July 14, 2005

Microsoft Certification: MCP Program Takes New Road in September

Microsoft refreshes their professional certifications program: Changes are afoot in the Microsoft Certification Program that can be labeled as "evolutionary"; that is, changes to the certification process will be implemented over time, as newer technologies become generally available. According to Valvano, Microsoft will follow tradition, releasing exams for SQL Server ...

Expert Panel Podcast: SQL/XML, XQuery and Databases

Ken North: WebServicesSummit.com has released two podcasts of a panel discussion with Ron Bourret, Dana Florescu, Michael Kay, Jonathan Robie and Michael Rys. The discussion topics include XQuery, native XML databases, SQL/XML databases, XSLT and related topics. The part 1 podcast (MP3 audio) focuses primarily on XQuery (running time: 34:03 ...

July 12, 2005

Outputting HTML with XslCompiledTransform and XmlResolver

I was wrong in my last post. Here is how one can output HTML with XslCompiledTransform when XmlResolver needs to be passed to Transform() method. using (XmlReader src = XmlReader.Create("../../source.xml")) { XslCompiledTransform xslt = new XslCompiledTransform(); xslt.Load("../../style.xslt"); XmlWriter result = XmlWriter.Create(Console.Out, xslt.OutputSettings); xslt.Transform(src, null, result, new XmlUrlResolver()); } The key ...

So my the only left complaint about XslCompiledTransform's API is the lack of Transform(IXpathNavigable, XsltArgList, XmlWriter, XmlResolver) method. That means that if by any bad chance you happen to be transforming already loaded XmlDocument or XPathDocument and need to provide XmlResolver - you can't. You will need to pass XmlReader over your XmlDocument or XPathDocument (using XPathNavigator.ReadSubTree() method) and then XslCompiledTransform will load passed XmlReader into another XPathDocument! So your source XML in memory will be duplicated with no reason.

July 11, 2005

XslCompiledTransform API bug (update - not a bug, my fault)

I'm porting nxslt utility to .NET 2.0 with XslCompiledTransform as XSLT processor and I just found out XslCompiledTransform API is really severe broken. I was writing before that the only Transform() method overload that accepts XmlResolver outputs to XmlWriter. So if you want to create HTML and to have some ...

As Anton Lapounov pointed out XmlWriter is .NET 2.0 is actually capable to write not only XML, but also HTML or text. This behavior is controlled by XmlWriterSettings.OutputMethod property. But this property appears to be read-only (setter is internal). And after all this doesn't really solve my problem with nxslt utility porting, because in a general purpose XSLT utility XSLT output method should be controlled by a XSLT stylesheet, not by code that run transformation.

Update: I was wrong here. It can be done just fine with no any hacks, I just didn't get the way it's meant to be done. See more at the next post.

July 10, 2005

Loading XPathDocument with XmlWriter

What I dislike in System.Xml v2.0 (and v1.X for that matter) is a poor support for push-based XML processing. Somehow it's all about pull - XmlReader, while push - XmlWriter seems to be a second class citizen. For instance one can't populate XML into XPathDocument or XSLT stylesheet into XslCompiledTransform ...

As a matter of fact, XSLT chaining problem can be solved using XmlDocument, but alas it's still huge, slow and overkill for scenarios where read-only XML store is required.

Apparently this unfortunate state of the art has something to do with SAX vs XmlReader battles in early .NET days, which XmlReader definitely won. In .NET 1.X there wasn't even a standard way to write to XmlDocument using XmlWriter! Happily Chris Lovett came to the rescue with XmlNodeWriter.

An ultimate solution for the XML pipelining problem in .NET would be XmlWriterReader - a component that bridges XmlWriter and XmlReader. It can be implemented either by efficiently caching internally the whole stream of XmlWriter events and reading them after or by two-threaded synchronized XmlWriter/XmlReader. The good news is that it can be said for sure that soon such component will be implemented for the Mvp.Xml library. Stay tuned.

Still I wonder why all these hurdles. Let's take XPathDocument class. XSLT chaining problem could be solved be XPathDocument loadable from a XmlWriter. It's not. It accepts URI, Stream, TextWriter or XmlReader. But if you look inside XPathDocument you can see that it's constructed using XPathDocumentBuilder class, which implements XmlWriter! Put it another way: XPathDocument internally is constructed using only XmlWriter, but somehow it's impossible to populate it with your own XmlWriter. Weird, huh?

To prove it here is a little hackery showing it's feasible to populate XPathDocument with XmlWriter (it's a rude hack, don't use it):

//Create XPathDocumentBuilder
Type xpathDocBuilderType = 
XPathDocument doc = 
    BindingFlags.NonPublic | BindingFlags.Instance, 
    null, new object[] { }, null);
ConstructorInfo xpathDocBuilderCtor = 
XmlWriter xpathDocBuilder = 
  new object[] { doc, null, "", null });

//Populate XPathDocument
xpathDocBuilder.WriteAttributeString("attr", "value");

The output is
<foo attr="value">content</foo>

I wonder why this useful functionality isn't exposed. Apparently the reason is the added complexity. That would require to expose XPathDocumentBuilder and probably move to Builder pattern of constructing XPathDocument altogether. Ok, I've opened a suggestion at the MSDN Feedback Center, let's see what Microsofties say.