Chapter2 - Intro to Rdbms
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Transcript of Chapter2 - Intro to Rdbms
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INTRODUCTION TO RDBMS
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Objectives
After completing this chapter, you will be able to:
Define a Relational Database Management System
(RDBMS)
Define a relation
List the features of an RDBMS
List Important terms related to RDBMS
Describe the different types ofkeys and their use
Explain referential integrity
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Basic Definitions
RELATIONAL DATABASE
A relational database is a database system in which
the database is organized and accessed according
to the relationships between data items without
the need for any consideration of physical
orientation and relationship.
Relationships between data items are expressed by
means oftables.
It is a tool which can help you store, manage and disseminateinformation of various kinds. It is a collection of objects, tables,
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RELATIONAL DATABASE MANAGEMENT SYSTEM
It is a system which allows us to perceive data as tables
(and nothing but tables) and operatorsnecessary to
manipulate that data are at the users disposal.
The operators used are:
SELECT
PROJECT
JOIN
Definitions continued...
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Features of RDBMS
The ability to create multiple relations (tables) and
enter data into them.
An interactive query language.Retrieval of information stored in more than one
table.
Provides aCatalogor Dictionary, which itselfconsists of tables ( called system tables )
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Important Terms
Relation : a tableTuple : a row in a table
Attribute : a column in a table
Degree : number of attributesCardinality : number of tuples
Primary Key : a unique identifier for the
tableDomain : a pool of values from which
specific attributes of specific relations draw
their values
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Properties of a Relation (Table)
There are no duplicate rows (tuples).
Tuples are unordered, top to bottom.
Attributes are unordered, left to right.
All attribute values are atomic (or scalar).
Relational databases do not allow repeating
groups.
A database relation is a predefined row/column
format for storing information in a relational
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Keys
Key
An attribute or set of attributes whose values uniquely
identify each entity in an entity set is called a key for
that entity set.
Super Key
If we add additional attributes to a key, the resulting
combination would still uniquely identify an instance
of the entity set. Such augmented keys are called super
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Referential Integrity
It is an integrity constraint which specifies that the value(or existence) of an attribute in one relation depends on
the value (or existence) of an attribute in the same or
another relation.
Referential integrity in a relational database is consistency
between coupled tables.
It is usually enforced by the combination of a primary key
and a foreign key.For referential integrity to hold, any field in a table that is
declared a foreign key can contain only values from a
parent table's primary key field.
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sid cid grade53666 carnatic101 C
53688 reggae203 B
53650 topology112 A
53666 history105 B
sid name age
53666 Jones 18
53688 Smith 18
53650 Smith 19
gpa
3.4
3.2
3.8
login
Jones@cs
Smith@eecs
Smith@math
Enrolled Student
Primary keyForeign key referring tosid of STUDENT relation
Keys and Referential Integrity
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Summary
You now should be able to:
1.Define a Relational Database Management System
(RDBMS)
2.Define a relation
3.List the features of an RDBMS
4.List Important terms related to RDBMS
5.Describe the different types ofkeys and their use
6.Explain referential integrity