getting popular or relevant words from input for use as tags

We all know how tagging on SO works. We make a post, tag it and it helps in searches and is used in folksonomy.

this is what I want to do. Instead of forcing people to tag posts, I can somehow fetch relevant words from th开发者_JAVA百科e post to use as tags.

Apart from say, fetching repeating words, is there a method of getting words of relevance from a post? Maybe a language parser which can detect words of import?

Please give me your own ideas. It doesn't have to be along the lines I am thinking. Thanks.

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Make a table that is a look-up for your keywords. Then search the text entries against your list for hits.

Since you presumably want your tags generated on-the-fly, you would need a large list of words. Those are easy to find (search on "word list"). Then you can delete words of little interest, or even rank them according to relevance.