Chapter 3 - Data Relational Model

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CHAPTER 3 : DATA RELATIONAL MODEL

Prepared by : Norzelan bin Saleh


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A database is a collection of information that is organized sothat it can easily be accessed, managed, and updated.

In one view, databases can be classified according to types of

content: bibliographic, full-text, numeric, and images.

What is Database?


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Table: two-dimensional structure composed of rows andcolumns

Components of database table are :Record (tuple) - is a sequence of attributes i.e. a row in the relationtable.

Attribute (field) - is a named column in the relation table.

Domain - The domain of an attribute defines the set of values which canapply to that attribute.

Degree - The degree of a relation refers to the number of attributes in

each tuple.Cardinality - This refers to the number of tuples in the relation

Components of Database Table


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Relation Schema: relation name + attribute names + domain

Relation name

Attribute name

Domains

Characteristic of Relation Scheme


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Consists of one or more attributes that determine otherattributes.

Keys

Primary Key - Primary key (PK) is an attribute (or acombination of attributes) that uniquely identifies any givenentity (row)

Superkey - Any key that uniquely identifies each row

Candidate key - A superkey without redundancies

Composite key - Composed of more than one attribute

Foreign key a field in a relational table that matches theprimary key column of another table. The foreign key can beused to cross-reference tables


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Entity Integrity

Referential Integrity - FK contains a value that refers to an existing validtuple (row) in another relation

Integrity Rules


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Relational Model Relationship


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One entityrelated toanother ofthe sameentity type

Entities oftwo differenttypes relatedto each other

Entities of three

different typesrelated to eachother


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Each entity in the relationship will have exactly one relatedentity

One to Many Relationship


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Entities on both sides of the relationship can have many relatedentities on the other side

Many to Many Relationship


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Converting the M:N relationship into TWO 1:M relationships

Foreign keys reference the primary keys in the other

tables of which it has a relationship with

The database designer has 2 main options to definea composite tables primary key: either

use the combination of those foreign keys orcreate a new primary key.


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Self-referencing relationships are a special case of a normal

table relationship.

The only difference is that in this case, there is only one tableinvolved and it is on both sides of the relationship.

Example :One common example is an Employees table that contains informationabout the supervisor of each employee. Each supervisor is also anemployee and has his or her own supervisor. In this case, there is a one-to-many self-referencing relationship, as each employee has onesupervisor but each supervisor may have more than one employee.

Self Referencing Relationship


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Relational algebra

Defines theoretical way of manipulating table contents using relationaloperators

Use of relational algebra operators on existing tables (relations)produces new relations

Relational Database Algebra

Restrict (select) Project

Join (outer, inner)Cartesian Product


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Yields values for all rows found in a table

Can be used to list either all row values or it can yield only those rowvalues that match a specified criterion

Yields a horizontal subset of a table

Select


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Yields all values for selected attributes

Yields a vertical subset of a table

Project


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Allows information to be combined from two or more tables

Real power behind the relational database, allowing the use of

independent tables linked by common attributes

Join


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Outer join:

Matched pairs are retained and any unmatched values in other tableare left null

In outer join for tables CUSTOMER and AGENT, two scenarios arepossible:

Left outer joinYields all rows in CUSTOMER table, including those that do nothave a matching value in the AGENT table

Right outer join

Yields all rows in AGENT table, including those that do not havematching values in the CUSTOMER table


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Inner Join

An inner join (sometimes called a simple join) is a join of two or more

tables that returns only those rows that satisfy the join condition.

Traditional inner joins look for rows that match rows in the othertable(s), i.e. to join two tables based on values in one table being equalto values in another table

Also known as equality join, equijoin or natural join

Returns results only if records exist in both tables


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Database Systems: Design, Implementation, &

Relational Algebra Operators (continued) Union:

Combines all rows from two tables, excluding duplicaterows

Tables must have the same attribute characteristics Intersect:

Yields only the rows that appear in both tables


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Database Systems: Design, Implementation, & Management, 7th

Edition, Rob & Coronel

Relational Algebra Operators(continued)


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Relational Algebra Operators (continued) Difference

Yields all rows in one table not found in the othertable that is, it subtracts one table from theother

Product Yields all possible pairs of rows from two tables

Also known as the Cartesian product


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Relational Algebra Operators

(continued)


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Relational Algebra Operators (continued)

DIVIDE requires the use of one single-columntable and one two-column table


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th

Relational Algebra Operators

(continued)

Chapter 3 - Data Relational Model

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