XML and Perl

davorg writes "One of Perl's great strengths is in processing text files. That is, after all, why it became so popular for generating dynamic web pages -- web pages are just text (albeit text that is supposed to follow particular rules). As XML is just another text format, it follows that Perl will be just as good at processing XML documents. It's therefore surprising that using Perl for XML processing hasn't received much attention until recently. That's not saying that there hasn't been work going on in that area -- many of the Perl XML processing modules have long and honourable histories -- it's just that the world outside of the Perl community doesn't seem to have taken much notice of this work. This is all set to change with the publication of this book and O'Reilly's Perl and XML." Read on to see how well Davorg thinks this book introduces XML text processing with Perl to the wider world. XML and Perl author Mark Riehl, Ilya Sterin pages 378 publisher New Rider rating 8 reviewer Davorg ISBN 0735712891 summary Good introduction to processing XML with Perl

XML and Perl is written by two well-known members of the Perl XML community. Both are frequent contributors to the "perl-xml" mailing list, so there's certainly no doubt that they know what they are talking about. Which is always a good thing in a technical book.

The book is made up of five sections. The first section has a couple of chapters which introduce you to the concepts covered in the book. Chapter one introduces you separately to XML and Perl and then chapter two takes a first look at how you can use Perl to process XML. This chapter finishes with two example programs for parsing simple XML documents.

Section two goes into a lot more detail about parsing XML documents with Perl. Chapter three looks at event-driven parsing using XML::Parser and XML::Parser::PerlSAX to demonstrate to build example programs before going to talk in some detail about XML::SAX which is currently the state of the art in event-driven XML parsing in Perl. It also looks at XML::Xerces which is a Perl interface to the Apache Software Foundation's Xerces parser. Chapter four covers tree based XML parsing and presents examples using XML::Simple, XML::Twig, XML::DOM and XML::LibXML. In both of these chapters the pros and cons of each of the modules are discussed in detail so that you can easily decide which solution to use in any given situation.

Section three covers generating XML documents. In chapter five we look at generating XML from text sources using simple print statements and also the modules XML::Writer and XML::Handler::YAWriter. Chapter six looks at taking data from a database and turning that into XML using modules like XML::Generator::DBI and XML::DBMS. Chapter seven looks at miscellaneous other input formats and contains examples using XML::SAXDriver::CSV and XML::SAXDriver::Excel.

Section four covers more advanced topics. Chapter eight is about XML transformations and filtering. This chapter covers using XSLT to transform XML documents. It covers the modules XML::LibXSLT, XML::Sabletron and XML::XPath.

Chapter nine goes into detail about Matt Sergeant's AxKit, the Apache XML Kit which allows you to create a website in XML and automatically deliver it to your visitors in the correct format.

Chapter ten rounds off the book with a look at using Perl to create web services. It looks at the two most common modules for creating web services in Perl - XML::RPC and SOAP::Lite.

Finally, section five contains the appendices which provide more background on the introductions to XML and Perl from chapter one.

There was one small point that I found a little annoying when reading the book: Each example was accompanied with a sample of the XML documents to be processed together with both a DTD and an XML Schema definition for the document. This seemed to me to be overkill. Did we really need both DTDs and XML Schemas for every example. I would have found it less distracting if one (or even both) of these had been moved to an appendix.

That small complaint aside, I found it a useful and interesting book. It will be very useful to Perl programmers (like myself) who will increasingly be expected to process (and provide) data in XML formats.

You can purchase XML and Perl from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.

Comments

Petal

[Chris Croome]

One new, and cool, Perl XML module that people might not know about is Petal (PErl Template Attribute Language).

It is an implementation of the Zope TAL (Template Attribute Language) specification and it basically allows you to create XML templates where all the templating commands are just attributes of existing tags.

This allows things like XHTML templates which are very WYSIWYG friendly since the editors don't do anything with attributes that they don't know about.

Re:Nice

[DaRobin]

Would be nice to have a book with more than just one chapter on web services.

You might be interested in Programming Web Services with Perl then.

Re:Natural?

[mortonda]

Not really. If you're using XML as "just another text format", then you're making a funamental mistake. Within your software, you should always be treating XML as a hierarchical data structure, not as a text stream. Apart from manipulating CDATA or attribute value text, Perl has no particular strength with XML.

Indeed, the perl only XML libraries are quite slow. I believe most of the quality perl XML handling is done by modules that use C libraries to do the grunt work. However, if the data in the XML itself is text data, then of course, perl and XML are a good match. Add SOAP and mod_perl into the mix, and you got some very nifty tools.

Re:XML frees us from Perl

[DaRobin]

Not much help? If you start counting the number of Perl modules that expose a SAX interface to non-XML data (not to mention the host of other super-useful SAX tools) you'll probably find only one egal, Python.

And if you think that XML has freed us from additional text processing, you obviously haven't used XML much, or at least without much variety. Most people seem constantly bent on including microlanguages in attribute values or text content. Those need good text processing.

Re:If you REALLY want to buy the book

[graxrmelg]

But if people are interested in getting a good price rather than putting a commission into your pocket (and contributing to a company that abuses software patents), maybe they should order it from Bookpool instead, for $3 less than Amazon. (I don't have any affiliation with Bookpool.)

Re:If you REALLY want to buy the book

[Badger]

Actually, /. used to link to Amazon, and had an affiliate program. Once Amazon started enforcing their one-click patent, and the Amazon boycott began, /. switched to Fatbrain (which was bought by BN).

hasn't received much attention until recently?

[HealYourChurchWebSit]

The reviewer is correct, Perl is a good tool for slamming and jammin' text, including XML. What I'm not so sure of is the quote "It's therefore surprising that using Perl for XML processing hasn't received much attention until recently."

I mean one need only scroll down the extensive list of CPAN Modules to see well over 50, as well as many sites/authors devoting time, energy and resource.

Similarly, I would point out some press modules supporting web services via XML, such as SOAP::Lite as far back as 02/26/01 and XML-RPC also in '01 -- or O'Reilly's own XML.com with articles such as "Processing XML with Perl" written shortly after the turn of the millenium.

Point is, though I personally love Perl, blatant plugs such as "... it's just that the world outside of the Perl community doesn't seem to have taken much notice of this work. This is all set to change with the publication of this book and O'Reilly's Perl and XML." " don't inspire confidence in the reviewer's objectivity.

Axkit, perl & XML so happy together

[porter235]

check it out. http://axkit.org/

"Apache AxKit is an XML Application Server for Apache. It provides on-the-fly conversion from XML to any format, such as HTML, WAP or text using either W3C standard techniques, or flexible custom code. AxKit also uses a built-in Perl interpreter to provide some amazingly powerful techniques for XML transformation."

picture coccoon for perl. using perl for xsp pages and doing pipline transformations on xml. great stuff.