Software Analysis 1 PROCESS MODELING: Data Flow Diagrams (DFDs)

Software Analysis 2 PROCESS MODELING Graphically represent the processes that capture, manipulate, store and distribute data Use information gathered during requirements gathering.

A top down system Level 0 The context level Also called context diagram Relationship between system and environment Software Analysis 3

4 DFD Symbols (Gane & Sarson) Process Data Flow Data Store Source/Sink (External Entity)

Software Analysis 5 Data Flow Diagramming Rules Inputs to a process are always different than outputs Objects always have a unique name

Software Analysis 6 Process Work or actions performed on data (inside the system  internal to the system) Labels should be verb phrases Receives input data and produces output (no process can have only outputs – a miracle-, & no process can have only inputs –black hole)

Software Analysis 7 Processes Examples of processes include those that:  Perform computations  Make decisions  Sort, filter or otherwise summarize data  Organize data into useful information  Use stored data (create, read, update or delete a record)

Software Analysis 8 Data Flow Is a path for data to move from one part of the IS to another Arrows depicting movement of data Can represent flow between process and data store by two separate arrows

Software Analysis 9 Data in motion, moving from one place to another in the system  From external entity (source) to system  From system to external entity (sink)  From internal symbol to internal symbol, but always either start or end at a process Data Flow

Software Analysis 10 Data Flow: Correct/Incorrect? A B

Software Analysis 11 Data Store Depicts data at rest Include in system if the system processes transform the data  Store, Add, Delete, Update Every data store on DFD should correspond to an entity on an ERD Labels should be noun phrases The name of the store as well as the number are recorded in between lines

Software Analysis 12 Rule: Data Store Must have at least one incoming and one outgoing data flow

Software Analysis 13 Data cannot be moved directly from one store to another Data cannot move directly from an outside source to a data store Data cannot move directly from a data store to a data sink Rule: Data Store (2)

Software Analysis 14 Source/Sink (External Entity) External entity that is origin or destination of data (outside the system) Is the singular form of a department, outside organization, other IS, or person Labels should be noun phrases Source – Entity that supplies data to the system Sink – Entity that receives data from the system

Software Analysis 15 Rule: Source/Sink Must be connected to a process by a data flow

Software Analysis 16 Source/Sink: Correct/Incorrect?