Relation and difference between information retrieval and information extraction?
Information retrieval is based on a query - you specify what information you need and it is returned in human understandable form.

Information extraction is about structuring unstructured information - given some sources all of the (relevant) information is structured in a form that will be easy for processing. This will not necessary be in human understandable form - it can be only for use of computer programs.

Some sources:


Information Extraction vs Information Retrieval
From  Information Retrieval to Information Extraction
Information    Extraction Stanford PPT
Introduction to Information Retrieval(link to place in the book with definition)