Information Retrieval

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Information Retrieval

• First lessons

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Basic ideas

• User needs information
• Distinguish data, information, knowledge
• Information sources
• 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.

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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

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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.)

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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.

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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?

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Text Retrieval process
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The process sequence
Query entered
Results Ranked
Query Interpreted
Index searched
Items retrieved
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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).

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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

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