XML and Perl (Paperback)

Perhaps it's more suited for students with little or no background knowledge of XML, as it seems to be more of an XML tutorial that happens to use Perl as the language, rather than how to leverage Perl's power to make good XML apps.

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 voered 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 inteface 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 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.

The book goes from event-driven and tree-based parsers, to XML generation and conversion from other file types (including the basic use of XML with relational databases), to introductions to XSLT transformations, AxKit, and SOAP (an introduction to XML-RPC is also promised, but seems to have mysteriously disappeared - the editing is occasionally patchy).

Within this framework the structure is simple: each section introduces a perl xml module, explains where it fits in the general scheme, and gives a practical example. Most of the examples include a DTD, Schema, sample XML file, and a short program making use of the particular module. The dual use of the Schema/DTD is useful if you're in the process of transferring from DTDs to Schemas, but it does make each section rather long.

Overall, this is a good book to use if you're new to the xml/perl combination (a llama rather than a camel). The introductions are clear, the examples seem fine (though I haven't tested them), and the book is good at putting the modules in context. The obvious comparison is with the O'Reilly Perl/XML book, which covers much of the same material at a faster pace and with fewer (more whimsical) examples. Both have their own strengths: this is probably better for beginners, and certainly stronger on examples, but that does mean it sometimes spends a little too much time on the obvious (using print to generate xml, for example) without getting on to more problematic issues such as internationalization with perl and xml. Maybe some day the authors could do a 'part two'?