chapter 5 - part 1 - CGS 2545: Database Concepts Spring...

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CGS 2545: Database Concepts (Chapter 5) Page 1 Mark Llewellyn CGS 2545: Database Concepts Spring 2010 Chapter 5 – Logical Database Design And The Relational Data Model School of Electrical Engineering and Computer Science University of Central Florida Instructor : Dr. Mark Llewellyn markl@cs.ucf.edu HEC 236, 407-823-2790 http://www.cs.ucf.edu/courses/cgs2545/spr2010
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CGS 2545: Database Concepts (Chapter 5) Page 2 Mark Llewellyn The relational data model is based on the concept of mathematical relations. Codd (the guy who proposed the relational model) was a trained mathematician and he used terminology taken from this discipline, primarily set theory and predicate logic. The Relational Data Model
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CGS 2545: Database Concepts (Chapter 5) Page 3 Mark Llewellyn Relation: A relation is a table (matrix) with rows and columns. Relations hold information about the objects modeled in the db. Attribute: An attribute is a named column of a relation. An attribute is some characteristic of an entity (or relationship) that is modeled in the database. Attributes can appear in any order in a relation. Domain: A domain is the set of allowable values for one or more attributes. Every attribute is defined on some domain. Domains may be distinct for each attribute, or two or more attributes may be defined on the same domain. The Relational Data Model (cont.)
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CGS 2545: Database Concepts (Chapter 5) Page 4 Mark Llewellyn Tuple: A tuple is a row of a relation. Tuples can appear in any order in a relation and the relation will remain the same, and therefore convey the same meaning. Degree: The degree of a relation is the number of attributes it contains. Cardinality: The cardinality of a relation is the number of tuples it contains. Relational database: A collection of normalized relations with distinct relation names. The Relational Data Model (cont.)
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CGS 2545: Database Concepts (Chapter 5) Page 5 Mark Llewellyn An Example Relation staffNo fName lName position DOB salary sn24 Kristy Chivotti manager 1-Oct-64 45000 sa3 Tod Spaude ceo 16-Nov-56 90000 sn69 Debi Alonzo cfo 14-Mar-72 67000 sf22 Michael Schumacher driver 3-Jun-77 9999999 sd8 Keri Thompson manager 5-Jun-78 34000 sx99 Julie Bledsoe manager 16-Dec-63 40000 staff relation attributes degree cardinality
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CGS 2545: Database Concepts (Chapter 5) Page 6 Mark Llewellyn Example Domain Definitions Attribute Domain Name Meaning Domain Definition staffNo staffnumbers set of all possible staff numbers character: size 4, must begin with letter s. fName, lName name set of all possible person names character: size 20 DOB date date person was born date: range from 1-Jan-20, format: dd-mmm-yy salary salaries possible values of staff salaries monetary: 7 digits, range 10,000- 9,999,999 position alljobs set of all possible positions select one from set: {ceo, cfo, coo,manager, asst. manager, driver, secretary}
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CGS 2545: Database Concepts (Chapter 5) Page 7 Mark Llewellyn Alternate Terminology for Relational Model Formal Term Alternative 1 Alternative 2 relation table file tuple row record attribute column field
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chapter 5 - part 1 - CGS 2545: Database Concepts Spring...

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