# Information Retrieval

- information retrieval
	- deals with the representation, storage, organization of and access to information items
	- is finding material of an unstructured nature that satisfies an information need from within large collections
- differences between databases and information retrieval
	- data are strongly structured × documents are not
	- documents are meant for human interaction, data are meant for the computer
- central elements of IR: documents, information need, satisfaction of the user
- information definition … what a user gets from documents using his own knowledge
- document definition … a trace that a human is sending to another human
- we have a very large set of documents, very imprecise information need and we need to satisfy it very fast
- the system needs to know the format of the document to make sense of it
- main dimensions of documents
	- physical (form) – to read a digital document, you need suitable tools
	- meaning (content) – context is part of the meaning construction
	- social (medium) – there's an intention behind every document
- document forms
	- media
		- text (types: book, article, letter)
		- image (types: x-ray, photograph, graphic)
		- video
		- structured documents
	- documents can consist of different documents
- user query
	- user's information need expressed using a predefined language
- satisfaction
	- system should be simple to use
	- must give the best possible answers, they must be relevant
	- must return reasonable quantities of answers
	- must be fast
- other factors to take into account
	- user's expertise
	- temporal and geographical need
- relevance
	- at document side: document, surrogate, information
	- at user side: information need, request, query
- IR context