 Important Computer Awareness for IBPS Exams 2017 (Day-10) – DBMS Part-10:
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Database Management Systems (DBMS) – PART 10
Continuation of part-9 is given below: Click Here to view Part-9
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2.Physical Data Models:
Physical data model
represents how the model will be built in the database. A physical database
model shows all table structures, including column name, column data type,
column constraints, primary key, foreign key, and relationships between tables.
Features of a physical data model include:
represents how the model will be built in the database. A physical database
model shows all table structures, including column name, column data type,
column constraints, primary key, foreign key, and relationships between tables.
Features of a physical data model include:
Specification all
tables and columns.
tables and columns.
·        Foreign keys are used to identify relationships between tables.
·        Denormalization may occur based on user requirements.
·        Physical considerations may cause the physical data model to be quite different from the logical data model.
·        Physical data model will be different for different RDBMS. For example, data type for a column may be different between MySQL and SQL Server.
3. Record based data models:
(a) Hierarchical data models:
A hierarchical
database model is a data model in which the data is
organized into a tree-like structure.
The data is stored as records which
are connected to one another through links. A record is a collection of fields, with each field
containing only one value. The entity
type of a record defines which fields the record contains.
database model is a data model in which the data is
organized into a tree-like structure.
The data is stored as records which
are connected to one another through links. A record is a collection of fields, with each field
containing only one value. The entity
type of a record defines which fields the record contains.
(b) Network Data Models:
The network
model is a database
model conceived as a flexible way of representing
objects and their relationships. Its distinguishing feature is that the schema,
viewed as a graph in which object types are nodes and relationship types are
arcs, is not restricted to being a hierarchy or lattice.
model is a database
model conceived as a flexible way of representing
objects and their relationships. Its distinguishing feature is that the schema,
viewed as a graph in which object types are nodes and relationship types are
arcs, is not restricted to being a hierarchy or lattice.
The Network model replaces the hierarchical tree with a graph
thus allowing more general connections among the nodes. The main difference of
the network model from the hierarchical model, is its ability to handle many to
many (N:N) relations. In other words, it allows a record to have more than one
parent.
thus allowing more general connections among the nodes. The main difference of
the network model from the hierarchical model, is its ability to handle many to
many (N:N) relations. In other words, it allows a record to have more than one
parent.
(c) Relational Data Models:
 Where all data is represented in terms of tuples,
grouped into relations. A database organized in terms of the relational
model is a relational database.
grouped into relations. A database organized in terms of the relational
model is a relational database.
The purpose of the relational model is to provide a declarative method for
specifying data and queries: users directly state what information the database
contains and what information they want from it, and let the database
management system software take care of describing data structures for storing
the data and retrieval procedures for answering queries.
specifying data and queries: users directly state what information the database
contains and what information they want from it, and let the database
management system software take care of describing data structures for storing
the data and retrieval procedures for answering queries.
ONE LINER:
1. In which model data is stored
in computer memory?
in computer memory?
   Physical Data Model
2. In which Data model parent can
have n- children?
have n- children?
   Hierarchical data model
3. One to many is for:
   Hierarchical data model
4. Which is designed to address
the drawbacks of hierarchical model?
the drawbacks of hierarchical model?
    Network data model
5. Tables, relations, keys,
attributes are established in:
attributes are established in:
   Relational data model
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