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Copyright © Genetic Computer School 2009DBSQL 3-1
Chapter 3
Relational Database Model
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-2
Chapter 3 Overview
Relational DatabaseRelational Data ModelKeysRelational IntegrityRelational AlgebraTuple and Domain Relational Calculus
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-3
Relational Database
Relational database those entities will then be represented by tables or shall we say relation. Each attribute in an entity will serve as the column of each relation which can be specified later with some keys and constraints.
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-4
Relational Data Model
Relational Model is composed of tables and its relationship with other tables. Generally it follows the concept of tabular representation of an entity.
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-5
Cont’
Relation
Tuple
Domain
Degree
Cardinality
Is a table with flat files of rows and columns which has certain properties
Is a row of a relation and represents and instance of a relation
Is the set of allowable values for one or more columns
Is the number of attributes it contains
Is the number of tuples it contains
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-6
Keys
Every relation can be identified using a key column or field. These keys are in different types depending on the degree of a column definition and existence.
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-7
Type of Keys
Primary
Foreign
Super
Candidate
Alternate
It is a candidate key that uniquely identifies a relation
It is an attribute key of a relation and also a unique key from another table. This key is used in order to link two tables together.
It is a subset attribute of an entity that will uniquely identify a relation.
Is any set of one or more columns whose combined values are unique among all occurrences (i.e., tuple or row). Alternate keys of any table are simply those candidate keys which are not currently selected as the primary key.
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-8
Relational Integrity
Domain Type Key
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DBSQL 3-9
Relational Algebra
Relational Algebra is a theoretical way of manipulating data in a relational database. This is usually associated with querying the entire database system. It includes operations that act on existing table to produce new table, similar to the way of addition and subtraction act on numbers to produce new numbers.
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-10
Cont’
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-11
Cont’
Relational Algebra
Relational Calculus
It is more operational, and it deals with operational plan used in manipulating the database.
It Lets user define what they want and how they want the data to be.
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-12
Relational Algebra Operations
Set Operations Union Intersection Difference
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DBSQL 3-13
Cont’
Operations that remove parts of a relation
Selection Projection
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DBSQL 3-14
Cont’
Operations that combine tuple from two relations
Cartesian Product Join
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DBSQL 3-15
Relational Algebra - Examples
Selection
R = Select
ColumnName(condition) Relation
Name
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DBSQL 3-16
Cont’
Projection
= Project
= (ColumnName1, ColumnName2….ColumnNamen) Relation Name
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DBSQL 3-17
Cont’
Cartesian Product
The Cartesian product is defined by the concatenation of tuples between two relations. It is usually denoted by multiplication operation (R x S).
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-18
Cont’
Union
This builds a relation consisting of all tuples appearing in either or both of two specified relations. The two relations must be union-compatible, which means that they must have the same number of attributes and these attributes must come from the same domain.
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-19
Cont’
Difference
This operation builds a relation consisting of all tuples appearing the first but not the second of two specified relations.
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-20
Cont’
Intersection
This builds a relation consisting of all tuples appearing in both of two specified relation. Again the two relations must be union-compatible.
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-21
Join Operations
Join Operation
Natural Join
Theta Join
Equi join
Outer Join
Left-Outer Join Right-Outer Join
Full Outer Join
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-22
Advantages and Limitations of Relational Algebra
Relational Algebra is useful specially in query optimization but there are areas in which it cannot be appliedRelational Algebra cannot modify a databaseRelational Algebra cannot perform arithmetic operations
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-23
Tuple and Domain Relational Calculus
Tuple Relational Calculus
It is a form of relational calculus where it tries to find a predicate only if it is true. The common term given to this form is called tuple variable.
Notation
{E | L (E)}
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-24
Cont’
Domain Relational Calculus
Domain relational Calculus uses variables that take values from domains instead of a relation’s tuple. If a domain formulae is composed of atoms F(d1, d2, …, d n) then it can be represented by the variable:
{d1, d2, …, d n | F (d1, d2, …, d n) }
Copyright © Genetic Computer School, Singapore 2009
DBSQL 3-25
End
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