chapter 4 - part 1 - COP 4710: Database Systems (Chapter 4)...

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Unformatted text preview: COP 4710: Database Systems (Chapter 4) Page 1 Mark Llewellyn COP 4710: Database Systems Fall 2009 Chapter 4 Relational Query Languages Part 1 School of Electrical Engineering and Computer Science University of Central Florida Instructor : Dr. Mark Llewellyn markl@cs.ucf.edu HEC 236, 823-2790 http://www.cs.ucf.edu/courses/cop4710/fall2009 COP 4710: Database Systems (Chapter 4) Page 2 Mark Llewellyn A query language is a language in which a database user requests information from the database. Most query languages are on a higher-level than standard programming languages like C and Java. Query languages fall into a category of languages known as 4GL. Query languages can be broadly categorized into two groups: procedural languages and nonprocedural languages. A procedural query language requires the user to specify a sequence of operations on the db to compute the desired result. (User specifies how and what.) A nonprocedural query language requires the user to describe the desired result without needing to specify the sequence of operations required to obtain the result. (User specifies only what.) Query Languages COP 4710: Database Systems (Chapter 4) Page 3 Mark Llewellyn Most commercially available relational database systems offer a query language which is categorized as a hybrid query language. Hybrid query languages include elements of both the procedural and nonprocedural approaches to query languages. For the time being we are going to examine pure relational query languages. These languages are terse and formal and lack many of the syntactic elements available in commercial languages, but they illustrate the fundamental techniques utilized by all query languages for extracting data from the database. Query Languages (cont.) COP 4710: Database Systems (Chapter 4) Page 4 Mark Llewellyn As we examine these pure languages, bear in mind that, although the pure languages do not contain such features, a complete query language has facilities for inserting and deleting tuples from relations as well as for modifying existing tuples. Procedural language: 1. relational algebra Nonprocedural languages: 1. relational tuple calculus 2. relational domain calculus Query Languages (cont.) COP 4710: Database Systems (Chapter 4) Page 5 Mark Llewellyn The relational algebra is a procedural query language. It consists of set operations which are either unary or binary, meaning that either one or two relations are operands to the set operations. Each of the set operations produces a relation as its output. There are five fundamental operations in the relational algebra and several additional operations which are defined in terms of the five fundamental operations....
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This note was uploaded on 11/01/2009 for the course CS cop4710 taught by Professor Dr. mark llewellyn during the Fall '09 term at University of Central Florida.

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chapter 4 - part 1 - COP 4710: Database Systems (Chapter 4)...

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