In my last post I wrote about the reaction to Microsoft's ODF support in the recent service pack released for their Office 2007 product, and in particular how claims of its "non-conformance" seemed ill-founded. Now, to look a little deeper at the conformance question, I will use an XML pipeline to validate some would-be ODF documents, to get a clear-sighted and spin-free look at what the state of ODF conformance really is.
XML Pipelines: The Next Big Thing
For many years pipelines have been recognised as something the XML community badly needed. Eager markup geeks would seek out Sean McGrath or Uche Ogbuji to hear miraculous tales of how XML pipelines could be put to work; some bold experimenters would try to coerce technologies like Apache Ant into action, and some pioneers would even specify and implement their own pipelining languages – witness, for example Eric van der Vlist's xvif, or maybe XPL, which happily sits at the heart of the awesome Orbeon Forms framework.
Now however, the W3C is on the cusp of finalising its XProc language and this looks set to bring pipelines into the mainstream. I am convinced that XProc is the most significant specification from the W3C since XSL, and fully expect it to become as pervasive in all XML shops.
So what are pipelines? Well, as we know XML processing models can be described as conforming to the model: "in; out; shake it all about". The "in" bit is catered for by XML storage technologies (eXist maybe), and the "out" bit is catered for by web servers; XProc is for the "shake it all about" bit, where, with XSLT it will become the engine of many an XML process. XSLT is great for transforms but less convenient for a number of day-to-day things we routinely want to do with XML: validating, stripping element, renaming attributes, glomming together, splitting up ... Essentially, pipelines are for doing stuff to XML in a step-by-step way, but without the overhead of a full-on programming language, since XProc pipelines are written using nice, declarative XML.
Pipelines and Office Documents
One of these typical "day to day" tasks is validating XML inside ZIPs. Both ODF and OOXML resources are not simply XML documents, but "packages" (ZIP archives) of content which include several XML documents. So to perform a full validation, we need to visit the XML resources in the package and validate them all against their governing schemas to get an overall validation result. This is exactly the sort of scenario where XML pipelines can help.
A Walk Through
I am going to describe an XML pipeline for performing ODF validation using Calabash, a FOSS (GPL v2) implementation of XProc for the JVM written by Norm Walsh (the XProc WG chair). I'm not going to cover the absolute basics, for those (and more) consult some of the excellent material on XProc already appearing on the web such as:
We start, immediately after the root element, with a couple of "option" elements. These allow values to be passed in from the outside. In our case, we need the name of the package we want to validate ...
<pipeline name="validate-odf" xmlns="http://www.w3.org/ns/xproc"
<!-- the URL of the package to be validated must be supplied by the caller -->
<option name="package-url" required="true"/>
<!-- whether to enforce use of the IEC/ISO 26300 schema -->
<option name="force-26300-validation" select="'false'"/>
Next we import some extensions. Like XSLT, XProc is designed to be extensible and already additional sets of functions are becoming available. Calabash ships with a handy function for ZIP extraction which we are going to need.
<!-- we use the Calabash extension in this library for looking inside ZIP files -->
Now we start the processing proper. This next step uses the ZIP extraction mechanism to pull the "manifest.xml" document out of the archive and outputs that XML for onward processing
<!-- emits the package manifest -->
<with-option name="href" select="$package-url"/>
As a sanity check, we are going to make sure that this manifest actually conforms to the ODF manifest schema. I made this schema by manually extracting it from the ODF 1.1 specification (here referred to as "odf-manifest.rng"). As you can see, XProc makes this kind of document validation a cinch:
<!-- validate the manifest against the manifest schema -->
<cx:message message="Validating manifest ..."/>
[Update: I have added an @assert-valid="false" attribute here, as this is just a 'sanity check']
Now we start to visit the individual documents in the package referenced by the manifest. This is done here using the viewport step, which offers a kind of "keyhole surgery" option allowing us to isolate bits of a document. Here we're interested in all the <file-entry> elements in the manifest which (1) have a media type of "text/xml" and (2) aren't residing in the "META-INF" folder itself.
<!-- visit each file entry in the manifest which targets an XML resource -->
For each of these <file-entry> elements, a @full-path attribute specifies the name of an XML resource in the ZIP, again we use the unzip step to pull each of these XML documents from the archive:
<!-- assume paths are relative to package base, and extract the XML resource -->
<with-option name="href" select="$package-url"/>
<with-option name="file" select="/*/@mf:full-path"/>
Once we've grabbed an XML resource, we need to work out which schema to use to validate it. Generally this can be done by looking at a @version attribute on the root element. However, ODF does not make this mandatory and so implementations are free to omit it. ODF specifies no fall-back rules, so we need to invent our own. What I've done here is to use the version specified, but fall back to the most recent published standard (1.1) when it is not specified.
<!-- emits the schema RELAX NG that corresponds to the ODF version -->
<when test="$force-26300-validation='true' or /*/@o:version='1.0'">
<cx:message message="Validating with v1.0 schema ..."/>
<cx:message message="Validating with draft v1.2 schema ..."/>
<cx:message message="Validating with v1.1 schema ..."/>
So now we have the document to validate, and the schema to use. We simply need to apply one to the other:
<!-- and: validates the candidate against the schema -->
<pipe step="the-schema" port="result"/>
<pipe step="get-validation-candidate" port="result"/>
Et voilà, a complete pipeline for validating ODF instances. Running it against packages which contain invalid XML will cause the pipeline processor to halt and report a dynamic error, for that is the default behaviour of the validate-with-relax-ng step.
Since ODF is clear that invalid XML signals non-conformance to the spec, we know that any package which fails this pipeline is, beyond argument, non-conformant.
Rob Weir helpfully provided a ZIP of the spreadsheets used for his Maya's Wedding Planner piece. Consult his blog entry for details of how these documents were produced. Putting these 7 test files through our pipeline we get this result:
Producer FAIL PASS
OpenOffice ? *
Sun Plugin ? *
MS Office 2007 SP2 X
* See update below
So, Why the Failures?
- Google failed because for some bizarre reason the manifest.xml document in its package specified a document type declaration referring to a non-existent "Manifest.dtd"; the processor cannot find this DTD and aborts with an IO Exception.
Symphony failed because its styles.xml document contained a date-value of "0-00-00". This fails to match the datatyping rules the ODF 1.1 schema uses to police date values.
OpenOffice failed because its manifest was not valid to the 1.1 schema. Now, this is an odd result as the manifest claims to be valid to version "1.2" of the ODF schema, yet consulting the latest drafts of ODF 1.2 it appears the manifest schema is not defined there, but has been planned for being specified in a new "Part 3" of ODF. I cannot find Part 3 of ODF in draft – maybe the OOo code has been written, but the standards text not fitted to it yet. If somebody can point me to a public draft of this schema, I'd like to re-run this test. [Update: I have now been pointed at the draft of Part 3 of ODF 1.2, and it does indeed contain a new schema. This draft is unfinished and contains non conformance clause, so it is not really possible to know for sure whether a package conforms to it. However, the OOo package here is invalid to the schema. I am going to assume that Part 3 will mirror the draft of Part 1 of ODF 1.2, and so will require schema validity. On that (reasonable) basis this OOo package is non-conformant; but of course the draft might change tomorrow. We do not know quite what version of the spec is being targetted here ...]
The Sun Plugin also failed because its manifest uses a @manifest:version attribute which the 1.1 schema does not declare. Again, maybe this is valid to some draft schema I have not seen, but it certainly does not conform to any published version of ODF. As above, if I can get a new schema I can re-run the test. [Update: see bullet above, it's the same here]
There had been a lot of spin in the blogosphere about who is, and who is not, supporting ODF at the moment. This validation test focusses on a small but important area of that discussion: conformance. One of the reasons it is important is that it is testable. From the test above we have the hard fact that most of the mainstream ODF applications are failing to emit standards-conformant ODF, even for a case as simple as "Maya's Wedding Planner". Surprisingly when assessing conformance it appears KOffice, Microsoft and CleverAge are leading the conformance pack; while Sun, Google and IBM have fallen behind.
To me this merely goes to confirm one of the fundamental dynamics of standardisation; done right, standards wrench "ownership" from those who thought they owned them, and distributes that ownership through the community at large. We, as users, should be applauding the widening adoption of ODF - and should be keeping the pressure on those vendors that seem to have been left behind, to raise their games.