Data Model means to model the data i.e., to give a shape to the data - to give a figure to the stored data.A data model makes it easier to understand the meaning of the data by its figure and thus we model data to ensure that we understand:
- The nature of the data itself,independent of its physical representations.
- Each users view to the relation of data.
- The use of data across application areas.
In simple words we can define data model as " A collection of high - level data description that hide many low - level storage details"."A data model can also be defined as a collection of conceptual tools for describing data,data relationships,data semantics and consistency constraints".Thus,A DBMS allows a user to define the stored data in terms of data model.
THE DATA MODELS ARE DIVIDED INTO THE THREE DIFFERENT GROUPS:
(a) Object - Based Logical Models
(b) Record - Based Logical Models
(c) Physical Models.
RECORD - BASED LOGICAL MODEL
Record-Based Logical Models describes data at Logical and View levels. When compared with object-based data models, the record-based logical models specifies the overall logical structure of the database and provides higher-level implementation.
Record - based models are so named because the data is kept in the form of records (documents) of several types, each record has fixed number of (fields or) attributes and each field is of fixed length.
The Record-Based Models are of three types
The relational model represents both data (entities) and relationships among data in the form of tables. Each table has multiple columns and each column has a unique name. Consider the following relational model :
The description of data in terms of tables is called as relations, from the above CUSTOMER and Account relations, we can make a condition that customer details are maintained in CUSTOMER relation database and their deposit details are maintained in Account relation database.
Network Model
Data in the network model are represented by collection of records and relationships among data are connected by links. The links can be viewed as pointers. The records in the database are represented in the form of graphs.
Hierarchical Model
Hierarchical Model is same as the Network Model i.e., Data in the Hierarchical Model also are, represented by collection of records and relationship among data are connected by links. The links can be viewed as pointers. But, the difference from Network Model is that, the records in the database are represented in the form of trees.
RECORD - BASED LOGICAL MODEL
Record-Based Logical Models describes data at Logical and View levels. When compared with object-based data models, the record-based logical models specifies the overall logical structure of the database and provides higher-level implementation.
Record - based models are so named because the data is kept in the form of records (documents) of several types, each record has fixed number of (fields or) attributes and each field is of fixed length.
The Record-Based Models are of three types
- Relation Model
- Network Model
- Hierarchical Model
The relational model represents both data (entities) and relationships among data in the form of tables. Each table has multiple columns and each column has a unique name. Consider the following relational model :
The description of data in terms of tables is called as relations, from the above CUSTOMER and Account relations, we can make a condition that customer details are maintained in CUSTOMER relation database and their deposit details are maintained in Account relation database.
Network Model
Data in the network model are represented by collection of records and relationships among data are connected by links. The links can be viewed as pointers. The records in the database are represented in the form of graphs.
Hierarchical Model
Hierarchical Model is same as the Network Model i.e., Data in the Hierarchical Model also are, represented by collection of records and relationship among data are connected by links. The links can be viewed as pointers. But, the difference from Network Model is that, the records in the database are represented in the form of trees.
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