indira gandhi national open university presents. a video lecture course: systems analysis
TRANSCRIPT
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Indira Gandhi
National Open University
presents
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A Video Lecture
Course:Systems Analysis
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DATA MODELING
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MODEL
A Model is an abstraction of something for the purpose of understanding it before building it.
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DATA MODELING
• Answers a set of following specific questions that are relevant to any data processing application
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Questions answered by a Data Model
• What are the primary data objects to be processed by the system
• What is the composition of each data object and what attributes describe the object
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• Where do objects currently reside
• What are the relationships between each object and other objects
• What is the relationship between the objects and the processes that transform them
Questions answered by a Data Model
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• To answer those questions,Data modeling makes use of Entity-Relationship Diagram(ERD)
• ERD enables a Software Engineer to identify data objects and their relationships using a graphical notation
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DATA OBJECTS
A data object is a representation of almost any composite information that must be understood by software.By composite information,we mean something that has a number of different properties or attributes.
A person is a data object
A car is a data object
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KeyOne or more attributes which uniquely identify a data object
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Attributes of Person: Name,Address,Age, Driving license number
Driving license number is the key
Attributes of Car: Make,Model,Chassis Number, Body type,Color
Chassis Number is the key
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RELATIONSHIPS
Data objects are connected to one another in a variety of different ways
Here, owns is the relationship
Example: a Person owns a Car
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Identification of Objects, Attributes & Relationships
Problem:
A University should schedule its class rooms for final Exams. Examinations will be conducted for all courses for students of all sections
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• Course
• Section
• Room
Data Objects
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• Name
• Department
• Code
Attributes of Course
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• S-number
• Enrollment
Attributes of Section
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• R-number
• Capacity
• Building
Attributes of Room
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Relationships:
• Code & S-number
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Entity Relationship Model
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Simple and Composite Attributes
• CITY is a Simple attribute
• NAME is a Composite attribute because we can subdivide it into First Name,Middle Name and Last Name
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Single and Multi Valued Attributes
• AGE is a single valued attribute
• DEPENDENT-NAME is a multi valued attribute
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Derived Attributes
• EMPLOYEMENT-LENGTH of Employee entity set is a derived attribute of Start-date and Current-date
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Keys
•Super Key
•Candidate Key
For example,Consider CUSTOMER entity set with attributes (1)Social security (2)Customer name (3)Customer street (4)Customer city
Now,Social security is a super key.Also,any set of attributes containing Social security forms a super key
So,Social-security is also candidate key
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ENTITY-RELATIONSHIP DIAGRAMA E-R diagram consists of following components:
• Rectangles-represent Entity sets
• Ellipses-represent Attributes
• Diamonds-represent Relationship sets
• Lines-link attributes to Entity sets and Entity sets to relationship sets
• Double Ellipses-represent multi valued attributes
• Dashed Ellipses-denote derived attributes
• Double lines-indicate total participation of an entity in a relationship set
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E-R diagram corresponding to Customers and Loans
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RELATIONSHIPS BETWEEN ENTITY SETS
• One to Many
• Many to One
• One to One
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RELATIONSHIP SETSSo,Attributes of Borrower :Social Security, Loan-number
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WEAK ENTITY SETS
For example, an entity set with attributes Name,Age,Height is a Weak Entity Set
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STRONG ENTITY SET
• An Entity set with Passport no.,Name ,age,Height,Address is a Strong Entity Set as Passport no. can be used as key attribute
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Summary
• Definition of Modeling
• Questions answered by Data Modeling
• Definitions of Data Object,Attributes and Relationships
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Summary(contd.)
• Analyzing a given problem and finding Data Objects, Attributes and Relationships between objects of that problem
• Introduction to Entity – Relationship Modelling
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Summary(Contd.)
• Simple and Composite Attributes
• Single and Multivalued Attributes
• Derived Attributes
• Candidate Keys
• Entity-Relationship Diagram
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Summary(contd.)
• Weak Entity Sets
• Strong Entity Sets