Session 4 Process Modeling - Universitas Indonesia · PowerPoint Course Material for SCELE Graduate Program Information Technology ... the system in a hierarchy of DFD diagrams Child

PowerPoint Course Material for SCELE Graduate Program Information TechnologyFaculty of Computer Science – UNIVERSITY OF INDONESIA

PERANCANGAN SISTEM INFORMASI

Session 4 Process Modeling

Based on System Analysis & Design 2nd EditionAuthors : Alan Dennis & Barbara Haley Wixom

Publisher : John Wiley & Sons

Session 4 Process ModelingSession 4 Process Modeling

Based on System Analysis & Design 2nd EditionAuthors : Alan Dennis & Barbara Haley Wixom

Publisher : John Wiley & Sons

2PowerPoint Course Material for SCELE Graduate Program Information TechnologyFaculty of Computer Science – University of Indonesia

ObjectivesObjectives

Understand the rules and style guidelines for data flow diagrams.Understand the process used to create data flow diagrams.Be able to create data flow diagrams.


Key DefinitionsKey Definitions

Process modelA formal way of representing how a business operatesIllustrates the activities that are performed and how data moves among them

Data flow diagrammingA popular technique for creating process models


Key DefinitionsKey Definitions

Logical process models - describe processes without suggesting how they are conductedPhysical process models - include process implementation information


DATA FLOW DIAGRAMS


Reading a DFDReading a DFD


DFD Elements (1/2)DFD Elements (1/2)

ProcessAn activity or function performed for a specific business reasonManual or computerized

Data flowA single piece of data or a logical collection of dataAlways starts or ends at a process


DFD Elements (2/2)DFD Elements (2/2)

Data StoreA collection of data that is stored in some wayData flowing out is retrieved from the data storeData flowing in updates or is added to the data store

External entityA person, organization, or system that is external to the system but interacts with it.


Naming and Drawing DFD ElementsNaming and Drawing DFD Elements

Process

Data flow

Data store

Externalentity


Depicting Business Processes with DFDsDepicting Business Processes with DFDs

Business processes are too complex to be shown on a single DFDDecomposition is the process of representing the system in a hierarchy of DFD diagrams

Child diagrams show a portion of the parent diagram in greater detail


Key DefinitionKey Definition

Balancing involves insuring that information presented at one level of a DFD is accurately represented in the next level DFD.


Relationship Among DFD levelsRelationship Among DFD levels

Context diagram

Level 0 diagram

Level 1 diagram


Context DiagramContext Diagram

First DFD in every business processShows the context into which the business process fitsShows the overall business process as just oneprocess (process 0)Shows all the external entities that receive information from or contribute information to the system


Level 0 DiagramLevel 0 Diagram

Shows all the major processes that comprise the overall system – the internal components of process 0Shows how the major processes are interrelated by data flowsShows external entities and the major processes with which they interactAdds data stores



Generally, one level 1 diagram is created for every major process on the level 0 diagramShows all the internal processes that comprise a single process on the level 0 diagramShows how information moves from and to each of these processesIf a parent process is decomposed into, for example, three child processes, these three child processes wholly and completely make up the parent process



Shows all processes that comprise a single process on the level 1 diagramShows how information moves from and to each of these processesLevel 2 diagrams may not be needed for all level 1 processesCorrectly numbering each process helps the user understand where the process fits into the overall system


Data Flow Splits and JoinsData Flow Splits and Joins

A data flow split shows where a flow is broken into its component parts for use in separate processesData flow splits need not be mutually exclusive nor use all the data from the parent flowAs we move to lower levels we become more precise about the data flowsA data flow join shows where components are merged to describe a more comprehensive flow


Alternative Data FlowsAlternative Data Flows

Where a process can produce different data flows given different conditionsWe show both data flows and use the process description to explain why they are alternativesTip -- alternative data flows often accompany processes with IF statements


Your TurnYour Turn

At this point in the process it is easy to lose track of the “big picture”. Describe the difference between data flows, data stores, and processes. Describe in your own words the relationship between the DFD and the ultimate new application being developed.


Process DescriptionsProcess Descriptions

Text-based process descriptions provide more information about the process than the DFD aloneIf the logic underlying the process is quite complex, more detail may be needed in the form of

Structured EnglishDecision TreesDecision Tables


Structured EnglishStructured English

Common Statements Example

Action Statement Profits = Revenues - ExpensesGenerate Inventory ReportAdd Product record to Product Data Store

If Statement IF Customer Not in Customer Data StoreTHEN Add Customer record to Customer Data StoreELSE Add Current Sale to Customer’s Total Sales

Update Customer record in Customer Data Store

For Statement FOR all Customers in Customer Data Store, doGenerate a new line in the Customer ReportAdd Customer’s Total Sales to Report Total

Case Statement CASEIf Income < 10,000: Marginal tax rate = 10%If Income < 20,000: Marginal tax rate = 20%If Income < 30,000: Marginal tax rate = 31%If Income < 40,000: Marginal tax rate = 35%ELSE Marginal tax rate = 38%

ENDCASE


Decision TreesDecision Trees

Graphical way of depicting if-then-else logic


Decision TablesDecision Tables

Represent very complex processes with multiple decision rules


CREATING DATA FLOW DIAGRAMS


Integrating Scenario DescriptionsIntegrating Scenario Descriptions

DFDs start with the use cases and requirements definitionGenerally, the DFDs integrate the use casesNames of use cases become processesInputs and outputs become data flows“Small” data inputs and outputs are combined into a single flow


Steps in Building DFDsSteps in Building DFDs

Build the context diagramCreate DFD fragments for each use caseOrganize DFD fragments into level 0 diagramDecompose level 0 processes into level 1 diagrams as needed; decompose level 1 processes into level 2 diagrams as needed; etc.Validate DFDs with user to ensure completeness and correctness


Build the Context DiagramBuild the Context Diagram

Draw one process representing the entire system (process 0)Find all inputs and outputs listed at the top of the use cases that come from or go to external entities; draw as data flowsDraw in external entities as the source or destination of the data flows


A Context Diagram ExampleA Context Diagram Example


Creating DFD FragmentsCreating DFD Fragments

Each use case is converted into one DFD fragmentNumber the process the same as the use case numberChange process name into verb phraseDesign the processes from the viewpoint of the organization running the system


Creating DFD FragmentsCreating DFD Fragments

Add data flows to show use to data stores as sources and destinations of dataLayouts typically place

processes in the centerinputs from the leftoutputs to the rightstores beneath the processes


A DFD Fragment ExampleA DFD Fragment Example


Creating the Level 0 DiagramCreating the Level 0 Diagram

Combine the set of DFD fragments into one diagramGenerally move from top to bottom, left to rightMinimize crossed linesIterate as needed

DFDs are often drawn many times before being finished, even with very experienced systems analysts


A Level 0 DFD ExampleA Level 0 DFD Example


Creating Level 1 Diagrams (and Below)Creating Level 1 Diagrams (and Below)

Each use case is turned into its own DFDTake the steps listed on the use case and depict each as a process on the level 1 DFDInputs and outputs listed on use case become data flows on DFDInclude sources and destinations of data flows to processes and stores within the DFDMay also include external entities for clarity


Creating Level 1 Diagrams (and Below)Creating Level 1 Diagrams (and Below)

Input data flows shown on a parent DFD are often unbundled on the child diagram using splitsOutput data flows shown on a child DFD are often bundled using joins and shown as a larger data flow on the parent diagramWhen to stop decomposing DFDs?

Ideally, a DFD has at least 3 processes and no more than 7-9.


Validating the DFDValidating the DFD

Syntax errors – diagram follows the rulesAssure correct DFD structure

For each DFD:Check each process for:

A unique name: action verb phrase; number; descriptionAt least one input data flowAt least one output data flowOutput data flow names usually different than input data flow namesBetween 3 and 7 processes per DFD


Validating the DFDValidating the DFD

Semantics errors – diagram conveys correct meaning

Assure accuracy of DFD relative to actual/desired business processes

To verify correct representation, useUser walkthroughsRole-play processes

Examine lowest level DFDs to ensure consistent decompositionExamine names carefully to ensure consistent use of terms


SummarySummary

The Data Flow Diagram (DFD) is an essential tool for creating formal descriptions of business processes.Use cases record the input, transformation, and output of business processes and are the basis for process models.Eliciting use cases and modeling business processes are critically important skills for the systems analyst to master.

Documents

Session 4 Process Modeling - Universitas Indonesia · PowerPoint Course Material for SCELE Graduate Program Information Technology ... the system in a hierarchy of DFD diagrams Child