Chasing the Light

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.


Notes on Document Conformance and Portability #4

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 ...

<?xml version="1.0"?>
<pipeline name="validate-odf" xmlns="http://www.w3.org/ns/xproc"
  xmlns:cx="http://xmlcalabash.com/ns/extensions"
  xmlns:mf="urn:oasis:names:tc:opendocument:xmlns:manifest:1.0"
  xmlns:o="urn:oasis:names:tc:opendocument:xmlns:office:1.0">

  <!-- 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 -->
  <import href="extensions.xpl"/>

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 -->
  <cx:unzip file="META-INF/manifest.xml">
    <with-option name="href" select="$package-url"/>
  </cx:unzip>

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 ..."/>
  <validate-with-relax-ng assert-valid="false">    
    <input port="schema">
      <document href="odf-manifest.rng"/>
    </input>
  </validate-with-relax-ng>

[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 -->
  <viewport name="handle"
    match="mf:file-entry[@mf:media-type='text/xml'
    and not(starts-with(@mf:full-path,'META-INF'))]">

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 -->
    <cx:unzip name="get-validation-candidate">
      <with-option name="href" select="$package-url"/>
      <with-option name="file" select="/*/@mf:full-path"/>
    </cx:unzip>

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 -->
    <choose name="get-relax-ng-schema">
      <when test="$force-26300-validation='true' or /*/@o:version='1.0'">
        <cx:message message="Validating with v1.0 schema ..."/>
        <load href="OpenDocument-schema-v1.0.rng"/>
      </when>
      <when test="/*/@o:version='1.2'">
        <cx:message message="Validating with draft v1.2 schema ..."/>
        <load href="OpenDocument-schema-v1.2-cd01-rev05.rng"/>
      </when>
      <otherwise>
        <cx:message message="Validating with v1.1 schema ..."/>        
        <load href="OpenDocument-schema-v1.1.rng"/>        
      </otherwise>
    </choose>
    <identity name="the-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 -->
    <validate-with-relax-ng>
      <input port="schema">
        <pipe step="the-schema" port="result"/>
      </input>
      <input port="source">
        <pipe step="get-validation-candidate" port="result"/>
      </input>
    </validate-with-relax-ng>

  </viewport>
</pipeline>

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:

Producer                   FAIL    PASS
---------------------------------------
Google                      X
KSpread                              X
Symphony                    X
OpenOffice                  ? *
Sun Plugin                  ? *
CleverAge                            X
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]

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.

Notes on Document Conformance and Portability #3

Now that the furore about Microsoft’s implementation of ODF spreadsheet formulas in Office SP2 has died down a little, it is perhaps worth taking a little time to have a calm look at some of the issues involved.

Clearly, this is an area where strong commercial interests are in play, not to mention an element of sometimes irrational zeal from those who consider themselves pro or anti (mostly anti) Microsoft.

One question is whether Microsoft did “The Right Thing” by users in choosing to implement formulas the way they did. This is certainly a fair question and one over which we can expect there to be some argument.

The fact is that Microsoft’s implementation decision means that, on the face of it, they have produced an implementation of ODF which does not interoperate with other available implementations. Thus IBM blogger Rob Weir can produce a simple (possibly simplistic) spreadsheet, “Maya’s Wedding Planner” and used it to illustrate, with helpful red boxes for the slow-witted, that Microsoft’s implementation is a “FAIL” attributable to “malice or incompetence”. For good measure he also takes a side-swipe at Sun for their non-interoperable implementation. In this view, interoperability aligning with IBM’s Symphony implementation is – unsurprisingly – presented as optimal (in fact, you can hear the sales pitch from IBM now: “well, Mr government procurement officer, looks like Sun and MS are not interoperable, you won’t want these other small-fry implementations, and Google’s web-based approach isn’t suitable – so looks like Symphony is the only choice …”)

Microsoft have argued back, of course, most strikingly in Doug Mahugh’s 1 + 2 = 1? blog posting, which appears to present some real problems with basic spreadsheet interoperability among ODF products using undocumented extensions. The MS argument is that practical ODF interoperability is a myth anyway, and so supporting it meaningfully is not possible (in fact, you can hear the sales pitch from MS now: “well, Mr government procurement officer, looks like ODF is dangerously non-interoperable: here, let me show you how IBM and Sun can’t even agree on basic features; but look, we’ve implemented ISO standard formulas, so we alone avoid that – and you can assess whether we’re doing what we claim – looks like MS Office is the only choice …”)

Personally, I think MS have been disappointingly petty in abandoning the “convention” that the other suites more or less use. I accept that these ODF implementations have limited interoperability and are unsafe for any mission-critical data, but for the benefit of the “Maya’s Wedding Planner” type of scenario, where ODF implementations can actually cut it, I think MS should have included this legacy support as an option, even if they did have to qualify that support with warning dialogs about data loss and interoperability issues.

But - vendors are vendors; it is their very purpose to compete in order to maximise their long-term profits. Users don’t always benefit from this. We really shouldn’t be surprised that we have IBM, Sun and Microsoft in disagreement at this point.

What we should be surprised about is how this interoperability fiasco has been allowed to happen within the context of a standard. To borrow Rick Jelliffe’s colourfully reported words, the whole purpose of shoving an international standard up a vendor’s backside it to get them to behave better in the interests of the users. What has gone wrong here is in the nature of the standard itself. ODF offers an extremely weak promise of interoperability, and the omission of a spreadsheet formula specification in ODF 1.1 is merely one of the more glaring facets of this problem. As XML guru James Clark wrote in 2005:

I really hope I'm missing something, because, frankly, I'm speechless. You cannot be serious. You have virtually zero interoperability for spreadsheet documents.

To put this spec out as is would be a bit like putting out the XSLT spec without doing the XPath spec. How useful would that be?

It is essential that in all contexts that allow expressions the spec precisely define the syntax and semantics of the allowed expressions.

These words were prophetic, for now we do indeed face a present zero interoperability reality.

The good news is that work is underway to fix this problem: ODF 1.2 promises, when it eventually appears, to specify formulas using the new OpenFormula specification. When that is published vendors will cease to have an excuse to create non-interoperable implementations, at least in this area.

Is SP2 conformant?

Whether Microsoft’s approach to ODF was the wisest is something over which people may disagree in good faith. Whether their approach conforms to ODF should be a neutral fact we can determine with certainty.

In a follow-up posting to his initial blast, Rob Weir sets out to show that Microsoft’s approach is non-conformant, subsequent to his previous statement that “SP2's implementation of ODF spreadsheets does not, in fact, conform to the requirements of the ODF standard”. After quoting a few selected extracts from the standard, a list is presented showing how various implementations represent a formula:

  • Symphony 1.3: =[.E12]+[.C13]-[.D13]
  • Microsoft/CleverAge 3.0: =[.E12]+[.C13]-[.D13]
  • KSpread 1.6.3: =[.E12]+[.C13]-[.D13]
  • Google Spreadsheets: =[.E12]+[.C13]-[.D13]
  • OpenOffice 3.01: =[.E12]+[.C13]-[.D13]
  • Sun Plugin 3.0: [.E12]+[.C13]-[.D13]
  • Excel 2007 SP2: =E12+C13-D13

Rob writes, “I'll leave it as an exercise to the reader to determine which one of these seven is wrong and does not conform to the ODF 1.1 standard.”

Again, this is clearly aimed at the slow witted. One can imagine even the most hesitant pupil raising their hand, “please Mr Weir, is it Excel 2007 SP2?” Rob however, is too smart to avoid answering the question himself, and anybody who knows anything of ODF will know that, in fact, this is a tricky question.

Accordingly, Dennis Hamilton (ODF TC member and secretary of the ODF Interoperability and Conformance TC) soon chipped in among the blog comments to point out that ODF’s description of formulas is governed by the word “Typically”, rendering it arguably just a guideline. And, as I pointed out in my last post, it is certainly possible to read ODF as a whole as nothing more than a guideline.

(I am glad to be able to report that the word “typically” has been stripped from the draft of ODF 1.2, indicating its existence was problematic.)

Curious readers might like to look for themselves at the (normative) schema for further guidance. Here, we find the formal schema definition for formulas, with a telling comment:

<define name="formula">
  <!-- A formula should start with a namespace prefix, -->
  <!-- but has no restrictions-->
  <data type="string"/>
</define>

Which is yet another confirmation that there are no certain rules about formulas in ODF.

So I believe Rob’s statement that “SP2's implementation of ODF spreadsheets does not, in fact, conform to the requirements of the ODF standard” is mistaken on this point. This might be his personal interpretation of the standard, but it is based on an ingenious reading (argued around the meaning of comma placement, and privileging certain statements over other), and should certainly give no grounds for complacency about the sufficiency of the ODF specification.

As an ODF supporter I am keen to see defects, such as conformance loopholes, fixed in the next published ODF standard. I urge all other true supporters to read the drafts and give feedback to make ODF better for the benefit of everyone, next time around.

Notes on Document Conformance and Portability #1

Richard Gillam’s handy book, Unicode Demystified: A Practical Programmers Guide to the Encoding Standard, contains an example of right-to-left text appearing in a prevailing left-to-right writing direction:

Avram said “מזל טוב.‏” and smiled.

Whether you see here what you are meant to see here will depend on your browser's Unicode support, and whether you have Hebrew fonts installed. Properly rendered, it will look something like this:

In reading order, the first character after “said” is the “מ” character to the left of the closing quotation mark. The text then runs from right to left until the full-stop, and then resumes with “and smiled”. In Unicode, this text is not represented in rendering order, but reading order – it is up to the renderer to make space and reverse direction at the correct points. Here is the text represented as XML in a paragraph in an ODF document (get the document here):

<text:p>Avram said “&#x5de;&#x5d6;&#x5dc; &#x5d8;&#x5d5;&#x5d1;.&#x200f;” and smiled.</text:p>

One of the great things about XML is its solid basis in Unicode and therefore its use of the Universal Character Set (ISO/IEC 10646). XML defines a number of encodings for this character set, and in the XML above the numeric character reference mechanism is used for the Hebrew characters. Notice, just to the left of the full stop the use of U+200F 'RIGHT-TO-LEFT MARK' which specifies that the full stop is part of the right-to-left character sequence.

Viewing this document in three ODF applications (OpenOffice 3, Google Docs with FireFox, and the new MS Office 2007 SP2) give the correct result every time. That is good news.

And if, for an ODF application, the character sequence did not appear correctly (if, say, the full stop was out-of-place) we would be able to say unequivocally that it was faulty; and we would be able to point to the Unicode specification where the correct behaviour was described. We (the user) would be able to bang the table and demand the bug was fixed.

This kind of process is one one of the pillars of conformance testing: application conformance testing, to be exact. Where we have a solid spec and observable behaviour we can compare the two and make a judgement.

Where we don't have a solid spec, things get trickier. For the standardiser's viewpoint, and if its not too highfalutin (and anyway, I claim Cambridge resident's special rights), we might want to quote Wittgenstein on such occasions: "Whereof one cannot speak, thereof one must be silent".