Data model is a mechanism that provides data abstraction for database application. data modelling is used for representing entities of interest and their relationship in the database. data model of collection of conceptual tools for describing data, data relationship and attachment 1 and data constraints.
They are different data models of database:
Object based logical model
1. Entity relationship model
2 object oriented model
3 semantic data models
Record based logical model
1. relational model
2 network model
3 hierarchical model
Hierarchical data model
HDM uses the tree concept to represent data and relationship among data. the Lords of the tree are connected by pointer all links. the relationship between the entities represented by the structure of the resulting ordered tree. is one parent and 30 one or more child. the parent record type can have any number of children record type. every child node a single parent node. to record types in hierarchy tree at most one relationship between them and his relationship is that of one two one or one to many
Limitation of Hierarchical Data Model
1 Each hierarchical tree can have only one root record type and this record type doesn’t have a parent record type.
2. the root can have any number of child record types, each of which of can itself be a root of hierarchical tree.
3. which skeleton record type can have only one panel record type does a many-to-many relationship cannot be directly expressed between two record types.
4. deleting the record occurrence require Hollywood children record of currencies.
5.Each Child Record Type can have only one parent record type ,thus many to many relationships can not be directly expressed between two records
Network data model
To overcome the problems posed by hierarchical model the network data model is developed. which allows multiple parent child relationship. these relationships are known as sets In Network data model .IN network data model data are represented by collection of records and relationships among data are represent by Link. this model support one to many and many to many relationships.
Relational data model
relational data model is the most widely used data model, the vast majority of current database system are based on relational model. relational model uses a collection of tables to represent both data and the relationship among those data. relational model is an example of record based model. which record type defines a fixed number of fields at the columns of the table corresponding to the attribute of the record type.
Object relational data model
the database management system similar to a relational database but with an object oriented database model, objects classes and inheritance supported in database schemas and in the query language. ladies and it supports extension of data model with custom data types and methods
The Entity relationship model
The Entity relationship data model is widely widely used data model and it provides a convenient graphical representation you data relationships and constraints. it consist of basic objects called entities and a relationships among these entities entity is nothing but an object.
each entities are described in a database by set of attributes. and a relationship is an association among several entities.
ER diagram are used to represent logical structure of database graphically. it contain following components
Rectangles– It represents entity sets
Ellipses– it represents attributes
Diamonds– it represents relationship among entity sets
Lines -which link attributes to entity sets and entity sets to a relationships.
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