Note for Information Retrieval - IR By Abhishek Apoorv

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LECTURE NOTES ON INFORMATION RETRIEVAL SYSTEM IV B. Tech I semester (JNTU) 1

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UNIT-1 COMPUTER SCIENCE AND ENGINEERING INTRODUCTION 1.1 Definition: An Information Retrieval System is a system that is capable of storage, retrieval and maintenance of information. → Information in this context can be composed of following: Text (including numeric and date data) Images Audio Video Other multimedia objects → Of all the above data types, Text is the only data type that supports full functional processing. → The term “item” is used to represent the smallest complete unit that is processed and manipulated by the system. → The definition of item varies by how a specific source treats information. A complete document, such as a book, newspaper or magazine could be an item. At other times each chapter or article may be defined as an item. → The efficiency of an information system lies in its ability to minimize the overhead for a user to find the needed information. → Overhead from a user’s perspective is the time required to find the information needed, excluding the time for actually reading the relevant data. Thus search composition, search execution, and reading non-relevant items are all aspects of information retrieval overhead. 1.2 Objectives The general objective of an Information Retrieval System is to minimize the overhead of a user locating needed information. Overhead can be expressed as the time a user spends in all of the steps leading to reading an item containing the needed information. For example: Query Generation Query Execution Scanning results of query to select items to read Reading non-relevant items etc ... 2

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→ The success of an information system is very subjective, based upon what information is needed and the willingness of a user to accept overhead. → The two major measures commonly associated with information systems are precision and recall. →Pr ecision Number _ Re trieved _ Re levant Number _ Total _ Re trieved Numbe _ Re trieved _ Re levant Re call Number _ Possible _ Re levant 3

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1.3 Overview: Functional 4