DFD examples

Creating DFDs Define Entities Define Processes External entities represent persons, processes or machines which produce data to be used by the system or receive data that is output by the system Examples: Student, Customer, Client Define Processes Processes are discrete actions that transform input data to output data Examples: Create Student Record, Calculate Purchase Cost, Register Client Student 2.1 Create Student Record

Creating DFDs (cont’d) Define Data Stores Data stores are temporary or permanent repositories of information that are inputs to or outputs of processes Examples: Student Master, Client List Define Data Flows Data flows represent the transfer of data over time from one “place” (entity, process, data store) to another Examples: New Student Information (from Student, to Student Master) Student Master D3 New Student Information

Creating DFDs (cont’d) Define the System A system is the collection of all business processes which perform tasks or produce outputs we care about. It is “what happens.” The system is a single process, connected to external entities Represented in a “Context Diagram” Define Subsystems A subsystem gives a more detailed view individual processes contained in the context diagram Includes data stores, more elementary processes

DFDs Created by Top-Down Analysis Create a narrative: description of system Create a Context Diagram that contains a single process (“the system”) and all entities which share data with the system Explode the “parent” context diagram to produce a Diagram 0 (“child”) DFD Create Diagram 1, 2, …, n DFDs that represent “explosions” of Diagram 0, 1, …, n-1 DFDs until a diagram has only “primitive” processes Create process descriptions to be implemented by application programs: queries, macros, reports, programming languages Context Diagram Diagram 0 DFD Diagram 1 DFDs Diagram n DFDs Narrative E-R Diagram Process Descriptions

Where to Begin Creating DFDs Start with the data flow from an external entity and work forwards Start with the data flow to an external entity and work backwards Examine the data flows into or out of a data store Examine data flows, entity connections and data stores associated with a particular process Note fuzzy, ill-defined areas of the system for further clarification

What to Avoid in DFDs Processes with no outputs or no inputs 4 Perform Repair Processes with no outputs or no inputs Processes whose inputs are obviously inadequate to yield outputs Connecting data stores directly to each other Class List Courses Students Having data flows terminate at data stores Connecting entities to anything other than processes Payroll Department Employees Making the data flow diagram too cluttered (e.g.  9 processes) 1 2 3 Many processes with a single input and output (linear flow) Process A Process B Process C

Creating Data Flow Diagrams Lemonade Stand Example

Creating Data Flow Diagrams Example Steps: The operations of a simple lemonade stand will be used to demonstrate the creation of dataflow diagrams. Create a list of activities Old way: no Use-Case Diagram New way: use Use-Case Diagram Construct Context Level DFD (identifies sources and sink) Construct Level 0 DFD (identifies manageable sub processes ) Construct Level 1- n DFD (identifies actual data flows and data stores )

Creating Data Flow Diagrams Example Create a list of activities Think through the activities that take place at a lemonade stand. Customer Order Serve Product Collect Payment Produce Product Store Product

Creating Data Flow Diagrams Example Create a list of activities Also think of the additional activities needed to support the basic activities. Customer Order Serve Product Collect Payment Produce Product Store Product Order Raw Materials Pay for Raw Materials Pay for Labor

Creating Data Flow Diagrams Example Create a list of activities Group these activities in some logical fashion, possibly functional areas. Customer Order Serve Product Collect Payment Produce Product Store Product Order Raw Materials Pay for Raw Materials Pay for Labor

Creating Data Flow Diagrams Example Construct Context Level DFD (identifies sources and sink) Create a context level diagram identifying the sources and sinks (users). Context Level DFD Sales Forecast CUSTOMER 0.0 Lemonade System EMPLOYEE Order Production Schedule Customer Order Serve Product Collect Payment Produce Product Store Product Order Raw Materials Pay for Raw Materials Pay for Labor Product Served Pay Payment Time Worked Received Goods Payment Purchase Order VENDOR

Creating Data Flow Diagrams Example Construct Level 0 DFD (identifies manageable sub processes ) Create a level 0 diagram identifying the logical subsystems that may exist. Level 0 DFD 1.0 Sale Sales Forecast Customer Order Serve Product Collect Payment Produce Product Store Product Order Raw Materials Pay for Raw Materials Pay for Labor Customer Order Product Ordered CUSTOMER Payment 2.0 Production EMPLOYEE Production Schedule Product Served Inventory Received Goods VENDOR 3.0 Procure-ment Purchase Order Order Decisions Payment Pay Time Worked 4.0 Payroll

Creating Data Flow Diagrams Example Construct Level 1- n DFD (identifies actual data flows and data stores ) Create a level 1 decomposing the processes in level 0 and identifying data stores. Level 1 DFD CUSTOMER Customer Order Request for Forecast Customer Order Serve Product Collect Payment Produce Product Store Product Order Raw Materials Pay for Raw Materials Pay for Labor ORDER 1.1 Record Order 1.3 Produce Sales Forecast Severed Order Payment Sales Forecast 1.2 Receive Payment PAYMENT

Creating Data Flow Diagrams Example Construct Level 1 (continued) Create a level 1 decomposing the processes in level 0 and identifying data stores. Level 1 DFD Product Order ORDER 2.1 Serve Product Customer Order Serve Product Collect Payment Produce Product Store Product Order Raw Materials Pay for Raw Materials Pay for Labor Quantity Severed RAW MATERIALS Production Schedule 2.2 Produce Product Quantity Used INVENTORTY Production Data 2.3 Store Product Quantity Produced & Location Stored

Creating Data Flow Diagrams Example Construct Level 1 (continued) Create a level 1 decomposing the processes in level 0 and identifying data stores. Level 1 DFD Order Decision PURCHASE ORDER 3.1 Produce Purchase Order Customer Order Serve Product Collect Payment Produce Product Store Product Order Raw Materials Pay for Raw Materials Pay for Labor Quantity On-Hand RAW MATERIALS Quantity Received Received Goods 3.2 Receive Items RECEIVED ITEMS Payment Approval 3.3 Pay Vendor VENDOR Payment

Creating Data Flow Diagrams Example Construct Level 1 (continued) Create a level 1 decomposing the processes in level 0 and identifying data stores. Level 1 DFD Time Worked TIME CARDS 4.1 Record Time Worked Customer Order Serve Product Collect Payment Produce Product Store Product Order Raw Materials Pay for Raw Materials Pay for Labor Employee ID EMPLOYEE Payroll Request 4.2 Calculate Payroll Unpaid time cards PAYROLL Payment Approval 4.3 Pay Employee PAYMENTS Payment

Process Decomposition 1.0 Sale 1.1 Record Order 1.2 Receive Payment 2.0 Production 2.1 Serve Product 2.2 Produce Product 2.3 Store Product 0.0 Lemonade System 3.0 Procure-ment 3.1 Produce Purchase Order 3.2 Receive Items 3.3 Pay Vendor 4.0 Payroll 4.1 Record Time Worked 4.2 Calculate Payroll 4.3 Pay Employee Context Level Level 0 Level 1

DFD Example: Bus Garage Repairs Buses come to a garage for repairs. A mechanic and helper perform the repair, record the reason for the repair and record the total cost of all parts used on a Shop Repair Order. Information on labor, parts and repair outcome is used for billing by the Accounting Department, parts monitoring by the inventory management computer system and a performance review by the supervisor. Key process (“the system”): performing repairs and storing information related to repairs External Entities: Bus, Mechanic, Helper, Supervisor, Inventory Management System, Accounting Department, etc. Processes: Record Bus ID and reason for repair Determine parts needed Perform repair Calculate parts extended and total cost Record labor hours, cost

DFD Example: Bus Garage Repairs (cont’d) Data stores: Personnel file Repairs file Bus master list Parts list Data flows: Repair order Bus record Parts record Employee timecard Invoices

Bus Garage Context Diagram Mechanical problem to be repaired Fixed mechanical problems Supervisor Helper Bus Repair Process Repair summary Labor List of parts used Inventory Management System Labor Labor, parts cost details Mechanic Accounting