Data Relation Model

1. Intergrity Rule

1.1. Definition

1.2. Image

2. Relational Operator

2.1. Definiton

2.2. Function in DBMS

3. Definition

3.1. A relational database management system (RDBMS) is a program that lets you create, update, and administer a relational database. Most commercial RDBMS's use the Structured Query Language (SQL) to access the database, although SQL was invented after the development of the relational model and is not necessary for its use.

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4. Characteristic of Relational Table

4.1. A table is perceived as two dimensional structure composed of rows and colums

4.2. Each table row (tuple) represents a single entity occurence within the entity set

4.3. Each table colums represents an attribute and each column has a distinct name.

4.4. Each row/column intersection represents a single data value

4.5. All values in a column must conform the same data format

4.6. Each column has specific range of values known as the attribute domain

5. Key

5.1. Definition

5.2. Composite key

5.2.1. Composed of more than one attribute

5.3. Key Attribute

5.3.1. Any attribute that is part of a key

5.4. Superkey

5.4.1. Any key that uniquely identifies each row

5.5. Candidate key

5.5.1. A superkey without unnecessary attributes