ics321-20090908-relational1

ics321-20090908-relational1 - ICS 321 Fall 2009 The...

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ICS 321 Fall 2009 The Relational Model (i) Asst. Prof. Lipyeow Lim Information and Computer Science Department University of Hawaii at Manoa 9/8/2009 1 Lipyeow Lim -- University of Hawaii at Manoa
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Review ER model models the application data at the conceptual level it does not assume any data model at the logical level A rigorous way to reason about ER is using set theory / Venn diagrams Entity sets are collections of entities Relationship sets are collections of edges connecting entities of entity sets Relational model logical database design 9/8/2009 Lipyeow Lim -- University of Hawaii at Manoa 2
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Why Study the Relational Model? Most widely used model. Vendors: IBM, Informix, Microsoft, Oracle, Sybase, etc. “Legacy systems” in older models E.g., IBM’s IMS Recent competitor: object-oriented model ObjectStore, Versant, Ontos A synthesis emerging: object-relational model Informix Universal Server, UniSQL, O2, Oracle, DB2 9/8/2009 3 Lipyeow Lim -- University of Hawaii at Manoa
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Relational Database: Definitions 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, age : integer, gpa : real). Can think of a relation as a set of rows or tuples (i.e., all rows are distinct). 9/8/2009 4 Lipyeow Lim -- University of Hawaii at Manoa
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Example Instance of Students Relation Cardinality = 3, degree=5, all rows distinct Do all columns in a relation instance have to be distinct? 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
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Relational Query Languages 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 operations, and still ensure that the answer does not change. 9/8/2009 6 Lipyeow Lim -- University of Hawaii at Manoa
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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) SQL-92 (major revision)
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This note was uploaded on 11/15/2010 for the course ICS 321 taught by Professor Lim during the Fall '09 term at University of Hawaii, Manoa.

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ics321-20090908-relational1 - ICS 321 Fall 2009 The...

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