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Perl Lecture Notes - June 1, 2002 - XML take 2

• Questions

• Summary of (3) perl assignments for this trimester
  1. May 4: GUI / LDAP
  2. May 18: perl-ish XML
  3. June 1: - optional - AxKit (this week)
  4. June 15: SOAP-Lite
  5. June 28: - optional -
  6. July 13: - optional -
  7. July 27: Capstone Presentations

• web publishing with AxKit
  • What it is
    • Apache/mod_perl handler that transforms XML to HTML or whatever.
    • Does several kinds of transformations: XSLT, XPathScript, XSP, custom SAX
    • 

  • Installation and Configuration
    • AxKit.pm is just a perl module - but it has a lot of dependencies on other XSL transform engines and what-not.
    • installation details
    • Configuration is from with apache's httpd.conf, like the mod_perl handler stuff we've seen before.
    • axkit.conf ("Include"-ed from httpd.conf)
    • All and all this is is a PITA (as Brandt would say).
      In particular, the documentation is not at all clear, and the examples didn't work easily.
      I had to do a lot of trial-and-error and staring at the source, and turning on the debugging, and looking at /home/httpd/logs/error_log .
    • To work with this system you really need to have a feel for the Apache/mod_perl stuff.

  • How it works
    • Browser requests http://..../file.xml
    • A transformation mechanism(s) is set by axkit.conf or <?xml-stylesheet...> or agent type (browser vs phone)
      Transformations include
      • XSL - as specified in some file.xsl
      • XPathScript - perl-ish language similar to XSL, mostly specific to AxKit - as specified in some file.xps
      • XSP - ASP/JSP-like tag libraries of functions (including user-defined ones) to generate dynamic content, including session management, cookies, authorization, SQL database queries, and so on. (XSP is from the Cocoon Apache/Java project; this is a perl implementation that uses perl syntax for the <xsp:logic ...> tags. )
      • other SAX filters or pipes or custom transformations
    • Final output is .html or .txt or .pdf or .jpeg or whatever, depending on the nature of the original xml source and transformation.

  • Examples
    • Configuration for all these is axkit.conf.
    • Note that all URI's with /axkit/ go through AxKit. I have aliases /not-axkit/ to the same directory, giving a second URI path that avoids AxKit.

    • Camel - xml to html conversion
      • using XSL (yet another language to learn, eh?)
        • xml source
        • xsl stylesheet
        • output
      • using XPathScript - a perl-ish XPath and XSL
        • xml source
        • xps "stylesheet"
        • output

    • XSP - eXtensible Server Pages.
      This example shows a pipeline: xsp -> xsl -> html
      • xml (xsp) source
      • xsl to html stylesheet
      • output

    • docbook and WAP/WML
      • A more realistic example. DocBook is an established xml format for books. Here we can display that in several ways: screen, printer, handheld. This example uses XPathScript for the transformation. The stylesheet version is chosen either by (1) ?title=printer URI arguments, or (2) by the HTTP request parameters.
      • docbook xml source
      • screen (i.e. web browser) : output | XPathScript
      • print (i.e. all on one page) : output | XPathScript
      • handheld : poor-mans-handheld | wapalizer | XPathScript

    • AxPoint
      
      • Another fairly realistic example. This one converts an xml syntax into a .pdf slideshow presentation, using a SAX processor which can be called from AxKit.
      • source
      • pdf presentation
        (Best viewed with Acrobat's Reader. Save this link as example.pdf if your browser doesn't launch a .pdf viewer correctly.)
      • XML-Handler-AxPoint.pm - perl SAX handler code that does the transformation

• Resources and Documentation
  • acronyms
  • General XML and Perl
    • Perl and XML Kip Hampton's column at O'Reilly's www.xml.com
    • Processing XML with Perl
      (April 5, 2000 - somewhat dated but still nice review of XML and Perl by Michel Rodriguez)
  • AxKit
    • http://axkit.org/
    • http://xml.apache.org
    • AxKit.pm
    • various AxKit component docs from CPAN
    • Introducing AxKit (March 2002 Barrie Slaymaker article)
    • AxKit: XML Web Publishing with Apache and mod_perl by Matt Sergeant
    • XPathScript Guide
    • XSP, Taglibs, and Pipelines (April 16, 2002 Barry Slaymaker article on XSP in AxKit)
  • SAX
    • Transforming XML with SAX Filters (Oct 10, 2001 Kip Hampton article)
  • AxPoint - PDF presentations from XML
    • http://axpoint.axkit.org/
    • XML::Handler::AxPoint.pm
    • using AxPoint in AxKit
  • DocBook - an XML system for structured documents
  • WAP and WML - HTTP and HTML for handhelds

• Assignmnent
  • Work on capstones
  • Browse through the articles and documentation above.
  • Some suggested things to do to get familiar with some of this.
    **Entirely optional**
    • Install AxKit
    • Work though - install, alter - any of the online examples.
    • Play around with AxKit on bob (any directory with /axkit/ in path). You can, I think, add configuration instructions in an .htaccess file.
    • Write a SAX filter to do some XML processing on your data.
    • Write some pages that can be displayed on a handheld or phone, similar to what I did with docbook.

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So there.