Firefox Hacks [Electronic resources] نسخه متنی

Hack 59. Get Tools for XML Validation

Complement your XML content development
processes with life-saving tools.

XML
content is interpreted rather than compiled by Firefox. If XML is
interpreted by a nonvalidating parser, only basic syntax errors are
reported. This hack shows how to check your XML content more
thoroughly.

There is no DTD or XML schema for either Mozilla's XUL or Mozilla's XBL dialects of XML.

6.3.1. Built-In XML-Checking Tools

Firefox's strict XML parser [Hack #58] checks all
XML
content for well-formedness. If the content is to be displayed as a
document and it contains a simple syntax error, Firefox will display
an error. This sample code has incorrectly nested tags:

<?xml version="1.0"?>
<foo>
<bar>
</foo>
</bar>

Figure 6-1 shows the error message that Firefox
reports.

Figure 6-1. A standard XML error message

The problem is that Firefox reports these messages only if the XML
content is destined for display. There's no handy
feedback if the content is delivered into an
existing document. Examples of content delivered into an existing,
displayed document include RSS feeds, RDF datasources, XBL bindings,
and SOAP messages. A simple test strategy is to manually load such
XML directly into the browser using a URL or filename and see what
happens.

Firefox's strict XML parser is not a validating
parser. It doesn't check content against DTDs or
schemas. This means that well-formed XML (or HTML)
isn't checked for valid tags
(entities). You have to use a separate tool for
such a check. The forthcoming E4X support in JavaScript supports only
the five standard entities defined by the base XML standard.

6.3.2. Web-Based Validation Tools

To validate your
XML
code, you can send it to a web site that provides a validation
service. There are several styles of content submission. The
following page-based service provides checking based on a tool called
RXP. You can cut and paste your own URL
into the displayed HTML form, and it will be checked for you:

http://www.cogsci.ed.ac.uk/~richard/xml-checkl

This alternate service lets you upload a local file, use a URL, or
paste an XML content fragment into its submission form:

http://www.stg.brown.edu/service/xmlvalid/

6.3.3. Third-Party Validation Tools

You can pay a fortune for a GUI tool that does XML validation for
you. Here are two products for Windows, both of which offer free
trial versions:

XML Spy http://www.xmlspy.com)

This is a programmer-focused integrated development environment (IDE)
tool with XML-validation features.

Schematron Validator (http://www.topologi.com)

This is a tool focused on data modeling and on editing and checking
XML schema specifications and XML schema instances (XML documents).

Most software tool vendors with an XML focus include validation of
some kind in their commercial offerings.

On Linux/Unix, quality GUI-based tools are less common. Of the GUI
options available, the two main editors, Emacs and
vi (vim is a modern
vi offering) are both troublesome. Expect lots of
web research and configuration time. Both editors support simple
syntax-highlighting out of the box, but that is not validation.

Things are better at the command line, where libraries like
libxml and expat have been
built on to provide useful tools. I recommend these:

XMLStarlet http://xmlstar.sourceforge.net)

This is a set of XML validation tools with a syntax environment
similar to cvs, except all commands are kicked off
via the xml command. XMLStarlet is quick on the
command line and can be easily integrated with makefiles, scripts,
and other simple automations.

Raptor (http://www.librdf.org/raptor/)

RDF overlays plain XML and XML schema content with an additional data
model designed to represent arbitrary relationships between data. A
simple validator is not always enough for RDF; Raptor requires
compilation from source. A useful command-line tool called
rapper analyzes RDF XML content from an RDF point
of view.