Simon P. Chappell writes "I don't know about you, but I hardly bother with browser bookmarks any more. I used to have so many bookmarks, back in the early days of Netscape's 4 series, that I would have to regularly trim and edit my bookmark file to prevent my browser from crashing on startup -- that's a lot of bookmarks, folks! Now, I go to my favourite web search engine, enter a couple of appropriate search terms and voila, there's my page! Search engines are so ubiquitous that we rarely give much thought to the technology that powers them. Lucene in Action by Otis Gospodnetic and Erik Hatcher , both committers on the Lucene project, goes behind the HTML and takes you on a guided tour of Lucene, one of a generation of powerful Free and Open-Source search engines now available." Read on for the rest of Chappell's review.
Who's it for?Lucene is a library and framework, rather than a complete application. It truly is an engine, around which you are expected to build and extend your own application. Like Lucene, the book is targeted at those who are looking for a tool to build their own search facility application rather than just "download and go." The book does include a number of case studies of Lucene usage (including at least one download and go search engine) but those are included to show how to use and adapt Lucene to fit differing environments rather than as ends in themselves.
The StructureThe book is sensibly divided into two parts. The first part looks at "Core Lucene" functionality, while the second part addresses "Applied Lucene".
Part one has six chapters, covering the central components and inner workings of Lucene. It's here that the book starts with a tutorial introduction, familiarising the reader with the concepts of Lucene as a search engine around which you wrap your own code. The other five chapters move steadily through good search engine fare, with indexing getting the whole of chapter two to itself The discussion of how to retrieve text from the documents being indexed is mentioned here but postponed until chapter seven, where it is dealt with exhaustively. Chapter three covers searching, and especially how Lucene ranks documents.
Chapter four examines analysis. In it's chapter introduction, the book explains that "Analysis, in Lucene, is the process of converting field text into it's most fundamental indexed representation, terms." This process is performed by an analyser, which tokenises text according to it's own built in rules; each analyser will have a different emphasis, some want only dictionary words, others might explicitly include acronyms and sometimes you'll want an analyser that will block stop words (those words in languages that are part of the structure, but that add nothing to the information being conveyed by the text; classic examples of stop words in English include "a", "and" and "the").
Chapter five looks at advanced search techniques; everything from sorting search results, searching on multiple fields to filtering searches. Many free or open source software tools are extensible, and Lucene is no exception. Chapter six addresses creating and using custom components within Lucene, everything from custom sort methods to custom filters.
Part two, the final four chapters, cover Applied Lucene. It is dedicated to practical uses of Lucene and answers the question "So, what can I do with a search engine?" Chapter seven covers ways and means to parse common, non-plain text document formats. The primary formats covered are RTF, XML, PDF, HTML and Microsoft Word. The ability to parse and index these file formats will cover the search engine needs of the majority of Lucene users. Chapter eight looks at a number of Lucene tools and extensions that are available; many of them being free and open source software. Chapter nine covers ports of Lucene. While for many users, Lucene being a Java library is not a problem, some users want its functionality in environments that do not have Java. The chapter looks at ports written in C++, C#, Perl and Python. Lastly, chapter ten takes a thorough look at seven Lucene case studies. Perhaps the "star" case study is the one about Nutch, a download and go search engine written by Doug Cutting , the original author of Lucene.
There are three appendices. The first offers installation advice for Lucene; a useful addition that those newer to working with Java libraries will surely appreciate. The second appendix has a very well explained description of the Lucene index format. This is the kind of information that can be hard to find, so it is welcome in a book of this sort. The last appendix contains a number of categorised resource references. The number and breadth of the resources provided could provide quite an incredible education in information retrieval theory if the reader was inclined to read them all.
What's to Like?There are several things to like about this book. Let's start with the fact that the authors are part of the core development team of Lucene. This gives them both credibility and an excellent understanding of the internal workings of Lucene. Co-author Erik Hatcher is a fantastic writer, having previously been a co-author of the only Ant book worth bothering with, Manning's Java Development with Ant . (Full disclosure: I do know Erik personally.)
The structure of the book is well thought out and each chapter does seem to move your understanding forward when combined with what you learned from the proceeding ones. The division into core and applied Lucene is also helpful. While you'd hope that this was the case, it often isn't; hence I note it as a positive.
I especially appreciate that this book does not fill up page after page with API documentation. The authors appear to have grasped that if you have Internet access to download the software, you might just be able to access the documentation online; rather, they concentrate on the way to use the software. What a concept!
As a part of Manning's "in Action" series, the book has excellent layout and has obviously been thoroughly edited by both technical evaluators and copyeditors. This might seem to be a small thing to some, but a well-edited book stands out clearly from the crowd.
What's to consider?If you are looking for a book on using and configuring a download and go style of search engine, this book would be less suitable. While the case study on Nutch is of good length, it would be too short to useful as a configuration guide.
ConclusionI enjoyed reading this book. If you have any text searching needs, this book will be more than sufficient equipment to guide you to successful completion. Even, if you are just looking to download a pre-written search engine, then this book will provide a good background to the nature of information retrieval in general and text indexing and searching specifically.
You can purchase Lucene in Action from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.