System analysis and design - Safaa-Dalloul

System analysis and design - Safaa-Dalloul

N A S I S Y L A

O M L E N AL T D S .

G I Y .Y S ES A S D A FA S U

L D N A DATA FLOW DIAGRAMS

UNIT 6: DATA FLOW DIAGRAMS Creating Data Flow Diagrams Introduction Data Flow Diagrams (DFD) Reading Data Flow Diagrams Elements of Data Flow

Diagrams Using DFD to Define Business Process Process Descriptions Creating Data Flow Diagrams Context Diagram Level 0 Diagram

Level 1 Diagram (and Below) Validating Data Flow Diagrams CREATING DATA FLOW DIAGRAMS Process model describes business process-the activities that people do. Process models are developed for the asis system and/or the to-be system. Data flow diagramming, one of the most commonly used

process modeling techniques. INTRODUCTION Process model A formal way of representing how a business system operates. Illustrates/Explain the activities that are performed and how data moves among them. Data flow diagramming A common technique for creating process models

INTRODUCTION Logical process models describe suggesting how they are conducted processes without

Physical process models provide information that is needed to build the system ELEMENTS OF DFD ELEMENTS OF DFD USING DFD TO DEFINE BUSINESS PROCESS

Business processes are too complex to be shown on a single DFD. Decomposition 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. Balancing involves insuring that information presented at one level of a DFD is accurately represented in the next level DFD.

USING DFD TO DEFINE BUSINESS PROCESS PROCESS DESCRIPTIONS Text-based process descriptions provide more information about the process than the DFD alone. If the logic underlying the process is quite complex, more detail may be needed in the form of

Structured English Decision trees Decision tables CREATING DATA FLOW DIAGRAMS CONTEXT DIAGRAMS The first DFD in every business process model. Context Diagram shows the entire system as context with

it's environment. All process models have only one context diagram. Context diagram shows overall process as just one process. Context Diagram shows data flows with external entities or/and any other systems in the organization. CONTEXT DIAGRAMS

CONTEXT DIAGRAMS In a Patient Information system in a hospital, the system will interact with three entities (Patient, Insurance company, and doctors). CONTEXT DIAGRAMS There are many data exchanging between the system and the patient, such as: Collect patient information (i.e. name, phone and

address ). Receive an appointment request from the patient. Receive payment information from the patient Deliver appointments schedule to the patient Deliver bills details to the patients CONTEXT DIAGRAMS And there are only two data flows with Insurance company:

Sending bills to the company And receiving Payment information CONTEXT DIAGRAMS And finally the system will produce the following reports to doctors: Appointment report Patient report Financial reports

QUESTION Draw the context diagram for student information system LEVEL 0 DIAGRAM Once you have the set of DFD fragments (One for each use case) you simply combine them into one DFD drawing that becomes Level 0 DFD. In this DFD you'll add data stores.

Level 0 diagrams show the major process within the system, and major process within external entities, which are the sources or destination of data flows. LEVEL 0 DIAGRAM Try to put the first chronologically process to the left top corner, and then draw the diagram bottom right ways. Reduce the number of crosses as few as possible. Iteration is the cornerstone of good DFD design, the first

time draw DFD to understand the system. Second iteration; draw it for better understanding and to reduce number of crosses. And so on. LEVEL 0 DIAGRAM On Doctors office system, we have four different use cases in level 1, make appointment, maintain patient info, perform billing, and prepare management reports. So you ( as analysts) have a choice to draw them all in

one diagram (witch is preferred) or to divide them into four different diagrams. The following is a cut of the level 0 diagram LEVEL 0 DIAGRAM PROCESS 1 LEVEL 0 DIAGRAM PROCESS 2 LEVEL 0 DIAGRAM PROCESS 3

LEVEL 0 DIAGRAM PROCESS 4 LEVEL 0 DIAGRAM EXPLAIN Patient provides Address). his/here

information (Name, and Process 1 checks patient's state in Patients Data Store, to update or insert Patient requests an appointment in a suitable time for

him/her. The process checks availability of these times by querying Appointments Data Store. LEVEL 0 DIAGRAM EXPLAIN Then Process 1 provides the patient with a potential appointments So the patient will select the most suitable appointment. And the Process finally updates Appointments Data Store

to assign the selected appointment. And finally informs the patient with this/here selection to be confirmed. LE VE L0 EX DIA AM GR

AM PL E LEVEL 1 DIAGRAM Generally, one level 1 diagram is created for every major process on the level 0 diagram. Shows all the internal processes that comprise a single process on the level 0 diagram.

The process for creating the level 1 DFDs is to take the steps as written on the use cases and convert them into a DFD in much the same way as for the level 0. LEVEL 1 DIAGRAM Shows how information moves from and to each of these processes If a parent process is decomposed into, for example, three child processes, these three child processes wholly

and completely make up the parent process Level 1 Diagram Example Reading Data Flow Diagrams TO EXPLAIN THE CHART

This chart for a doctor office. People start reading the diagrams from top-left corner of the DFD. The item "Patient" is an external entity. "Patient" entity has four different arrows pointing away from itself, represent bundles of data. TO EXPLAIN THE CHART Rounded rectangles such as "Get Patient Name and

Address" are actions/process that are performed. Arrows are data flows, an arrow that pointing to an entity, or pointing to a process represent the inputs for this entity or process. Arrows that pointing out of the entity/process represent outputs for this entity/process. VALIDATING DATA FLOW DIAGRAMS

VALIDATING DATA FLOW DIAGRAMS There are two fundamentally different types of problems that can occur in DFDs, syntax errors and semantic errors. Syntax Errors: refers to structure of the DFDs and whether the DFDs follow the rules of the language. Semantic Errors: refers to the meaning of the DFDs and whether they accurately describe the business process being modeled.

FOR EACH DFD: Check each data flow for: A unique name: noun; description Connects to at least one process Shown in only one direction (no two-headed arrows) A minimum number of crossed lines FOR EACH DFD:

Check each data store for: A unique name: noun; description At least one input data flow At least one output data flow FOR EACH DFD: Check each external entity for: A unique name: noun; description At least one input or output data flow

ACROSS DFDS: Context Diagram: Every set of DFDs must have one Context Diagram Viewpoint: There is a consistent viewpoint for the entire set of DFDs ACROSS DFDS:

Decomposition: Every process is wholly and complete described by the processes on its children DFDs Balance: Every data flow, data store, and external entity on a higher level DFD is shown on the lower level DFD that decomposes it No data stores or data flows appear on lower-lever DFDs that do not appear on their parent DFD.

SUMMARIZE THE LECTURE DFD DFD Elements DFD Levels Context Diagram Level 0 Level 1 Level 2 Validating DFD

L U .COM OSS L L E R A

P D D R Y. . W O . S UL S

O A L A DAL F A A S

A F A a h T k

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