myself but I'd be willing to try if anyone can help me get it building.
> >>>>>>
> >>>>>> Since my customers are all using XMLSpy etc I'm having to produce my
> >>>>>> example files in the earlier syntax, stopping my from using Xerces to
> >>>>>> validate them.
> >>>>>>
> >>>>>> As the biggest advocate of Free/OpenSource software in our group (jEdit
> >>>>>> with Xerces plugin in particular) I really don't want to have to change
> >>>>>> to use XMLSpy or Stylus Studio but this is quite awkward for me!
> >>>>>>
> >>>>>> That ended up being a longer mail than I'd expected! I hope you can
> >>>>>> help, if there's any more information you need (or a small set of
> >>>>>> sample
> >>>>>> files) let me know.
> >>>>>>
> >>>>>>
> >>>>>> Chris Bray
> >>>>>> Software Engineer (DIGGS Project)
> >>>>>> Keynetix Ltd.
>
>
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