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Information Retrieval First lessons Basic ideas User needs information Information sources Distinguish data, information, knowledge Very well organized, indexed, controlled Totally unorganized, uncharacterized, uncontrolled Something in between Connect the two in a way that matches information needs to information available. The role of databases Databases hold specific data items Organization is explicit Keys relate items to each other Queries are constrained, but effective in retrieving the data that is there Databases generally respond to specific queries with specific results Browsing is difficult Searching for items not anticipated by the designers can be difficult The Web Extreme opposite of a database No organization, no overall structure, no index or key to the content Searching and browsing are supported, but generally are not complete. (You will not know if you got every good response to your request. You may be able to tell that you got the response that meets your need, but may not know if you got the best response available.) Digital Library Something in between the very structured database and the unstructured Web. Content is controlled. Someone makes the entries. (Maybe a lot of people make the entries, but there are rules for admission.) Searching and browsing are somewhat open, not controlled by fixed keys and anticipated queries. Nature of the collection regulates indexing somewhat. How do we know the response is good? Precision Of the results returned, what percentage are meaningful to the goal of the query? Recall Of the materials available that match the query, what percentage were returned? Text: Retrieval process The process sequence Query entered Results Ranked Query Interpreted Index searched Items retrieved The collection Where does the collection come from? How is the index created? Those are important distinguishing characteristics Inverted Index -- Ordered list of terms related to the collected materials. Each term has an associated pointer to the related material(s). CITIDEL An example Digital Library All items are relevant to computing education Visit at http://www.citidel.org Part of the National Science Digital Library http://www.nsdl.org