The other day I had a phone call from Michiel Leenaars of the NLnet Foundation, who is busy gearing up for this week's ODF plugfest in the Hague. Michiel had seen my blog post on ODF validation using pipelines, and was interested in whether I could come up with something quick and dirty for providing forensic information about pairs of ODF documents, so they could be assessed before and after they are used by a tool. This could help users check if anything has been incorrectly added or taken away during a round-trip. Here's what I came up with …

Reaching for XProc

Yes again, I am going to use an XProc pipeline to do the processing. The basic plan of attack is:

1. take two documents
2. generate a “fingerprint” for each of them
3. compare the fingerprints
4. display the result in a meaningful, human-readable form

Fingerprinting XML

For a basic comparison between document I chose simply to compare the elements used, and the number of them. This obviously leaves out quite a bit which might also be compared (attributes, text) etc – but is a useful smoke test about whether major structures have been added or lost during a round-trip.

So the overall pipeline will look like this:

<?xml version="1.0"?>

<pipeline name="get-opc-rels" xmlns="http://www.w3.org/ns/xproc"
xmlns:xo="http://xmlopen.org/odf-fingerprint"
xmlns:mf="urn:oasis:names:tc:opendocument:xmlns:manifest:1.0"
xmlns:cx="http://xmlcalabash.com/ns/extensions">

<import href="extensions.xpl"/>

<!-- the URLs of the ODF documents to be processed -->
<option name="package-a" required="true"/>
<option name="package-b" required="true"/>

<!-- get the first fingerprint ... -->
<xo:make-fingerprint name="finger-a">
<with-option name="package-url" select="$package-a"/>
</xo:make-fingerprint>

<!-- ... and the second ... -->
<xo:make-fingerprint name="finger-b">
<with-option name="package-url" select="$package-b"/>
</xo:make-fingerprint>

<!-- combine them into a single document for input into an XSLT -->
<wrap-sequence wrapper="fingerprint-pair">
<input port="source">
<pipe step="finger-a" port="result"/>
<pipe step="finger-b" port="result"/>
</input>
</wrap-sequence>

<!-- style into an HTML report of differences -->
<xslt name="transform-to-html">
<input port="stylesheet">
<document href="style-diffs.xsl"/>
</input>
</xslt>

</pipeline>

A number of things are of note:

• The ODF packages are interrogated using the JAR URI mechanism I described here
• We’re using a custom step <xo:make-fingerprint>, which takes as its input the URL of an ODF document (“package-url”), and which emits a “fingerprint” as an XML document. Obviously this step is not built into any XProc processor, so we’ll need to write it ourselves
• We using XProc’s wrap-sequence step to combine the two “fingerprint” documents into a single document
• We’ll be relying on an XSLT transform to turn this combined document into a nice report, which will be the end result of the pipeline.

Writing the fingerprinting pipeline

To define our custom pipeline <xo:make-fingerprint> we simply author a new pipeline, and give it the type “xo:make-fingerprint”. This can then be invoked as a step. Here’s what this sub-pipeline looks like:

<pipeline type="xo:make-fingerprint">

<!-- the URL of the ODF file to fingerprint -->
<option name="package-url" required="true"/>

<!-- load its manifest -->
<load>
<with-option name="href" select="concat('jar:',$package-url,'!/META-INF/manifest.xml')"/>
</load>

<!-- visit each entry in the manifest which refs an XML resource -->
<viewport name="handle"
match="mf:file-entry[@mf:media-type='text/xml'
and not(starts-with(@mf:full-path,'META-INF'))]">
<cx:message message="Loading item ..."/>

<!-- load the entry -->
<load name="load-item">
<with-option name="href" select="concat('jar:',$package-url,'!/',/*/@mf:full-path)"/>
</load>

<!-- accumulate everything in a <wrapper> document -->
<wrap-sequence wrapper="wrapper">
<input port="source">
<pipe step="load-item" port="result"/>
</input>
</wrap-sequence>
</viewport>

<!-- transform the accumulated mass into a fingerprint -->
<xslt name="transform-to-fingerprint">
<input port="stylesheet">
<document href="make-fingerprint.xsl"/>
</input>
</xslt>

<!-- label it with the package URL, as an attribute on the root element-->
<add-attribute match="/*" attribute-name="package-url">
<with-option name="attribute-value" select="$package-url"/>
</add-attribute>

</pipeline>

Things to notice here:

• We iterate through the ODF manifest looking for XML documents
• All of the XML in the entire package is retrieved and combined into a single mega-document wrapped in an element named<wrapper>
• We’re relying on an XSLT transform, “make-fingerprint.xsl” to do the heavy lifting and turn our mega-document into meaningful (and smaller) “fingerprint” document
• We add the URL of the ODF document to the fingerprint using XProc’s nifty add-attribute step

The Heavy Lifting: XSLT

The XSLT to boil a document down into a fingerprint can be seen here. What it produces is a summary of the elements used in each of the namespaces the document mentions. This extract gives a flavour of the kind of result it produces:

<namespace name="urn:oasis:names:tc:opendocument:xmlns:manifest:1.0">
<element name="file-entry" count="1"/>
</namespace>
<namespace name="urn:oasis:names:tc:opendocument:xmlns:meta:1.0">
<element name="generator" count="1"/>
</namespace>
<namespace name="urn:oasis:names:tc:opendocument:xmlns:office:1.0">
<element name="automatic-styles" count="1"/> 
<element name="body" count="1"/>
<element name="document-content" count="1"/> 
<element name="document-meta" count="1"/>
<element name="document-styles" count="1"/>
<element name="font-face-decls" count="2"/>
<element name="meta" count="1"/>
<element name="spreadsheet" count="1"/>
<element name="styles" count="1"/>
</namespace>

Returning now to our main pipeline, we can see it makes two calls to (or should that be “sucks on”) the sub-pipeline to generate two fingerprints. These are then wrapped with a wrap-sequence step, and we have all we need to generate the final report. Again, an XSLT transform is used to do a comparison operation and the result is emitted as an HTML document intended for human consumption. An example of what this looks like (comparing the OpenOffice and Google Docs versions of Maya’s wedding planner) can be found here.

Putting it to use

The results of this process need to be interpreted on a case-by-case basis. Just because two applications represent notionally the same document with different XML is not necessarily a fault (though I’d like to know why Maya’s Wedding Planner has 2,000 spreadsheet cells according to Google Docs, and only 51 according to OO.o).

The most useful application of this pipeline is to check for untoward data loss when a document is processed by an application – and I understand this is a particular concern of the Dutch government. With this in mind it is possible to take this pipeline further still, checking attribute differences and even textual differences. Though there comes a point when diff'ing XML that it is best to use a specialist tool such as the excellent DeltaXML (I have no association with this product, except knowing it is well-respected through its use among clients). Many an unsuspecting programmer has come to grief under-estimating the complexities of comparing XML documents.

Online ODF Validation

Michiel also asked whether it would be possible to make the ODF validation pipeline I blogged about previously available as an online service. Coincidentally this was something I was working on anyway, though using Java rather than XML pipelines. The result is now available here. Enjoy …

IBM employee and ODF TC co-chair Rob Weir’s latest blog entry seeks to rebut what he terms a “disinformation campaign being waged against ODF”. The writing is curiously disjointed, and while at first I thought Rob’s famously fluent pen had been constipated by his distaste at having to descend further into the ad hominem gutter, on closer inspection I think it is perhaps a tell of Rob’s discomfort about his own past statements.

In particular, Rob takes issue with a statement that he condemns as “Microsoft FUD […] laundered via intermediaries”:

Now Rob Weir is a great blogger, a much-praised committee chair, and somebody who can, on occasion, fearlessly produce the blunt truth like a rabbit from a hat. For this reason, I know his blog entry, “Toy Soldiers” of July 2008 has enjoyed quite some exposure in standards meetings around the world, most particularly for its assertions about ODF. He wrote:

While the anti-MS line here represents the kind of robust corporate knockabout stuff we might expect, it is Rob’s statement that “no one supports ODF 1.0 today. All of the major vendors have moved on […]” which has particularly resonated for users. A pronouncement on adoption from a committee chair about his own committee’s standard is significant. And naturally, it has deeply concerned some of the National Bodies who have adopted ODF 1.0 (which is ISO/IEC 26300) as a National standard, and who now find they have adopted something which, apparently, “no one supports”.

So, far from being “Microsoft FUD”, the idea that “No one supports ODF 1.0” is in fact Rob Weir’s own statement. And it was taken up and repeated by Andy Updegrove, Groklaw and Boycott Novell, those well-known vehicles of Microsoft’s corporate will.

Today however, this appears to have become an inconvenient truth. The rabbit that was pulled out of the hat in the interest of last summer’s spin, now needs to be put into the boiler. Consequently we find Rob’s blog entry of July 2008 has been silently amended so that it now states:

The pertinent change is to item 1 on this list, which now has a weasel-worded (and tellingly tautological) assertion that might make the unsuspecting reader think that ODF 1.0 was somehow supported by the major vendors. Well, is it? Who is right, the Rob Weir of 2008 or the Rob Weir of 2009? Maybe I’ve missed something, but personally I’m unaware of an upsurge in ODF 1.0 support during the last 11 months. My money is on the former Rob being right here.

Okay, I use OpenOffice.org 1.1.5 (despite its Secunia level 4 advisory) out of a kind of loyalty to ISO/IEC 26300 (ODF 1.0), but I’m often teased about being the only person on the planet who must be doing this, and onlookers wonder what the .swx (etc) files I produce really are.

Blog Etiquette

As a general rule, when making substantive retrospective changes to blog entries, especially controversial blog entries, it is honest dealing to draw attention to this by striking-through removed text and prominently labelling the new text as “updated”. Failing to do this can lead to the suspicion that an attempt to re-write history is underway …

Dew Daisy
Originally uploaded by alexbrn

Really enjoying the capabilities of the AF-S DX NIKKOR 35mm f/1.8G. Thoroughly recommended for all Nikon DX shooters.

All Saints, Churchill

Before dawn things didn't look auspicious in Oxfordshire this morning - it seemed likely to be one of those days which start with a succession of gradually lighter grays. But suddenly, past five o'clock the sun blazed out a lovely yellow. There was mist in the valleys and everything looked resplendent.

I hopped in the car and drove looking for a vantage point, but failed to find one. It was as if one could be in the beauy, but never on top of it. Not for the first time I thought a big step ladder would help to photograph the English countryside, whose hedgrerows are often in just the wrong places. Still, walking round in the early morning with a ladder is likely to look a bit suspicious.

Finally, I stopped in Churchill to photograph the church; and behind, a glimpse of the light in the next valley. Next time I will need to plan better.

Cotswold Dawn

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:

• Dave Pawson's Introduction to XProc
• James Sulak's blog postings on XProc
• A nice tutorial by Roger Costello and James Garriss
• xproc.org as a hub site for further resources
• The XProc specification itself, which is fairly readable.

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 ...

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.

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

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:

[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.

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:

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.

So now we have the document to validate, and the schema to use. We simply need to apply one to the other:

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.

Running It

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:

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]

Conclusions

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.