Textual data is unstructured, unlike the rigidly structured data in relational databases. The term information retrieval generally refers to the querying of unstructured textual data. Information-retrieval systems have much in common with database systems, in particular, the storage and retrieval of data on secondary storage. Chapter 21 describes information-retrieval techniques for querying textual data, including hyperlink-based techniques used in Web search engines. | Chapter 21: Information Retrieval Database System Concepts, 6th Ed. ©Silberschatz, Korth and Sudarshan See for conditions on re-use Chapter 21: Information Retrieval Relevance Ranking Using Terms Relevance Using Hyperlinks Synonyms., Homonyms, and Ontologies Indexing of Documents Measuring Retrieval Effectiveness Web Search Engines Information Retrieval and Structured Data Directories Database System Concepts - 6th Edition ©Silberschatz, Korth and Sudarshan Information Retrieval Systems Information retrieval (IR) systems use a simpler data model than database systems Information organized as a collection of documents Documents are unstructured, no schema Information retrieval locates relevant documents, on the basis of user input such as keywords or example documents ., find documents containing the words “database systems” Can be used even on textual descriptions provided with non-textual data such as images Web search engines are the most familiar example of IR systems Database System Concepts - 6th Edition ©Silberschatz, Korth and Sudarshan Information Retrieval Systems (Cont.) Differences from database systems IR systems don’t deal with transactional updates (including concurrency control and recovery) Database systems deal with structured data, with schemas that define the data organization IR systems deal with some querying issues not generally addressed by database systems Approximate searching by keywords Ranking of retrieved answers by estimated degree of relevance Database System Concepts - 6th Edition ©Silberschatz, Korth and Sudarshan Keyword Search In full text retrieval, all the words in each document are considered to be keywords. Information-retrieval systems typically allow query expressions formed using keywords and the logical connectives and, or, and not We use the word term to refer to the words in a document Ands are
