c#: Strict algorithm or library for text search

Question

The Problem:

I need a good free library or algorithm to determine whether a text is related to a search pattern or not. The search pattern can be an ordered or unordered list of words. For some searches the order is relevant, for some it is not. Additionally I need the ability to define aliases for searched words (e.g. "(C#|C sharp) code").

I doubt that there is a free cheap c# library meeting all my requests.

Which libraries/algorithms would you use to implement that functionality? I´m grateful for any tip.

EDIT: I need this to filter search results from multiple specialized search services. The resulting program must be VERY strict, so false negatives are no problem.False positives should be avoided(as far as possible).

Answer 1

For free, start here with the builtin Regex namespace/class:

http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex.aspx

More sophisticated search is unlikely to come for free (cf. Google Search Appliance or similar).