Database Model ( DBMS )

Database Models

· A data model is a collection of logical constructs used to represent data structure

and relationship within the database.

· A database model is used to represent the data into the database.

· Database models are given as below:

(1)   Hierarchical Model

· It organizes data in an upside-down tree structure.

· There is a hierarchy of parent and child data segments.

· It uses Parent Child Relationships.

· Here root node is called parent node and root segment is called child node.

· The parent can have none, one or more child nodes but child nodes can not

have the multiple parent node.

· That’s why it represents data into one-to-many relationship between two

entities.

Advantages:

(1) Provide data sharing, data security and data integrity.

(2) Parent/child relationship provides data simplicity.

(3) Provide efficient 1-M relationship.

Disadvantages:

(1) Implementation Complexity.

(2) Lack of structural independence.

(2)   Network Model

· In Network model we can represent data other than one-to-many relationship.

· It can represent more than one parent per child.

· It represents data in many-to-many relationship.

· The basic data model in the network model is the set construct. A set consist a set

name and a record type.

Advantages:

(1) Conceptual simplicity.

(2) Freedom from problem of data access.

(3) Data Independence.

(4) It includes DDL, DML in DBMS.

Disadvantages:

(1) System complexity.

(2) Absence of structural independence.

(3)   Relational Model :

· It was developed by E.F. Codd.

· It uses simple tables instead of more complex tree and network structure.

· A relational database model is a collection of different tables.

· Here data and the relationships between the data are organized in tables.

· Some attributes in tables are defined as KEY attributes.

· A relation consists of a heading and a body. A heading is a set of attributes. A

body is a set of tuples.

· Properties of Relational Tables are given as below.

(1) Unique rows and columns.

(2) Key attributes.

(3) Relationship between attributes.

Advantages:

(1) Structural Independence.

(2) Conceptual simplicity.

(3) Freedom from problem of design, implementation and maintenance.

(4) Faster Query capabilities.

Disadvantages:

(1) Hardware/Software problems.

(2) Sometimes create problem in design.