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SDLC (III): System Analysis Process Modeling Using Data Flow Diagrams (I) (Chapter 6) Introduction to Structured Methodology - A methodology is a systematic approach for carrying out specific tasks  a collection of principles, practices, and procedures - Before 1970s, there was no formal methodology - Structured methodology was introduced in the late 1970s.  A collection of structured analysis, design and programming approaches  Structured analysis and design i) “Structured Analysis and System Specification” by DeMarco ii) “Structured System Analysis: Tools and Techniques” by Gane and Sarson iii) “Structured Design: Fundamentals of a Discipline of Computer Program and Systems Design” by Yourdon and Constantine - Focus on the process analysis - Moderns structured methodology 1

 “Modern Structured Analysis” by Yourdon System Analysis - System analysis refers to the ability to break down a whole system into its component parts so that its organizational structure may be better understood - Goal: to define the system’s requirements  Functional requirements  what the system is supposed to do - Input: User requirements - Output: system specifications (system models)  Two major system models are process model (e.g., Data Flow Diagram) and data model (e.g., Entity-Relationship Diagram) - Two mutually contradictory goals should be met  Clear and intelligent to the users  Complete and precise to designers - First point in a project in which you can get meaningful information about the project (in terms of cost, schedule and functionalities …) - When system analysis is done, you should know  What the users are going to get  When they get them 2

 How much it is going to cost

Data Flow Diagram (DFD) - DFD is one of the most widely used graphical

modeling languages for the structured system analysis. Using DFD, system analysts analyze and document the target system’s requirements. - DFD involves graphically representing the

processes that capture, manipulate, store, and distribute data between a system and environment and between components within a system - DFD depicts the movement of data between

external entities, the processes and data stores within a system - DFD enables you to model how data flow

through an information system, the relationships among the data flows, how data come to be stored at specific locations - DFD is an example of process model  Shows the processes that change or

transform data with an emphasis on the process logic underlying the system 3

- DFD is an example of logical model  Independent of implementation technology  Provides freedom from committing to the

implementation technology too early - DFD is an excellent communication tool - DFD is a modeling language  Notations  Syntax

Notations Used in DFD (Gane and Sarson) - There are many notation sets for DFD. One of

the most popular notation sets is Gane and Sarson’s. Another popular one is Yourdon’s notation set. We’ll use Gane and Sarson’s notation. - Four notations  External entity  Process  Data flow  Data store

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External Entity - An external entity is any one that provides data into the system or gets the data from the system  input provider (source of data) or output receiver (destination of data) - Can be a person, an organization or another information system - External to the system  external entities are outside of the system - Notation  square

Examples of external entities in Order MGMT System

Order Management System CUSTOMER

INVENTORY SYSTEM

MANAGEMENT ACCOUNTING DEPT.

5

- Label it with appropriate name-- use NOUN!  Accounting department  Customer  Student  Inventory system

Data Flow - Movement of data from one point to another - Data in motion - Notation  a line with an arrow Customer Information Payment

Sales report

- Label it with appropriate name-- use NOUN!

Process 6

- Essence of data flow diagram - A process receives inputs, transforms them and produces outputs.  Contains business rules (or business logics) that transform the data, and produce the required results  They are the works or actions performed on data - Notation  rectangle with rounded corner 1 Calculate order total

- Give a unique identifying number  The number doesn’t mean a sequence. It is a

simply unique reference number - Label it with appropriate name-- use VERB!  Calculate order total  Calculate gross pay  Print receipts  Validate customer information

(Examples) 7

4

hours worked

wage rate

Calculate Gross pay

6 Payment info

Print Receipt

receipt

gross pay

unitPrice

1

QtyOrdered

Calculate order total

- Data flow leaving a process is labeled differently from the one entering it

Customer info.

2

Customer info.

Validate Customer information

Wrong!

Customer info

2

Validated customer info.

Validate Customer information

Correct! Data Store 8

- Represents data that are stored in the system  Depository for data  Equivalent to a file in the file processing system; or a table in the database system - Notation  Open-ended rectangle with unique reference number (in the Gane and Sarson notations).  e.g., Customer data store will store customer information (such as customer number, name, address, phone number …) D1

Customer

 You can also use a short and wide rectangle as shown below. Either one will be acceptable. D1

Customer

- Label appropriate name -- use NOUN!  STUDENT, PRODUCT … D2

Student

D3

Product

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- Can be a manual store (e.g., file cabinet) Syntax of DFD See the Figure 6-7 on your textbook (Page 165) Rule 1. First rule in DFD is a process must have at least one input and output data flow. 1 xxxxxxx

Wrong! (X) 2 xxxxxxx

Wrong! (X)

3 xxxxxxx

Wrong! (X)

---------------------------------------------------------------1 xxxxxxx

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Correct! (O)

Rule 2. Rule 2 is that external entities and data stores cannot be connected each other directly.

A

B

Wrong! (X) 1 xxxxxxx

A

B

Correct! (O). You need a process between A and B.

---------------------------------------------------------------D1

xxxxx

D2

xxxxx

Wrong! (X)

A

D1

11

xxxxx

Wrong! (X)

You need a process between D1 and D2 and also a process between A and D1. Rule 3. A fork in DFD means exactly same data goes from a common location to multiple locations. 2

1

Fork A B 3

Wrong! (Two different data, A and B, are moving on one flow.)

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The following two DFD are correct ones. 2

A

1

A 3

Correct!

2

1

A

3

B

Correct! Two different data move on the different flows.

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Rule 4. A join in the DFD means exactly same data flow comes from multiple places to common location.

1

A Join

3

B 2

Wrong! (Two different data, A and B, are moving on one flow.)

14

1

A

3

A 2

Correct! 1

A

2

3

B

Correct!

Your textbook discusses the use of recursive relationships in DFD (named Rule M), which states a data flow cannot 15

go back directly to the same process it leaves. I think this rule is a little debatable. So ignore the rule. We are not going to apply this rule for our discussion.

Developing DFD - Key concept  “functional decomposition”  An iterative process of breaking a system

down into finer details  You decompose a complex whole system into smaller components until all the components become manageable chunks  Stepwise refinement  This can deal with “complexity due to size” problem well. If you are able to reduce the size, you can exponentially reduce the complexity. - Data flow diagram is an excellent tool for the

system’s decomposition. - DFD is a set of diagram in which one process on

a given diagram is explained in greater detail on the lower level diagram  Context Diagram  Level 0 Diagram  Lower level Diagram (Level 1, Level 2 …)

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- The first step in developing DFD is to draw

Context Data Flow Diagram.

Context DFD (Data Flow Diagram) - Highest level description of the target system  Provides an overview of the target system  Shows the system boundary, external entities

that interact with the system, and the major data flows between the external entities and the system  Shows how the system as a whole interacts with the external environment - Rule 1: There is a single process (only one

process) in the Context DFD.  The process represents the entire system  The unique reference number is 0 (zero).  Its name is the system’s name. Use a NOUN. A process is labeled with a VERB, but this is the only exception. - Rule 2: All external entities and major

input/output data flows are included in the Context DFD. - Rule 3: No data store is shown in the Context DFD. 17

Example: Context DFD for Order Management System Order Info

Product Info INVENTORY SYSTEM

CUSTOMER

Customer Info OrderDelivered

ACCOUNTING DEPT.

-

Payment

0 Order Management System

Sales Report

MANAGEMENT

Single process Reference number  0 (zero) Name  system’s name (labeled with Noun) All external entities Major input and output data flows No data store shown

Figure 6-5 on your textbook (p. 162) provides another example of Context DFD. 18

Practice Problems For your practice, I am placing three exercise problems. Based on the case descriptions, create a context DFD for each case. These exercises will take about 30 ~ 40 minutes. I have also placed solutions to the exercises at the end of this lecture. Be sure to finish the exercise first for yourself and then check your work with the solution.

Exercise 1 Customer Management System

Customer information is entered from customers. The system finds his/her information from the customer file (data store). If the customer is not an existing customer, then the system adds the new customer information to the file (data store). When the new customer information is added, the system assigns a new customer number. At the end of each day, the system prints the list of newly added customer to the customer representatives.

-

Create a Context DFD for the Customer Management System.

19

Exercise 2 Textbook Order Management System The purpose of the TEXTBOOK ORDER MANAGEMENT SYSTEM at a campus bookstore is to supply textbooks to students for classes at a local university. The university’s academic department submits to the bookstore initial data about courses, instructors, textbooks, and projected enrollment in a book master list. The bookstore generates a purchase order, which is sent to publishing companies supplying textbooks. Book orders arrive at the bookstore accompanied by a packing slip from the publishing companies. Students fill out a book request that includes course information. When they pay for their books, the students are given books and a sales receipt. Accounting department processes the payments received.

-

Create a Context DFD for the Textbook Order Management System.

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Exercise 3 Perfect Pizza Ordering System Perfect Pizza is a restaurant that sells pizza and Buffalo wings. The restaurant wants to install a system to record orders from customers. The following is the summary of the business activities at Perfect Pizza. The first module of the system is to validate the customer information. When regular customers call Perfect Pizza on the phone, they are asked their phone number. When the number is typed into a computer, the customer information (e.g., name, address, and last order date) is automatically brought up on the screen for verification from the CUSTOMER file. When the customer is new, his/ her information is added to the CUSTOMER file. The second module of the system is to process customer orders. The orders are taken from customers. The order information (e.g., item and quantity ordered) is entered into the program. Once an order is taken, the total amount is calculated. The unit price of the product ordered is retrieved from the PRODUCT file. The processed order information (including order date and total amount) are stored in the ORDER file. The order information is given to the cook. The cook prepares the products for delivery. Then a receipt is printed. The next process delivers the order to the customer. Occasionally, special offers (coupons) are printed from the COUPON file so the customer can get a discount for the next purchase. These coupons are given to customers together with the orders and receipts (if any). Another module is to produce weekly reports. Weekly totals are produced for the management review from the ORDER file. The performance statistics from the report is sent to the management and used for comparison with last year’s performance.

-

Create a Context DFD for the Perfect Pizza Ordering System.

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End of the Lecture Remember there are solutions to the exercises on the following pages.

Exercise 1 Solution Customer Management System Context DFD

0 Customer

Customer Info

Customer Management System

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New Customer List

Representative

Exercise 2 Solution Textbook Inventory System Context DFD

Academic Department

book master list

0 Textbook Inventory System

purchase order

Publishing Company

book ordered packing slip

payment received payment book book request receipt

Accounting Department

Students

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Exercise 3 Solution Pizza Order System Context DFD

0 order info phone number

Pizza Order System

customer order info

product

performance report

new customer info

CUSTOMER

MANAGEMENT

delivery (order, coupon, receipt)

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COOK...