One of our bigger sites has a section where users can send questions to the website owner which get evaluated personally by his staff. When the same question pops up very often they can add this particular question to the Faq.
In order to prevent them from receiving dozens of similar questions a day we would like to provide a feature similar to the 'Related questions' on this site (stack overflow).
What ways are there to build this kind of feature? I know that i should somehow evaluate the question and compare it to the questions in the faq but how does this comparison work? Are keywords extracted and if so how?
Might be worth mentioning this site is built on the LAMP stack thus these are the technologies available.
Thanks!