Ch4a_Algebra - 1 Database Management Systems, R....

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Unformatted text preview: 1 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Relational Algebra Chapter 4, Part A Instructor: Vladimir Zadorozhny vladimir@sis.pitt.edu Information Science Program School of Information Sciences, University of Pittsburgh 2 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Relational Query Languages Query languages : Allow manipulation and retrieval of data from a database. Relational model supports simple, powerful QLs: Strong formal foundation based on logic. Allows for much optimization. Query Languages != programming languages! QLs not expected to be Turing complete. QLs not intended to be used for complex calculations. QLs support easy, efficient access to large data sets. 3 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Formal Relational Query Languages Two mathematical Query Languages form the basis for real languages (e.g. SQL), and for implementation: Relational Algebra : More operational , very useful for representing execution plans. Relational Calculus : Lets users describe what they want, rather than how to compute it. ( Non- operational, declarative .) 4 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Preliminaries A query is applied to relation instances , and the result of a query is also a relation instance. Schemas of input relations for a query are fixed (but query will run regardless of instance!) The schema for the result of a given query is also fixed! Determined by definition of query language constructs. Positional vs. named-field notation: Positional notation easier for formal definitions, named-field notation more readable. Both used in SQL 5 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Example Schema Sailors(sid: integer , sname: string, rating: integer, age:real) Boats(bid: integer , bname: string, color: string) Reserves(sid: integer, bid: integer, day: date)...
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Ch4a_Algebra - 1 Database Management Systems, R....

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