XTech 2006 - Thursday

Link: http://xtech06.usefulinc.com/schedule#d2006-05-18

Same story. Trying to sleep off cold. Thursday was mostly in the browser technology stream, starting with the second seminar.

Daniel Glazman really believes in Etna (talk | project home). It's always good to hear someone who's both passionate and technically competent talk.

Etna is an open source XML editor, wysiwyg (using CSS). It is being built to allow non-techies to write XML reports, so its non-functional requirements include being able to be used by people with no wish to learn XML.

It uses its own RelaxNG engine, with extensions to provide initial content, and mappings for key events (such as ending a list when the user presses [↵] twice).

Further RNG extensions for external doctypes, processing instructions, label and description of content, localisation properties, and behavioural semantics. By behavioural semantics, Etna allows you to specify tabular, list, outline or block style editing controls - although the CSS could make any XML look like any of these, the idioms the user uses to navigate and edit such content varies, and Etna supports these idioms.

All operations in Etna yield valid XML - gone are such low level operations such as renaming a div tag to a paragraph tag - instead it uses pattern matching to transform between content models, preserving the text content and a maximum amount of structure. This approach was somewhat contentious with some of the audience, since it isn't obvious that it will allow all the operations an old sgml hack would want to do in emacs, but it is the right thing to do in a wysiwyg editor, and I think it's the right thing for a DSL editor too. (* TME: Though for a DSL, I would want the editor to use a different presentation HTML or XUL tree than the XML representation of the AST, and to be able to modify the type labels of the AST based on the text content, which is beyond where Etna is at the moment.)

Mark Birbeck gave a talk about building rich, encapsulated widgets using XBL, XForms and SVG. As before, no mention of breaking the SVG presentation apart into layers, nor how to cope with removing content from the document tree and losing the bindings, but still interesting to see other things you can do with what's available.

Thomas Meinike gave a talk about SVG under Firefox 1.5; nothing new, but he's collected some reference material.

Ryan King gave a talk on the design of microformats (I'll ignore his USA parochial title). Basically - don't repeat yourself + pave the cow-paths. Reuse existing HTML and annotate with semantics, allowing convergence and openness and a very low entry point.

When designing a new microformat, he asked these questions:

• Is there an HTML element that will work?


• Is there an HTML compound that will work?


• Is there an existing microformat that will mostly work?


• Are there any existing standards which are both established and interoperable?

If the answer's yes to any of them, then you don't create a new microformat.

When creating microformats, take a large sample of the existing documents on the web that contain information of the type you are trying to add semantic annotations to. Design your format so that it's in keeping with the consensus of those documents.

After that, I took myself away from the browser crowd and went to hear Benoît Marchal on UML modelling for XML. His main points were

• Integrate XML schema into the rest of the design using the same UML toolset


• Non-UML tools favour hierarchic schemata; UML allows more horizontal relations so can get a better data model


• Use the UML tool as a database with a graph-based front end, not just a drawing tool.


• Use XSLT on XMI to generate the schema. Use an XSLT pipeline, with an intermediate form to simplify the XMI and standardise it across tools.

(* TME: Although I think most current UML tools are poor from a usability stand point, and the lack of denotational semantics in UML2 and laxity in the XMI2 standard restrict model portability, I sympathise with most of what Benoît was saying. I also tend to go further and use XSLT for code generation instead of any vendor specific MDA implementation, again for portability and independence. Some of what he said about schema generation is specific to W3C XSD, and since I work on largely greenfield development I live in a RNG world, aren't as pressing *)

Next up on the browser track was Dean Jackson of the W3C, who is working with the industry to update web standards, such as XMLHttpRequest (why one acronym is all caps and the other is camel cased, I'll never know).

Then came XForms: an alternative to Ajax? You can do some things declaratively using XForms rather than procedurally using JavaScript. The same synchrony and complex rendering issues apply as to XBL.


That was the end of the day at 17:30, and after staying a while at drinks, I went to my room for a nap. Got thinking about yesterday's schema validation talk and today's Etna and other browser stuff, ordered pizza and coffee from room service and started hacking this, getting to bed around 5am.


TME