Systems Analysis and Design Allen Dennis and Barbara Haley ...

Systems Analysis and Design Allen Dennis and Barbara Haley ...

Business Process Management Key Definitions Process model A formal way of representing how a business operates Illustrates the activities that are performed and how data moves among them

Data flow diagramming A popular technique for creating process models Key Definitions Logical process models describe processes without suggesting how they are conducted

Physical process models include process implementation information DATA FLOW DIAGRAMS Reading a DFD DFD Elements

Process An activity or function performed for a specific business reason Manual or computerized Data flow A single piece of data or a logical collection of data Always starts or ends at a process

DFD Elements Data Store A collection of data that is stored in some way Data flowing out is retrieved from the data store Data flowing in updates or is added to the data store External entity

A person, organization, or system that is external to the system but interacts with it. 6 -7 Naming and Drawing DFD Elements Process Data flow Data store External

entity Depicting Business Processes with DFDs 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 Key Definition Balancing involves insuring that information presented at one level of a DFD is accurately represented in the next level DFD.

Relationship Among DFD levels Context diagram Level 0 diagram Level 1 diagram Level 2 diagram

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

Level 0 Diagram Shows all the major processes that comprise the overall system the internal components of process 0 Shows how the major processes are interrelated by data flows Shows external entities and the major processes with which they interact Adds data stores

Level 1 Diagrams 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 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 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 Data Flow Splits and Joins A data flow split shows where a flow is broken into its component parts for use in separate processes Data flow splits need not be mutually

exclusive nor use all the data from the parent flow As we move to lower levels we become more precise about the data flows A data flow join shows where components are merged to describe a more comprehensive flow Alternative Data Flows Where a process can produce different

data flows given different conditions We show both data flows and use the process description to explain why they are alternatives Tip -- alternative data flows often accompany processes with IF statements CREATING DATA FLOW DIAGRAMS

Steps in Building DFDs Build the context diagram Create DFD fragments or an event table Organize DFD fragments into level 0 diagram Decompose 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 Diagram Draw one process representing the entire system (process 0) Find all inputs and outputs listed from the use cases (or event table) that come from or go to external entities; draw as data flows

Draw in external entities as the source or destination of the data flows A Context Diagram Example Creating DFD Fragments Add data flows to show use to data stores as sources and destinations

of data Layouts typically place processes in the center inputs from the left outputs to the right stores beneath the processes A DFD Fragment Example Creating the Level 0

Diagram Combine the set of DFD fragments into one diagram Generally move from top to bottom, left to right Minimize crossed lines Iterate as needed DFDs are often drawn many times before being finished, even with very experienced systems analysts

A Level 0 DFD Example Creating Level 1 Diagrams (and Below) Input data flows shown on a parent DFD are often unbundled on the child diagram using splits Output data flows shown on a child DFD are often bundled using joins

and shown as a larger data flow on the parent diagram When to stop decomposing DFDs? Ideally, a DFD has at least 3 processes and no more than 7-9. Validating the DFD Syntax errors diagram follows the rules Assure correct DFD structure For each DFD:

Check each process for: A unique name: action verb phrase; number; description At least one input data flow At least one output data flow Output data flow names usually different than input data flow name Between 3 and 7 processes per DFD Validating the DFD 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 Check each data store for: A unique name: noun; description At least one input data flow At least one output data flow

Check each external entity for: A unique name: noun; description At least one input or output data flow Validating the DFD 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 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 Validating the DFD Semantics errors diagram conveys correct meaning Assure accuracy of DFD relative to actual/desired business processes To verify correct representation, use

User walkthroughs Role-play processes Examine lowest level DFDs to ensure consistent decomposition Examine names carefully to ensure consistent use of terms

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