Apache Lucene 3.0 Tutorial by Bob Carpenter.
At 20 pages it isn’t your typical “Hello World” introduction. 😉
It should be the first document you hand a semi-technical person about Lucene.
Discovering the vocabulary of the documents/domain for which you are building a topic map is a critical first step.
Indexing documents gives you an important control over the accuracy and completeness of information you are given by domain “experts” and users.
There will be terms that are transparent to them and can only be clarified if you ask.