Dbms 9: Relational Model

Dr. Amiya Ranjan Panda
Assistant Professor [II]
School of Computer Engineering,
Kalinga Institute of Industrial Technology (KIIT),
Deemed to be University,Odisha
Relational Model
KALINGA INSTITUTE OF INDUSTRIAL
TECHNOLOGY
School Of Computer
Engineering
4 Credit Lecture Note 09

Chapter Contents
q Relational Model
q Relational Database
q Relational Data Integrity
q Database Languages
q CODD’s Rule
2

3
Relational Model
Ø Relational data model is the primary data model for commercial data-
processing applications.
Ø A relational database consists of a collection of tables, each of which is
assigned a unique name.
Ø A row in a table represents a relationship among a set of values. Thus, a table is
an entity set and a row is an entity.
Ø The columns or properties are called attributes. For each attribute, there is a
set of permitted values, called the domain of that attribute. Same domain can be
shared by more than one attribute.
Ø Degree is the number of attributes in the relation/ table, where as Cardinality is
the number of tuples or rows in the relation/table.
Ø The attribute values are required to be atomic, i.e. indivisible.
Ø Let D1, D2, and D3 are the domains. Any row of the table consists of a 3-tuple
(v1, v2, v3) where v1 ∈ D1, v2 ∈ D2 and v3 ∈ D3. Thus, the table will
contain only a subset of the set of all possible rows. Therefore, the table is a
subset of D1 x D2 x D3.
Ø Each attribute of a relation has a unique name.
Ø NULL Value is a domain value which is a member of any possible domain.

4
Relational Model
Ø Relational data model is the primary data model for commercial data-
processing applications. Database Schema is the logical design of the database.
If (a1, a2 ...an ) be the attributes, then the relation schema will be
R=(a1,a2 ...an )
Ø Database Instance is the snapshot of the data in the database at a given instant
of time
Ø Relation is denoted by lower case names and Relation Schema is the name
beginning with an uppercase letter

5
Relational Database
Ø Relational database is a database consisting of multiple relations or tables.
The information about an enterprise is broken up into parts, with each relation
storing one part of the information
Ø The normalization process deals with how to design relational schemas.

6
Relational Data Integrity
Ø Candidate key is an attribute or set of attributes that can uniquely identify a
row or tuple in a table. Let R be the relation with attributes a1, a2 ... an . The
set of attributes of R is said to be a candidate key of R iff the following two
properties holds:
ü Uniqueness: At any given time, no two distinct tuples or rows of R have
the same value for ai , the same value for aj...an
ü Minimality: No proper subset of the set (ai , aj ... an ) has the uniqueness
property
Ø The major types of integrity constraints are:
1. Domain Constraints:
ü All the values that appear in a column of a relation must be taken from the
same domain.
ü This constraint can be applied by specifying a particular data type to a
column.
2. Entity Integrity Constraints:
ü The entity integrity rule is designed to assure that every relation has a
primary key, and that the data values for that primary key are all valid.
ü Usually, the primary key of each relation is the first column.

7
Relational Data Integrity…
3. Referential Integrity:
ü In relational data model, associations between tables are defined by using
foreign keys
ü A referential integrity constraint is a rule that maintains consistency
among the rows of two relations
ü The rule states that if there is a foreign key in one relation, either each
foreign key value must match a primary key value in the other table or
else the foreign key value must be NULL
ü A foreign key that references its own relation is known as recursive
foreign key
ü The linking between the foreign key and primary key allows a set of
relations to form an integrated database
4. Operational Constraints:
ü These are the constraints enforced in the database by the business rules
or real world limitations.
ü The linking between the foreign key and primary key allows a set of
relations to form an integrated database

8
Database Languages
Ø DDL (Data Definition Language)
ü DDL is used to define the conceptual schema. The definition includes the
information of all the entity sets and their associated attributes as well as
the relationships between the entity sets.
ü The data values stored in the database must specify certain consistency
constraints. The database systems check these constraints every time the
database is updated.
ü The output of the DDL is placed in the Data Dictionary which contains the
metadata (data about data).
ü The data dictionary is considered to be a special type of table, which can
only be accessed and updated by the database system itself.
ü The database system consults the data dictionary, before querying or
modifying the actual data, for the validation purpose.
ü CREATE, ALTER, DROP, RENAME & TRUNCATE
Ø DML (Data Manipulation Language)
ü DML is used to manipulate data in the database.
ü A query is a statement in the DML that requests the retrieval of data from
the database . SELECT, INSERT, UPDATE & DELETE

9
Database Languages…
Ø DCL (Data Control Languages)
ü DCL allows in changing the permissions on database structures
ü GRANT & REVOKE
Ø TCL (Transaction Control Language)
üTCL allows permanently recording the changes made to the rows stored in a
table or undoing such changes
üCOMMIT, ROLLBACK & SAVEPOINT

10
CODD’s Rule
Ø Codd’s rules are a set of 12 rules proposed by E. F. Codd designed to
define what is required from a database management system in order for
it to be considered relational, i.e. RDBMS. Any database that satisfies
even six rules may be categorized as RDBMS.
Ø Rule0: A relational system should be able to manage databases, entirely
through its relational capabilities
Ø Rule1: Information representation: The entire information is explicitly
and logically represented by the data values of the tables in the relational
data model
Ø Rule2: Guaranteed access: In relational model, at each cell, i.e. the
interaction of each row and column, it will have one and only one value
of data (or NULL value). Each value of data must be addressable via the
combination of a table name, primary key value and the column name
Ø Rule3: Systematic treatment of NULL values: NULL values are
supported in fully relational DBMS for representing missing information
and inapplicable information in a systematic way independent of data
type.

11
CODD’s Rule
Ø Rule4: Database description rule: The database description is
represented at the logical level in the same way as ordinary data, so that
authorized users can apply the same relational language to its
interrogation as they apply to the regular data. This means, the RDBMS
should have a data dictionary
Ø Rule5: Comprehensive data sub-language: The RDBMS should have
its own extension of SQL. The SQL should support Data Definition, View
Definition, Data Manipulation, Integrity Constraint, and Authorization
Ø Rule6: Views updation: All views that are theoretically updatable are
also updatable by the system. Similarly, the views which are theoretically
non-updatable are also non-updatable by the database system.
Ø Rule7: High-level update, insert, deletes: A RDBMS should not only
support retrieval of data as relational sets, but should also support
insertion, updation and deletion of data as a relational set.
Ø Rule8: Physical data independence: Application programs and
terminal activities are not disturbed if any changes are made either in
storage representations or access methods.

12
CODD’s Rule
Ø Rule 9: Logical data independence: User programs and the user
should not be aware of any changes to the structure of the tables such
as the addition of extra columns
Ø Rule10: Distribution independence: A relational DBMS has distribution
independence. The RDBMS may spread across more than one system
and across several networks. However to the end-user, the tables
should appear no different to those that are local.
Ø Rule11: Integrity rule: Integrity rules must be supported by the
relational data sub-language; they can be stored in the catalogue and
not in the application program. Entity integrity: no component of a
primary key may have a NULL value. Referential integrity: for every
unique non-null ’foreign key’ values in the database, there should be a
matching primary key value from the same domain.
Ø Rule12: Data integrity cannot be subverted: If a relational system has
a low-level language, that low level cannot be used to subvert or bypass
the integrity rules and constraints expressed in the higher level relational
language

Dbms 9: Relational Model

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