If you want to learn more about learning over text I will recommend you to look at those lectures: http://videolectures.net/mlas06_pittsburgh/

First two lectures are great introduction to this topic and third is also related, but not necessary.

If you want to dive deeper to more advanced stuff I will recommend to look to the conditional random fields, which is kind of state of art of this field right now.

Great tutorial: http://www.cs.umass.edu/~mccallum/papers/crf-tutorial.pdf Wiki entry: http://en.wikipedia.org/wiki/Conditional_random_field