DBMS Unit-2

Data Model
Gives and idea of how the final system or software will look after and the development is completed This concept is exactly like real world modeling in which before constructing any project (Buildings, Bridges, Towers) engineers create a model for it and gives the idea of how a project will look like after construction A data model is an overview of a software system which describes how data can be represented and accessed from software system after its complete implementation Data models define data elements and relationships among various data elements for a specified system A data model is a way of finding tool for both business and IT professionals which uses a set of symbols and text to precisely explain a subset of real information to improve communication within the organisation and thereby lead to more flexible and stable application environment Data model is a simple abstraction of complex real world data gathering environment
Importance Of Data Models In DBMS

A data model is a set of concepts that can be used to describe the structure of data in a database Data models are used to support the development of information systems by providing the definition and format of data to be involved in future system Data model is acting like a guideline for development also gives an idea about possible alternatives to achieve targeted solution A data model can sometimes be referred to as data structure especially in the context of programming languages
Advantages Of Data Model

Data model prevents the system from future risk and failure by defining structure of data in advance As we got an idea of final system at the beginning of development itself so we can reduce the cost of project by proper planning and cost estimation as actual system is not yet developed Data repetition and data type compatibility can be checked and removed with help of data model We can improve Graphical User Interface (GUI) of system by making its model and get it approved by its future user so it will be simple for them to operate system and make entire system effective
Basic Building Block

The basic building block for any of the model is entities, attributes, relationships and constraints ENTITY A fundamental component of a model which has its own independent existence in real world. E.g. A Student, Faculty, Subject. An entity can be an object with physical existence or it may have logical existence. Entities like department, section, adults may have physical or logical existence
Basic Building Block Contd

ATTRIBUTES
Each entity has its own properties which describes that entity, such properties are called as attributes A particular entity will have some value for each of its attributes EXAMPLE Employee entity may be described by attributes name, age, phone etc.
RELATIONSHIPS
It is an association among several entities for e. g. Employee works for Department. The degree of the relationship is the number of participating entity types in a particular relation Data model uses three types of relationships
Types Of Relationships
One is to one One entity is associated with at most one other entity. E.g. One department can have only one manager One is to Many One entity is associated with any number of entities in other entity. E.g. One teacher may teach to many students Many is to Many One entity is associated with any number of entities in other entity. E.g. Books in library issued by students
Business Rules
Database designer needs to take help from concepts such as entity, attributes and relationships to build a data model, but the above things are not sufficient to describe a system completely Business rules may define actors and prescribe how they should behave by setting constraints and help to manage business change in the system Business rules are statements of a discrete operational business policy or practice within specific organisations that constrains the business. It is intended to control or influence the behavior of the business
Characteristics Of Business Rules

Atomicity Rule should define any one aspect of the system environment. E.g. College should have students in it. Business Format Rule should be expressed in business terms understandable to business people. E.g. ER diagrams, Object diagrams etc. Business Commonality Each rule should confirm business scope. E.g. College system must define characteristics in college database
Characteristics Of Business Rules Contd

Business Ownership Each rule is governed by a business person who is responsible for verifying it, enforcing it and monitoring need for change. E.g. End user or customer is responsible for requirements submitted by him Classification Each rule can be classified by its data and constraints Business Formalism Each rule an be implemented in the related information system. Business rules should be consistent and non-redundant EXAMPLES
A student may take admission to college One subject is taught by only one professor A class consists of minimum 60 and maximum 80 students
Types Of Business Rules

DEFINITIONS Define some business terms. Definitions are incorporated in systems data dictionary. E.g. A professor is someone who teaches to students FACTS Connect business terms in ways that make business sense. Facts are implemented as relationships between various data entities E.g. A professor may have student
Types Of Business Rules Contd

CONSTRAINTS Shows how business rules shows how business terms are connected with each other. Constraints usually state how many of one data entity can be related to another data entity E.g. Each professor may teach up to four subjects DERIVATIONS Enable new knowledge or actions. Derivations are often implemented as formulas and triggers. E.g. A student pending fees is his fees paid minus total fees
Method Of Defining Business Rules

Define the scope of your analysis State the objectives of the defined scope Identify the actors within the defined scope Uncover business confusions Create one or more use cases Identify system decisions
Hierarchical Model
First DBMS model Data sorted hierarchically in top down or bottom up approach Uses pointers to navigate between stored data Represents data as a hierarchical tree One parent node can have many child nodes but one child cannot have more than one parent. EXAMPLE Information Management System (IMS) from IBM
Hierarchical Model Contd

CEO
PM
PM
PrM
PrM
PrM
PL
PL
PL
PL
TL
TL
TL
TL
Developer
Developer
Developer
Developer
Advantages Of Hierarchical Model

Conceptual Simplicity
Relationships between various levels is logically very simple. Hence database structure becomes easier to view
Database Security
Security is given by DBMS itself it does not depends on programmer has given security or not
Simple Creation, Updation And Access

It is simple to construct with the help of pointers. Adding and deleting records is easier . Faster and easy data retrieval
Database Integrity
There is always parent child relation between different levels and hence child records are attached with parent records which maintains data integrity
Data Independence
Itself maintains data independence thus reducing program efforts and its maintenance that is id one part of the code is changed no need to change the other part
Efficiency
Good performance when database contains large amount of data in which one record has many related records
Disadvantages Of Hierarchical Model

Complex implementation
Only data independence is not enough for designer and programmers to build database system they need to have knowledge of physical data storage which may be complex
Difficult to manage
Any change in location of data needs change in all application programs that accesses changed data. Data access is restricted by pointer path
Lack of structural independence

Change in database structure affects data access
Complex application programming

Programmers must know how data is stored and path of data storage
Limitations in implementation
1:N relationship can be implemented but implementing M:N relationship is difficult
Network Model
Uses pointers but without the need of parent child relationships Used in network databases Relationship between any two record types is called as SET A relationship can be 1:N or M:N EXAMPLE IDS(Integrated Data Store) one of the products based on network models developed by IBM and North American Rockwell
Network Model Contd

A
Advantages Of Network Model

Simple Design
Is simple and easy to design and understand
Ability to handle many types of relationship

Can handle one-to-many or many-to-many or other relationships and hence manages multi user environment
Ease of data access

An application can access a parent record and all the member records within a set
Data Independence
Application programs work independently of the data. Any changes made in data do not effect the application program
Conformance to standards
Facilitates the administrators portability by offering data creation by DDL and DML
Disadvantages Of Network Model

System Complexity
Data are accessed one record at a time hence the complexity for the system increases for accessing multiple records at a time
Lack Of Structural Independence

Any changes made to the database structure or data require the application programs to be modified before it can access data
Relational Model
Proposed by E. F. Codd An attempt to simplify database structure by making use of tables and columns Collection of 2-dimensional tables which consists of rows and columns Tables are known as relations columns are known as attributes and rows are known as tuples Uses collection of tables to represent relationships amongst data Each database item is viewed as a record with attributes. A record with similar attributes is called as table. Each table contains a record of particular type The database uses relational model called as RDBMS (Relational Database Management System)
Relational Model Contd.

COLUMNS
ROWS
VALUE
TABLE
Advantages Of Relational Model

Relational Algebra
Supports relational algebra, union, intersection, difference, Cartesian product, select, project, join and division
Dynamic View
View is not a part of physical schema, hence changing data in he table also changes the data present in the view
SQL
English like language which can be used to access data form RDBMS. Most vendors support SQL
Excellent Data Security

Support the concept of user rights thus meeting the needs of databases
Performance
Performance and support to new hardware technologies and flexible for all types of data needs
Scalability
Scalable and provide good support for the implementation of distributed systems and other advanced database systems
Entity Relationship Model

Defines data elements and relationships among various data elements for a specified system Based on the perception of real world data that consists of set of entities (data items) and relationships among these entities Popular high level conceptual model used for conceptual design of database An entity is a fundamental component of ER model which is a thing in real world with its own independent existence. Example Student, Department etc. Attributes are properties that describe the entities and its values become a major part of data stored in database A particular entity will have some value for each of its attributes Relationship is an association among several entities and is illustrated by diamond and read from left to right
Entity Relationship Model Contd

DEPTNO EMPNO EMPNAME
DEPARTMENT
CONTAINS
EMPLOYEES
DEPTNAME LOCATION EMPSAL
EMPAGE
Advantages Of ER Model
Very Simple Design
Simple and easy to design logical view of data
Ease Of Representation
Designer, programmer, developer can understand system very easily by looking at an ER model constructed
Integrated With Relational Databases

Completely integrated with relational model which can offer well structured design process
Disadvantages Of ER Model
Limited Constraint Representation
Model can display those constraint that are directly tied by relationships but not possible to represent some constraints like average marks etc.
No DML
Do not have any language by which we can insert data in database
Loss Of Information Content

Does not deal with actual data values so it may not be possible to represent information content of system
Object Model
Data is stored in the form of objects which are structures called classes that display the data within it Fields are instances of these classes called objects Used in File Management System DBMS developed is called OODBMS (Object Oriented Database Management System) OOD can handle complex applications such as scientific experiments, geographical information system etc Draws its concept from real world objects which deals with data at higher level that is with the objects surrounding the data Represents database in terms of objects, attributes and their behaviors
Object Model Contd
Advantages And Disadvantages Of Object Model

Advantages
OO features provide a clear modular structure which is good for designing abstract data types where internal implementation details are hidden Easy to maintain and modify existing code as we can create new model with small change in existing
Disadvantages
Often provided through object oriented languages such as C++ and Java Practically very complex and inapplicable many times

DBMS Unit-2

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Data Model

Importance Of Data Models In DBMS

Advantages Of Data Model

Basic Building Block

Basic Building Block Contd

Characteristics Of Business Rules

Characteristics Of Business Rules Contd

Types Of Business Rules

Types Of Business Rules Contd

Method Of Defining Business Rules

Hierarchical Model Contd

Advantages Of Hierarchical Model

Simple Creation, Updation And Access

Disadvantages Of Hierarchical Model

Lack of structural independence

Complex application programming

Network Model Contd

Advantages Of Network Model

Ability to handle many types of relationship

Ease of data access

Disadvantages Of Network Model

Lack Of Structural Independence

Relational Model Contd.

Advantages Of Relational Model

Excellent Data Security

Entity Relationship Model

Entity Relationship Model Contd

DEPTNAME LOCATION EMPSAL

Integrated With Relational Databases

Loss Of Information Content

Object Model Contd

Advantages And Disadvantages Of Object Model

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