Mastering Database Management

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Relational Models

Relational Data Model

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 ‘The ‘Relational Database Model is the most common model in industry today. 

 A relational database is based on the relational model developed by E.F. Codd.

 A relational database allows the definition of data structures, storage and retrieval operations and integrity constraints. In such a database the data and relations between them are organized into tables. A table is a collection of records and each record in a table contains the same fields.

Properties of the Relational database model

  •  Data is presented as a collection of relations.
  •  Each relation is depicted as a table.
  •  Columns are attributes that belong to the entity modelled by the table (ex. In a student table, you could have name, address, student ID, major, etc.).
  •  Each row (“tuple”) represents a single entity (ex. In a student table, John Smith, 14 Oak St, 9002342, Accounting, would represent one student entity).
  •  Every table has a set of attributes that taken together as a “key” (technically, a “superkey”) uniquely identifies each entity (Ex. In the student table, “student ID” would uniquely identify each student – no two students would have the same student ID).

Terminology

Tables − In relational data model, relations are saved in the format of Tables. This format stores the relation among entities. A table has rows and columns, where rows represents records and columns represent the attributes.

 Tuple − A single row of a table, which contains a single record for that relation is called a tuple.

Relation instance − A finite set of

tuples in the relational database system represents relation instance. Relation instances do not have duplicate tuples.

Relation schema − A relation schema describes the relation name (table name), attributes, and their names. Shown below

A database schema is the skeleton structure that represents the logical view of the entire database. It defines how the data is organized and how the relations among them are associated.​

 

Relation key − Each row has one or more attributes, known as relation key, which can identify the row in the relation (table) uniquely.

Attribute domain − Every attribute has some pre-defined value scope, known as attribute domain.