 During systems development both processes and data must be modeled ◦ Data modeling describes data used by system ◦ Process modeling describes processes carried out by system  Level of detail ◦ Varies between highest summary and lowest detail ◦ Structured tools enable level of detail to be varied

 Restrict a single DFD to no more than six to eight processes  Use another tool to document the lowest level of detail but use no more than a single page. B-3

 Graphic representation of a system that uses a small number of symbol shapes to illustrate how data flows through interconnected processes ◦ Most natural way to document processes ◦ Emphasis on processes rather than data B-4

Company Customer Despatch Note + Goods Order Rejected Order Context Diagram

Customer Sales1 Order Rejected Order Dispatch Note 2Warehouse Dispatch Goods 3 Accounts Maintain Credit Ratings D1Credit Rating Check Credit Rating A Complete DFD

Data Flow Diagrams (DFDs) show: The processes within the system The datastores (files) supporting its operation The information flows within it The system boundary Interactions with external entities

 DFDs consist of four symbols 1) Environmental elements called terminators / external entity  Person  Organization  Another system 2) Processes which transform inputs to outputs  Labeled with verb and object  Also labeled with system or computer program name B-8

 DFD symbols [cont.] ◦ Data flows which consist of logically related data elements that travel from one point or process to another. In other words, data in motion.  Structures  Diverge  Converge ◦ Data stores which are data repositories. In other words, data at rest. B-9

Customer Sales Check Credit Rating D1Credit Rating A Data Flow An External Entity A Process A Data Store 3 DFD Symbols

Sales Check Credit Rating 3 Unique NumberWhere it’s done What’s done Output Data Input Data The Process Symbol

Accounts Maintain Credit Rating 3 Sales Check Credit Rating 1 M = Manual data Store D = Computer File D1Credit Rating Writing/Updating Reading The data store symbol

Sales Check Credit Rating 3 D1Credit Rating The Data Flow Symbol Customer Balance Use Meaningful names Self Evident Data Flows need not be named

Physical Resource Flow Customer Returned Library Book

The External Entity Symbol Customer System Boundary A Source and/or sink of data outside the system boundry

 Context Diagram  Diagram 0  Child diagram (level 1, 2,…,n)

 DFD dikelompokkan menjadi 2: ◦ Logical DFD  Fokus pada bisnis dan bagaimana bisnis berjalan  How the system will be constructed ◦ Physical DFD  How the system will be implemented  Include hardware, software, files, people yang terlibat dalam sistem

2Dispatch Goods 2 1 Process 2.1 Dispatch Note Validated Order Levelling – to avoid complex DFDs, processes can be grouped into higher level processes

Customer Sales1 Order Rejected Order Dispatch Note 2Warehouse Dispatch Goods 3 Accounts Maintain Credit Ratings D1Credit Rating Check Credit Rating A Complete DFD

Customer D1Credit Rating A Duplicated External Entity Duplicated Data Store Customer Repeated Symbols – to avoid crossing lines, data stores and external entities can be repeated:

Level 1 Level 2 E F D Elementary Functional Description Get cust dets If order>cred refer Else raise order ….. DFD Levels

A wines and spirits wholesaler stocks a range of approximately 400 different lines and delivers by van on regular weekly runs to customers who are mainly off-licenses and clubs. The majority of orders are received by telephone and any one customer may place several orders during the week which must be accumulated and delivered in one consignment. When a customer telephones he expects to be advised on the availability of an item requested and, if not in stock, the alternatives that are available. At present, sales order forms are filled in by the telephone salesmen and sent to the warehouse where they are used for the despatch of the items. Hand-written despatch notes are used as the basis of the invoices which are typed and sent by post sometime later. Prepare a dataflow diagram (DFD) which represents the above system. Sample

Developing Dataflow Diagrams 1. Identify external entities 2. Draw context diagram 3. Who/Where does what 4. Identify datastores 5. Draw diagram

External Entities 1.Customer Context Diagram customer company order invoice advice des. note + goods

WhatWhere/who Receive ordersSales Accumulate ordersSales Advise availabilitySales Complete Sales Order FormSales Despatch ItemsWarehouse Write despatch notesWarehouse Type InvoicesWarehouse Send InvoicesWarehouse Datastore Stock file

customer Stock file Accumulate orders Advise availability Complete forms 1Sales Sales Order Forms 2 Produce despatch notes Produce Invoices InvoiceDespatch note + goods Warehouse Draw DFD Order Advice M1

Extensions Maintenance of Stock File Customer file – address, credit etc Payments Accounts dept – invoices, payments etc Accumulate orders – temporary file