Relational Data Model

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Relational Data Model

• Lei Li
• CS157B

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Whats a data model?

• Data model is a notation for describing data or
  information.
• The description generally consists of three
  parts
• ---------------Structure of the data
• ---------------Operation on the data
• ---------------Constraints on the data

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The most important data models

• The relational data model
• including object-relational model
• The semistructured-data model
• including XML and related standards

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Basics of the relational model

• 1. Attributes
• 2. Schemas
• 3. Tuples
• 4. Domains
• 5. constraints

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Relational model illustrated
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Defining a relation Schema in SQL

• SQL (pronounced as sequel) is the principal
  language used to describe and manipulate
  relational database.
• Relations in SQL
• 1. stored relation------ tables
• 2. views------- relations defined by a
  computation
• 3. Temporary tables----- constructed by the SQL
  language processor when it performs its job of
  executing queries and data modifications. Got
  thrown away and never stored.

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Data types

• Char
• Bit
• Boolean
• Int
• Float
• Date, Time

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Table declarations

• Create Table table name (
• title CHAR(100),
• year INT,
• length INT,
• genre CHAR(10),
• )

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Simple table
title year length genre

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Modifying relation schemas

• 1. drop table R
• 2. Alter table movies ADD producer INT
• 3. Alter Table Movies Drop length

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Relational Algebra

• Its the data-manipulating aspect of the
  relational model
• Its the core of SQL language and every query in
  SQL gets translated to relational algebra.

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Overview of relational algebra

• The usual set operations-------- union,
  intersection, difference
• Operations that remove parts of a
  relation------selection, projection
• Operations that combine the tuples of two
  relations
• ------------cartesian product, natural join,
  theta join
• Operations called renaming