DBMS Notes

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Database Management System

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Data Modeling

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Database Architecture

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Relational Model

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Relational Algebra

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Entity Relationship Model

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Functional Dependencies

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Normalization

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Transaction And Concurrency Control

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Deadlock

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Files and Storage

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Indexing

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Q

1

What are data models?

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Ans

Data model is representation of
1)Things (or entities or objects) of importance to a business or a system
2) How the things relate to each other
It is built and modified until it represents the structure well enough to write a system

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Q

2

What are the different database models?

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Ans

There are three types of data models:

1) Object Based Logical Models:
These models can be used in describing the data at the logical and view levels.
These models are having flexible structuring capabilities classified into following types.
a) The entity-relationship model.
b) The object-oriented model.
c) The semantic data model.
d) The functional data model.

2.Record Based Logical Models:
These models can also be used in describing the data at the logical and view levels.
These models can be classified into:
a. Relational model.
b. Network model.
c. Hierarchal model.

3. Physical Models:
These models can be used in describing the data at the lowest level( physical level).
These models can be classified into
a. Unifying model
b. Frame memory model.

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Q

3

Explain object relational database model?

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Ans

Object relational database model consist of classes, objects, inheritence etc. It is a combination of relational and object oriented database system.
It allows its users to inherit objects, tables etc. Complex data types can be formed using existing data types in this type of models. Sometimes it is difficult to handle these types types of databses as they are very complex.
These models are having flexible structuring capabilities classified into following types.
a) The entity-relationship model.
b) The object-oriented model.
c) The semantic data model.
d) The functional data model.

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Q

4

What is logical and physical designing process?

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Ans

PHYSICAL DESIGNING:
Physical database design is the process of choosing specific storage structures and access paths for the database files to achieve good performance for the various database applications. This step involves building indexes on some tables and clustering some tables.
The physical database design can have the following options.
1.Response Time:
This is the elapsed time between submitting a database transaction for execution and receiving a response.
2.Space Utilization:
This is the amount of storage space used by the database files and their access path structures on disk including indexes and other access paths.
3.Transaction Throughput:
This is the average number of transactions that can be processed per minute.

LOGICAL DESIGNING:
Under this, we must choose a DBMS to implement our database design and convert the conceptual database design into a database schema.
The choice of DBMS is governed by number of factors as below.
1.Economic Factor:
Economic factors consists software acquisition cost, maintenance cost, hardware cost etc.
2.Organizational Factors
Organizational factors consists of data complexity, sharing among applications, dynamically growing data etc.

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Q

5

Explain Hierarchical Model with example.

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Ans

Hierarchical databse model is the earliest database model. It looks like a tree data structure, a upside down tree. Data are related as parent child relationships i.e p parent have many childrens but a child can have only one parent. This model structure allows the one-to-one and a one-to-many relationship between two or various types of data. This structure use physical order of data records in storage. The hierarchal model is not flexible because adding new relationships can result in wholesale changes to the existing structure, which in turn means all existing applications need to change as well.
ADVANTAGES:
1. Promotes data sharing
2.Promote data integrity.
3. Efficient with one to many relationships

DISADVANTAGES:
1. Navigation takes time
2. Change in structure changes all application programs.
3. Implemetation is difficult
4.Lacks structural independence

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Q

6

Explain Network Model with example.

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Ans

In network model data is organised like graph structure. Unlike hierarchical database it can have more than one parent. The network model differs from the relational model in that data are represented by collections of records, and relationships among data are represented by links. This database model was used to map many-to-many data relationships. There can be more than one path from previous node to next node. The operations of the network model are maintained by indexing structure of linked list (circular) where a program maintains a current position and navigates from one record to another by following the relationships in which the record participates.
ADVANTAGES:
1. Data access if flexibal
2.Represents complex data better than hierarchical model.
DISADVANTAGES:
1.Complex implementation
2.Complex application programming.

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Q

7

Explain Entity Relationship Model with example.

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Ans

The entity-relationship data model perceives the real world as consisting of basic objects, called entities and relationships among these objects. It was developed to facilitate data base design by allowing specification of an enterprise schema which represents the overall logical structure of a data base.
Main features of ER-MODEL:
1.Entity relationship model is a high level conceptual model
2.It allows us to describe the data involved in a real world enterprise in terms of objects and their relationships.
3. It is widely used to develop an initial design of a database
4.It provides a set of useful concepts that make it convenient for a developer to move from a baseid set of information to a detailed and description of information that can be easily implemented in a database system
5.It describes data as a collection of entities, relationships and attributes.

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Q

8

Explain Relational Database Model with example.

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Ans

A relational database is a collection of one or more ‘relations’, where each relation is a table with rows and columns.
This is the primary data model for commercial data processing applications.
The major advantages of the relational model over the older data models are,
1.It is simple and elegant.
2.simple data representation.
3.The ease with which even complex queries can be expressed.
It concerned with three aspects of data:
1. Data structure ( tables)
2. Data integrity ( primary key rule, foreign key rule)
3. Data manipulation (Relational Operators):
Relational Algebra
Relational Calculus

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