[jbosstools-dev] Fwd: Re: [wtp-dev] Question on XML Validation and oracle xsds

Rob Stryker rstryker at redhat.com
Tue Mar 1 21:13:58 EST 2016 

There have been three responses on wtp-dev about my xml schema 
question.   They seem to indicate the problem is with the xml spec in 
general and the different behaviors in various libraries like xerces.

Either way, this thread seems to indicate Jesper and Keith Chong are the 
guys to ping when we have further questions.

- Rob


-------- Forwarded Message --------
Subject: 	Re: [wtp-dev] Question on XML Validation and oracle xsds
Date: 	Thu, 25 Feb 2016 23:43:07 +0100
From: 	Jesper Steen Møller <jesper at selskabet.org>
Reply-To: 	General discussion of project-wide or architectural issues. 
<wtp-dev at eclipse.org>
To: 	General discussion of project-wide or architectural issues. 
<wtp-dev at eclipse.org>



Hi Keith and Rob
(You probably know all this already, but I’ll just add what I know)

I touched some of the validator code a few years back: The number of URI 
resolver interfaces is horrible - one from Platform, one from Xerces and 
one from WTP as I recall), each introducing a slight impedance mismatch.

Really, the XML Schema spec is at fault, by being so vague on the 
semantics of namespaces and schema locations, so Xerces can get away 
with their import policies (first import per namespace wins). So, the 
order of imports matter, and this affects the effective scope of each 
import:

Imagine this scenario where you have to “end-user” schemas A.xsd and 
B.xsd. A relies on namespace C and D, B only on C.
A.xsd imports A_C.xsd, which in turn also imports A_D.xsd (say, they 
were meant to be used together), and all is great, you can validate 
A.xsd by itself — no errors.
B.xsd import a different file B_C.xsd, which doesn’t contain an import 
for namespace D, but and doesn’t need to. B.xsd also validates by itself.
Now we make E.xsd which import A.xsd and B.xsd and uses namespaces 
A,B,C, and D. This should be just fine, and E.xsd can validate on its 
own. The import of B_C.xsd from B.xsd is ignored.
Now flip the imports of A.xsd and B.xsd. This will cause the namespace 
for C to be imported from B_C.xsd, and E.xsd will no longer validate, 
since it never sees the import of A_D.xsd from A_C.xsd. Wonderful, 
isn’t it?
Now, some short-sighted people even practice splitting namespace 
contents up into separate files, for greater “composability”, but 
the major stacks don’t support that.

In Eclipse, the XML Catalog support was supposed to be able to alleviate 
this, by allowing the end users manage the schemas themselves (I’d 
rather not have my IDE be dependent on some external server, even if we 
cache the result). Also, there is an extension point available for 
providing schemas (based on namespace OR schema location IIRC) along 
with plug-ins.

We might be able to improve the error handling and logging side of 
things, but only by tying deeper into the Xerces code.

-Jesper

> On 25. feb. 2016, at 19.01, Keith Chong <kchong at ca.ibm.com 
> <mailto:kchong at ca.ibm.com>> wrote:
>
> Hi Rob
>
> The XML Schema validator is based on the Xerces validator (parser), so 
> I had a discussion with one of the developers. I'll try to answer your 
> questions:
>
> 1) The validator resolves components via imports so if the import is 
> missing, the schema is invalid. See: 
> https://www.w3.org/TR/xmlschema-1/#src-resolve
>
> 2) This is a good question. I suspect that this client schema on its 
> own is 'invalid' and is never intended to be used that way. (There are 
> no global elements too so you can't create an instance document from 
> it). The EE 5 schema includes this schema, so it is valid as part of 
> 'the whole'. eg. If you remove the include directive from the EE5 
> schema, then the EE5 schema is invalid.
>
> 3,4,5) are somewhat related. I'm looking into this.
>
> Regards,
> Keith Chong
> WTP Web Services
>
>
> <graycol.gif>Rob Stryker ---02/16/2016 12:58:33 PM---Hi All: So after 
> running into validation issues for our users' xml files using
>
> From: Rob Stryker <rob.stryker at redhat.com <mailto:rob.stryker at redhat.com>>
> To: "General discussion of project-wide or architectural issues." 
> <wtp-dev at eclipse.org <mailto:wtp-dev at eclipse.org>>
> Date: 02/16/2016 12:58 PM
> Subject: [wtp-dev] Question on XML Validation and oracle xsds
> Sent by: wtp-dev-bounces at eclipse.org <mailto:wtp-dev-bounces at eclipse.org>
>
> ------------------------------------------------------------------------
>
>
>
> Hi All:
>
> So after running into validation issues for our users' xml files using
> our schema for week after week, I finally decided to dig in a little and
> see how the JEE distribution handles validation of schema without so
> many upstream dependencies. It's clear that if a parent or referenced
> schema is invalid, the user will experience obscure validation errors
> when developing their own webapps etc.
>
> With that in mind I opened
> https://bugs.eclipse.org/bugs/show_bug.cgi?id=487851
>
> The usecase is that I simply took oracle's
> javaee_web_services_client_1_2.xsd from
> http://www.oracle.com/webfolder/technetwork/jsc/xml/ns/javaee/javaee_web_services_client_1_2.xsd
> and tried to put it in a dynamic web project and let the validator work
> its magic.
>
> I wouldn't be posting here if it succeeded ;)
>
> The questions are basically:
>
>    1) Why are oracle's xsd's failing to validate? Are they really all
> invalid?
>
>    2) Why has nobody in the world asked Oracle to fix them?
>
>    3) How do we/you, as consumers / extenders of wtp, prevent errors in
> oracle's (or other upstream) xsd's from cascading down to our respective
> jee / appserver-specific schema when our schema import, extend, or
> reference upstream failing xsds?
>
>    4) Is this an error in source-editing plugins for not mapping
> directly to the most commonly used jee namespaces? Would that even fix
> the issue? (It didn't when I tried it but maybe I was doing it wrong).
>
>    5) If oracle won't fix their incomplete xsd's, is it reasonable for
> source-editing to do it, to make sure each and every one validate
> correctly, and that, by extension, all other schema that reference,
> import, or otherwise make use of oracles' schema won't be hit by a
> series of cascading validation errors?
>
> I suppose it's possible our product is simply "doing it wrong", but the
> fact that simply placing an official javaee oracle xsd into a clean JEE
> Mars eclipse environment fails validation is indicative to me that
> something bigger is going on here.
>
> - Rob Stryker
> JBoss Tools And Other Cool Stuff
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