Ch3_Rel_Model - The Relational Model Chapter 3 Instructor:...

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Unformatted text preview: The Relational Model Chapter 3 Instructor: Vladimir Zadorozhny vladimir@sis.pitt.edu Information Science Program 1 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny School of Information Sciences, University of Pittsburgh Why Study the Relational Model? Most widely used model Most widely used model. Vendors: IBM, Informix, Microsoft, Oracle, Sybase, etc. Legacy systems in older models E.G., IBMs IMS Recent competitor: objec -oriented model 2 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Recent competitor: object oriented model ObjectStore, Versant, Ontos A synthesis emerging: object-relational model Informix Universal Server, UniSQL, O2, Oracle, DB2 Relational Database: Definitions Relational database : a set of relations Relational database : a set of relations Relation: made up of 2 parts: Instance : a table , with rows and columns. #Rows = cardinality , #fields = degree / arity. Schema : specifies name of relation, plus name and type of each column. E G Students( sid : string name : string login : string 3 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny E.G. Students( sid : string, name : string, login : string, age : integer, gpa : real). Can think of a relation as a set of rows or tuples (i.e., all rows are distinct). Example Instance of Students Relation sid name login age gpa sid name login age gpa 53666 Jones jones@cs 18 3.4 53688 Smith smith@eecs 18 3.2 53650 Smith smith@math 19 3.8 4 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Cardinality = 3, degree = 5, all rows distinct Do all columns in a relation instance have to be distinct? Relational Query Languages A major strength of the relational model: A major strength of the relational model: supports simple, powerful querying of data. Queries can be written intuitively, and the DBMS is responsible for efficient evaluation. The key: precise semantics for relational queries. Allows the optimizer to extensively re-order 5 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Allows the optimizer to extensively re order operations, and still ensure that the answer does not change. The SQL Query Language Developed by IBM (system R) in the 1970 Developed by IBM (system R) in the 1970s Need for a standard since it is used by many vendors Standards: SQL-86 SQL 89 (minor revision 6 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny SQL-89 (minor revision) SQL-92 (major revision) SQL-99 (major extensions, current standard) The SQL Query Language To find all 18 year old students we can write To find all 18 year old students, we can write: SELECT *...
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This note was uploaded on 12/01/2011 for the course INFSCI 2710 taught by Professor Zadorozhnyy,v during the Winter '08 term at Pittsburgh.

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Ch3_Rel_Model - The Relational Model Chapter 3 Instructor:...

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