ch19 - Chapter19: Silberschatz,KorthandSudarshan...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
<number> Database System Concepts ©Silberschatz, Korth and Sudarshan See  www.db-book.com  for conditions on re-use  Chapter 19:  Information Retrieval Chapter 19:  Information Retrieval
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
©Silberschatz, Korth and Sudarshan 19.<number> Database System Concepts - 5 th  Edition, Sep 2, 2005 Chapter 19: Information Retrieval Chapter 19: 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
Background image of page 2
©Silberschatz, Korth and Sudarshan 19.<number> Database System Concepts - 5 th  Edition, Sep 2, 2005 Information Retrieval Systems 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 e.g., 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
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
©Silberschatz, Korth and Sudarshan 19.<number> Database System Concepts - 5 th  Edition, Sep 2, 2005 Information Retrieval Systems (Cont.) 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
Background image of page 4
19.<number> Database System Concepts - 5 th  Edition, Sep 2, 2005 Keyword Search Keyword Search In  full text  retrieval, all the words in each document are considered to be  keywords.  We use the word  term  to refer to the words in a document Information-retrieval systems typically allow query expressions formed using  keywords and the logical connectives  and, or,  and  not And s are implicit, even if not explicitly specified Ranking of documents on the basis of estimated relevance to a query is critical Relevance ranking is based on factors such as Term frequency Frequency of occurrence of query keyword in document Inverse document frequency How many documents the query keyword occurs in  » Fewer 
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 25

ch19 - Chapter19: Silberschatz,KorthandSudarshan...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online