Relation and difference between information retrieval and information extraction? From Wikipedia 


  Information retrieval is the activity of obtaining information resources relevant to an information need from a collection of information resources. Searches can be based on metadata or on full-text indexing.


From Wikipedia


  Information extraction (IE) is the task of automatically extracting structured information from unstructured and/or semi-structured machine-readable documents. In most of the cases this activity concerns processing human language texts by means of natural language processing (NLP). Recent activities in multimedia document processing like automatic annotation and content extraction out of images/audio/video could be seen as information extraction.


What are the relations and differences between information retrieval and information extraction? 

Thanks!
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)