Data Flow Diagrams

Data Flow Diagrams
DFD
Meaning/Type
Introduced by De Marco (1978) and Gane and Sarson (1979) DF is a graphic representation of a system. Physical and logical
Levels
E TLP E 1 2 3
3.1 1.1 1.2 1.3
3.2
1.1.1
1.1.2
1.1.3
Symbols
Flow
Entity
Process
Data Store
Prepare Physical and Logical DFD

Issue out a book from library
Library User 1.0 Issue Clerk Selected Book + Lib Card 1.0 Book Issue Process
Book issued after Stamping and recording The return date
Lib Card Store

Return to Library
Library User 2.0 Receiving Clerk 2.0 Book Receiving Process
Book
Return the Lib card
Lib Card Store

Return to Library
Library User 2.0 Book Receiving Process
Book
Fine slip
2.1 Check for Over due Process Fine File
Return the Lib card Fine Money Lib Card Store
Home Assignment
Getting ticket reserved for a train journey Getting item issued form a store Getting your mark sheet from a University Office
Home Assignment
A magazine is published monthly and is sent by post to its subscribers. Two months before the expiry of subscription, a reminder is sent too the subscribers. If subscription is not received within a month time another reminder is sent. If renewal subscription is not received up to two weeks before of the expiry of the subscription the subscribers name is removed from the mailing list and the subscriber is informed. Draw a logical DFD.
Answer
Second Example
A customer presents a cheque to a clerk. The clerk checks a file containing all account numbers and makes sure whether the account number in the cheque is valid., whether adequate balance is there in the account to pay the cheque, and whether signature is authentic. Having done these the clerk gives the customer a token. The clerk also debits customers account by the amount specified on the cheque. If cash cannot be paid due to error in the cheque, the cheque is returned. The token number is written on the top of the cheque and it is passed on to the cashier. The caisher calls out the token number and the customer goes to the cash counter with the token. The cashier checks the token number, takes the customers signature ,pays cash, enters cash paid in a ledger called day book and files the cheque.
Physical DFD of encashing cheque
For Logical Identify Major Process

Retrieve customer record Check balance update and issue token Store token number and cheques Search and match token Update daily cash book
Logical DFD
Entity Relation and Attributes

Entity which specify distinct real world items in an application. Relationships which connect entities and represent meaningful dependencies between them Attributes which specify properties of entities and relationships
ER Representation
Vendors Orders
Supplies
Placed With
Items
Vendors
ER Representation
Orders
Placed For
Orders Paced with Vendors Vendors Supplies Items Orders Place for Items
Placed With
Vendors Items Supplies
ER Representation
Vendors Orders
Supplies
Placed With
Items
Vendors
Attributes
Vendors
Vendor Code Vendor Name Address
Supplies
Vendor Code Item Code Order No Quantity Supplied Date of Supply Price/Unit Item Code Item Name
Items
Relations
Teacher
Vendor
Advices
Supplies
N Students
M Items
Breaking the Entities

First normal form: A table is in the first normal form if it contains no repeating columns. Second normal form: A table is in the second normal form if it is in the first normal form and contains only columns that are dependent on the whole (primary) key. Third normal form: A table is in the third normal form if it is in the second normal form and contains only columns that are non dependent on the primary key.
Order Table
Order no. Order Date Item Lines Item code 1456 1886 09/09/2011 04/03/2012 3687 Qty Price /unit 52 50.40
4627
4623 2345 4589 1788 19/05/2000 9876
38
44 33 55 44
60.20
20.25 19.89 44.33 12.89
Order Table IN First Normal Form

Order no. Order Date Item Lines Item code 1456 1456 09/09/2011 09/09/2011 3687 4627
Qty Price /unit

52 38 50.40 60.20
1886 1886
1886 1788
04/03/2012 04/03/2012
04/03/2012 19/05/2000
4623 2345
4589 9876
44 33
55 44
20.25 19.89
44.33 12.89
Order Table IN First Normal Form

Order no. Order Date Item Lines Item code 1456 1456 09/09/2011 09/09/2011 3687 4627
Qty Price /unit

52 38 50.40 60.20
1886 1886
1886 1788
04/03/2012 04/03/2012
04/03/2012 19/05/2000
4623 2345
4589 9876
44 33
55 44
20.25 19.89
44.33 12.89
Order Table IN Second Normal Form

Second normal form: A table is in the second normal form if it is in the first normal form and contains only columns that are dependent on the whole (primary) key. (a) Orders = Order no. + Order Date (b) Order Details = Order no. + Item Code + Qty (c) Prices = Item Code + Price /Unit
Order Table IN Third Normal Form

Third normal form: A table is in the third normal form if it is in the second normal form and contains only columns that are non dependent on the primary key. (a) Orders = Order no. + Order Date (b) Order Details = Order no. + Item Code + Qty + Price/Unit
(a) Item Master = Item Code + Price/Unit
Practice
Raw Employee Table
Employ Employ Job Job ee ee code Title Number Name
Project Completi Hours Numbe on Work r Date ed
Raw Employee Table

Employ Employ Job Job ee ee code Title Number Name 120 Ramu 1 Pgm 120 121 121 270 270 Ramu Damu Damu Daku Daku 1 1 1 2 2 Pgm Pgm Pgm Analys t Analys t Project Completi Hours on Numbe Work r Date ed 01 7/17 37 08 01 12 08 12 1/12 7/17 3/21 1/12 3/21 12 45 107 10 41
Raw Employee Table

Employ Employ Job Job ee ee code Title Number Name 279 Shiftu 1 Pgm 279 279 Shiftu Shiftu 1 1 Pgm Pgm Project Completi Hours on Numbe Work r Date ed 01 1/12 27 08 12 3/21 7/17 20 51
Primary Key : Employee Number , Project Number
First Normal Form

Relational tables are automatically in first normal form. A table in first normal form may contain highly redundant data resulting in the following serious problems. Insert : A new project can not be entered until there are employees working on it. Delete : Suppose a employee working only on one project stops working . Then deleting the record of the employee will also delete other information if the project also Updating : Suppose an employee changes his job form Programmer to Designer . This updating
Second Normal Form

Identify the primary key and determine which columns are functionally dependent on it. Employe Employe Job e e Code Number Name Projec Completi t on Numb Date er Job Title
Employee Project Number Number
Hours Worked
Third Normal Form

Remove Transitive Dependency ie ?A- B C If C is functionally depends in B and B depends on A then C depends in A Job Job Job Emp Employe Employe Job Code Title e e Code Number Name
Project
Projec Completi t on Numb Date er
Employee Project Number Number

Hr Worked
Hours Worked

Data Flow Diagrams

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Data Flow Diagrams

3.1 1.1 1.2 1.3

Prepare Physical and Logical DFD

Book issued after Stamping and recording The return date

Lib Card Store

Prepare Physical and Logical DFD

Return the Lib card

Lib Card Store

Prepare Physical and Logical DFD

2.1 Check for Over due Process Fine File

Return the Lib card Fine Money Lib Card Store

Physical DFD of encashing cheque

For Logical Identify Major Process

Entity Relation and Attributes

Vendors Items Supplies

Breaking the Entities

Order Table IN First Normal Form

Qty Price /unit

Order Table IN First Normal Form

Qty Price /unit

Order Table IN Second Normal Form

Order Table IN Third Normal Form

(a) Item Master = Item Code + Price/Unit

Raw Employee Table

Employ Employ Job Job ee ee code Title Number Name

Project Completi Hours Numbe on Work r Date ed

Raw Employee Table

Raw Employee Table

Primary Key : Employee Number , Project Number

First Normal Form

Second Normal Form

Employee Project Number Number

Third Normal Form

Projec Completi t on Numb Date er

Employee Project Number Number

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