IS421 07 Class Lecture

Learning Objectives Understand the logical modeling of processes through studying data flow diagrams  How to draw data flow diagrams using rules and guidelines  How to decompose data

Information Systems System Analysis 421 Class Seven

Structuring System Requirements:

Process Modeling

Learning Objectives

 Understand the logical modeling of processes through studying data flow diagrams

 How to draw data flow diagrams using rules and guidelines

 How to decompose data flow diagrams into lower-level diagrams

 Balancing of data flow diagrams

8.2

Learning Objectives

 Explain the differences among four types of DFDs:

current physical, current logical, new physical and new logical

 Discuss the use of data flow diagrams as analysis tools

 Compare and contrast data flow diagrams with Oracle’s process modeling tool and with functional hierarchy

diagrams

 Discuss process modeling for Internet applications

8.3

Data Modeling

Entity Relationship

Prototypes Data Flow

Diagram

– Built to understand the existing system as a way to

document business requirements

– Data modeling is a technique for defining business

requirements

• Data is viewed as a resource to be shared by as many processes as possible, data must be organized in a way that is flexible and adaptable to unanticipated business requirements

System Modeling

• Physical model shows not only what a system does but how the system is physically and technically implemented -

depicts technical design

• Logical models depict business requirements illustrates the essence of the system

– Move biases that are the results of the way the

current system is implemented

– Reduce the risk of missing requirements

– Allow us to communicate with end users

– Help analysts and users understand business

terminology and rules

Process Modeling

• The simplest process model of a system is based

on inputs, outputs, and the system itself –

– Process is work performed on, or in response to,

incoming data flows or conditions

Process Modeling

• Graphically represent the processes that capture,

manipulate, store and distribute data between a system and its environment and among system components

• Data flow diagrams (DFD)

– Graphically illustrate movement of data between

external entities and the processes and data stores within a system

• Modeling a system’s process

– Utilize information gathered during requirements

determination– Structure of the data is also modeled in addition to the processes

8.8

Process Modeling

• Deliverables and Outcomes

– Set of coherent, interrelated data flow diagrams

– Context data flow diagram (DFD)

• Scope of system

– DFDs of current system

• Enables analysts to understand current system

– DFDs of new logical system

Data Flow Diagrams

• Data modeling is done during the project definition stage and refined in physical design

• Similar to ERD Data model - DFD also helps the analyst

identify business vocabulary and uncover business

requirements

• Can be used on current system to understand requirements

• Can be fit on several sheets of paper

• The level of data flow diagram can be compared to a

highway and street maps that you might use - National => State => City

Data Flow Diagrams

 Tool that depicts the flow of data through a system and the work or processing performed by that system

Graphical tool used to describe and analyze the movement of data through a system manual or automated

 Central tool in which other components are developed

A data flow diagram (DFD) is a tool that depicts the flow of data through a system and the work or processing performed by that system Synonyms include bubble chart, transformation

graph, and process model

DFD Symbols

• Named vector or arrow

– Called a data flow

– Portrays a data path

• Bubble

– Called a process

– Portrays transformation of data

• Narrow open rectangle

– Called a data store

– Portrays a file or data base

• Box

– Called a source or sink

– Portrays an internal or external agent

– Used to define a system’s boundaries

new order

3.2

Verify Credit

Verify Credit 3.2

Customer Master File

Customer

DFD Symbols

• Data flow - data move in a specific direction

• Processes - people, procedures or device that transforms data - work to be done

• Source or destination - external source or destination of data which may be people, program, organization or other entities - The squares represent external agents – the

boundary of the system

• Data Store - where data is house

Sold 2.0

Credit History

Accepted Orders

External

Entity

Data Store

Process Data Flow

DFD Symbols

Data Flow

• A data flow is data in motion

• The flow of data between a system and its environment, or between two processes inside a system an relationship

between a system and its environment, or between two

processes is communication

– A data flow represents an input of data to a process,

or the output of data (or information) from a process

A data flow is also used to represent the creation,

deletion, or update of data in a file or database (called

a data store on the DFD)

– A data flow is depicted as a solid-line with arrow

Data Flow

3.1.2 Create a new member account

3.1.1 Generate an employee bank statement

3.1.3 Freeze member account number

Accounts Receivable Department

Frozen account notification

Employee address

Bank statement Membership

application

Data Flow

• No data flow should ever go completely unnamed

• Data flow names should describe the data flow without describing how the flow is or could be implemented

• All data flows must begin or end at a process, because

data flows are the inputs and outputs of a process

• Naming Convention - Should be descriptive nouns and noun phrases that are singular, as opposed to plural

– Should be unique

• Use adjectives and adverbs to help to describe how processing has changed a data flow

Data Flow

Orders

Process Order

Cencel Order

Change Order Address

Summarize Unfilled Orders

Order

Cancelled Order

Change of Address Summary of Orders

New Order Address

Unfilled Order l

New Order

Order

to be Deleted 2

1 2

2

Data Flow Packet Concept

• Data is seen as a package of information

Telephone Service Provider

Pay phone bill

Itemized calls and invoice

Itemized calls Invoice

Correct use of the packet concept

Incorrect use of the packet concept

Data Stores

• Most information systems capture data for later use

• The data is kept in a data store

– A data store is an ``inventory’’ of data Synonyms

include file and database (although those terms are too implementation-oriented for essential process

modeling)

– A data store is represented by the open-end box

• If data flows are data in motion, think of data stores as data at rest

• Data stores should describe ``things’’ about which the

business wants to store data

• It is permissible to duplicate data stores on a DFD to

avoid crossing data flow lines

Data Stores

• Data cannot be moved from one data store to another data stored it must be moved by a process

• Data cannot be moved from an outside source to a data

store it must be moved by a process

• Data Stores should have noun phrase labels

• Data Stores can be labeled

• Data flow to a data store means new/update

• Data flow from a data store means retrieve

Good Sold File

A

DFD Rules - Data Stores

Good Sold File

Inventory

Good Sold File

Manager

Produce Mgmt Reports

DFD Rules - Data Stores

Good Sold File

Inventory

Good Sold File

Manager

Produce Mgmt Reports

Inventory Data Student Data

Sold data Sold data

Process

• Process names should be descriptive

• Processes should have a single Action Verb and a Singular Object

• Process numbers strictly used for identification

• All Processes are connected to something

• All Processes have both Inputs and Outputs

• No Process has only outputs or only inputs

• Processes may connect to anything: other processes, data stores or entities

• Each Process has a unique name and number

• A Process number is used only once in a diagram set

Process Customer Food Order 1.0

1Process 1

Process Example

Process Customer Food Order 1.0

Process Customer Food Order 1.0

Which ones are correct and incorrect?

External Entities

External Entities

• All information systems respond to events and conditions

in the environment

• The environment of an information system includes

external entities that form the boundary of the system, and define places where the system interfaces with its environment

• A external entity defines an a person, organization unit, other system, or other organization that lies outside of the scope of the project, but which interacts with the system being studied

• External agents provide the net inputs into a system, and receive net outputs from a system

• Common synonyms include external agents

• External agents should be named with descriptive, singular nouns.

• As a general rule, external agents should be located on the perimeters of the page, consistent with their definition as

a system boundary

Data Flow Diagramming Definitions

• Context Diagram

– A data flow diagram (DFD) of the scope of an organizational system that shows the system boundaries, external entities that interact with the system and the major information flows between the entities and the system

• Level-O Diagram

– A data flow diagram (DFD) that represents a system’s major processes, data flows and data stores at a high level of detail

8.33

Fast Food Restaurant

• Context diagram an overview of an organization system that shows

– the system boundaries

– sources that interact with the system

– major information flow between the entities

Fast Food Restaurant

• The Context Diagram

– The context diagram contains one and only one process.– External entities are drawn around the perimeter

– Data flows define the interactions of your system with the boundaries and with the external data stores

– Refer as Level Zero

• Let’s draw a context diagram

– What does a restaurant do - think McDonalds or

Hoosier

– What are the boundaries

– Who does it interact with

Figure 8-4

Context diagram of Hoosier Burger’s food ordering system

8.37

Figure 8-5

Level-0 DFD of Hoosier Burger’s food ordering system

8.38

Data Flow Diagramming Rules

• Source/Sink

– Data cannot move directly from a source to

a sink – A source/sink has a noun phrase label

• Data Flow

– A data flow has only one direction of flow between symbols

– A fork means that exactly the same data goes from a common location to two or more processes, data stores

or sources/sinks

8.39

Data Flow Diagramming Rules

• Data Flow (Continued)

– A join means that exactly the same data comes from any

two or more different processes, data stores or sources/sinks to a common location

– A data flow cannot go directly back to the same process it

leaves

– A data flow to a data store means update

– A data flow from a data store means retrieve or use

– A data flow has a noun phrase label

8.40

Data Flow Example

DFD Rules Data Flow

What are the rules

violations?

Entity B

2

Process Green

2.1

Process BlueEntity A

Data Store 1 Dataflow 2

• Level-N Diagrams

– A DFD that is the result of n nested decompositions of a series of subprocesses from a process on a level-0 diagram

8.46

Relationship Among DFD levels

Level 0 Diagram

• Shows all the processes that comprise the overall system

• Shows how information moves from and to each process

• Adds data stores

Level 1 Diagrams

• Shows all the processes that comprise a single process on the level 0 diagram

• Shows how information moves from and to each of these processes

• Shows in more detail the content of higher level process

• Level 1 diagrams may not be needed for all level 0 processes

Level 2 Diagrams

• Shows all processes that comprise a single process on the level 1 diagram

• Shows how information moves from and to each of these processes

• Level 2 diagrams may not be needed for all level 1 processes

• Correctly numbering each process helps the user understand where the process fits into the overall system

• The Data Flow Diagram (DFD) is an essential tool for creating formal descriptions of business processes and data flows.

• Use cases record the input, transformation, and output of business processes.

• Eliciting scenario descriptions and modeling business processes are critically important skills for the systems analyst to master.

Balancing DFDs

• When decomposing a DFD, you must conserve inputs to and outputs from a process at the next level of decomposition

• This is called balancing

• Example: Hoosier Burgers

– In Figure 8-4, notice that there is one input to the system, the customer order

8.52

Figure 8-4

Context diagram of Hoosier Burger’s food ordering system

8.53

Figure 8-5

Level-0 DFD of Hoosier Burger’s food ordering system

8.54

Balancing DFDs

• An unbalanced example

– Figure 8-10– In context diagram, we have one input to the system, A and one output, B

– Level-0 diagram has one additional data flow, C– These DFDs are not balanced

8.55

DFD: Balancing and Leveling

• When Zooming In, Do Not forget the Parent!

– Parent Process

– Child Diagram

P1

P1.2 P1.1

DFD: Exercise Problem Level 0

DFD: Exercise Problem Level 1

DFD: Exercise Problem Level 2

Four Different Types of DFDS

• Current Physical

– Process label includes an identification of the technology (people or systems) used to process the data

– Data flows and data stores are labeled with the actual name of the physical media on which data flow or in which data are stored

8.61

Four Different Types of DFDS

• New Physical

– Represents the physical implementation of the new system

8.62

Guidelines for Drawing DFDs

• Completeness

– DFD must include all components necessary for system– Each component must be fully described in the project dictionary or CASE repository

• Consistency

– The extent to which information contained on one level

of a set of nested DFDs is also included on other levels

• Timing

– Time is not represented well on DFDs– Best to draw DFDs as if the system has never started and will never stop

8.63

Guidelines for Drawing DFDs

• Rules for stopping decomposition

– When each process has been reduced to a single decision, calculation or database operation

– When each data store represents data about a single entity

– When the system user does not care to see any more detail

8.64

Using DFDs as Analysis Tools

• Gap Analysis

– The process of discovering discrepancies between two

or more sets of data flow diagrams or discrepancies within a single DFD

• Inefficiencies in a system can often be

identified through DFDs

8.65

Oracle’s Process Modeler and

Functional Hierarchy Diagrams

• Process Modeler

– Unique to Oracle – Similar to DFDS but outputs and methods differ in several ways.

– Table 8-4 illustrates differences

• Functional Hierarchy Diagrams

– Picture of various tasks performed in a business and how they are related

– Tasks are broken down into their various parts – Does not include data flows

8.66

• Data flow diagrams (DFD)

– Symbols – Rules for creating – Decomposition – Balancing

• Four different kinds of DFDs

– Current Physical – Current Logical – New Logical – New Physical

8.67

• DFDs for Analysis

• DFDs for Business Process Reengineering (BPR)

• Oracle’s Process Modeler

• Functional Hierarchy Diagrams

8.68