Lexical Analysis libraries

Question

I would like to make a piece of software able to regognize whether a sentence is positive or negative.

Is there any Lexical Analysis libraries arround?

I don't really know where I should start.

Answer 1

The standard name for this task is sentiment analysis

Answer 2

This field is called Natural Language Processing, and it's an incredibly complex subject - not only do you have to parse the words that are positive/negative, but you need to parse modifiers, too (e.g. "Something is not bad").

As usual Wikipedia has some information. If you're just having a bit of fun with this, I suggest trying out a simple system (e.g. recognize "good" and "bad" and "not") and build it up.