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© 2010 Bennett, McRobb and Farmer1 Data Flow Diagrams Supplementary material to support Bennett, McRobb and Farmer: Object Oriented Systems Analysis and.

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Presentation on theme: "© 2010 Bennett, McRobb and Farmer1 Data Flow Diagrams Supplementary material to support Bennett, McRobb and Farmer: Object Oriented Systems Analysis and."— Presentation transcript:

1 © 2010 Bennett, McRobb and Farmer1 Data Flow Diagrams Supplementary material to support Bennett, McRobb and Farmer: Object Oriented Systems Analysis and Design Using UML, (4th Edition), McGraw Hill, 2005.

2 2© 2010 Bennett, McRobb and Farmer In This Presentation You Will Learn: What data flow diagrams (DFDs) are What DFDs can be used for Why DFDs are not used in object-oriented analysis and design Variations in notation for DFDs

3 3© 2010 Bennett, McRobb and Farmer What are DFDs? Data flow diagrams (DFDs) are one of the diagramming techniques used in structured systems analysis and design Data flow diagrams show: –Data flowing through a system to or from users (external entities) –The processes that transform the data –The data stores that hold the data

4 4© 2010 Bennett, McRobb and Farmer What do DFDs look like? 2.4 Check Campaign Budget Campaign Manager Client name + Campaign name Budget surplus CampaignsAdverts Budget Cost

5 5© 2010 Bennett, McRobb and Farmer Elements of DFDs External Entities –People, organizations or systems that the system being modelled communicates with –Rather like actors, except an external entity is not necessarily a direct user of the system –Typically trigger processes Campaign Manager

6 6© 2010 Bennett, McRobb and Farmer Elements of DFDs Processes –Processes that transform data in some way –Named and numbered –Normally require at least one input and produce at least one output –Inputs / outputs (I/O) may flow to or from other processes, data stores or external entities 2.4 Check Campaign Budget

7 7© 2010 Bennett, McRobb and Farmer Elements of DFDs Data Stores –Represent the places where data is stored –Typically files or database tables –In a manual system can represent physical data stores, like card indexes or filing systems Campaigns

8 8© 2010 Bennett, McRobb and Farmer Elements of DFDs Data Flows –Flows of data between: external entities and processes processes and other processes processes and data stores –Can be simple data elements or complex data structures Client name + Campaign name

9 9© 2010 Bennett, McRobb and Farmer Data Dictionaries DFDs are supported by data dictionary entries Each element is defined in a data dictionary –Data elements - name and data type –Data structures - name and composition –Data flows - name and content –Data stores - name and data structures contained –Processes - name and specification of the process, for example in Structured English

10 10© 2010 Bennett, McRobb and Farmer Levels of DFDs Context Diagram –Shows the system and the external entities with which it interacts Top Level Diagram –Shows the main processes in the system - a decomposition of the context diagram process Lower Level Diagrams –Decomposition of the processes in the top level - can be successively decomposed

11 11© 2010 Bennett, McRobb and Farmer Context Diagram Agate Campaign Management System Campaign Manager Client Budget Campaign Staff Campaign Advert Staff Assignment Accountant Concept Note Staff Concept Note Staff Staff Grade Staff Contact Payment Advert Completion Client Contact

12 12© 2010 Bennett, McRobb and Farmer Top Level Diagram (Level 0) 1. Record Clients Campaign Manager Client Staff Assignment Campaign Staff Campaign Advert Accountant Concept Note Staff Concept Note Staff Staff Grade Staff Contact Payment Advert Completion Client Contact 3. Prepare Adverts Notes 6. Browse Concept Notes Concept Note Concept Note 4. Maintain Staff 5. Manage Adverts Advert Contact + Completion Date Clients Client 2. Plan and Manage Campaigns Staff Members Staff Budget Cost Concept Note Campaigns Campaign Staff

13 13© 2010 Bennett, McRobb and Farmer Level 1 Diagram Advert Completion Client Contact 5.1 Set Client Contact Adverts Contact Staff Members Staff Completion Date 5.2 Set Advert Completed

14 14© 2010 Bennett, McRobb and Farmer Data Dictionary Advert Completion = Advert Name + Completion Date Advert Name = Name of advert. Format: X(40) Completion Date = Date on which advert was completed. Format: dd/mm/yyyy.

15 15© 2010 Bennett, McRobb and Farmer Data Dictionary Client Contact = Staff ID + Advert Name Staff = Staff ID + First Name + Last Name + Start Date + Grade + Date Of Birth Staff Members = {Staff} Contact = Staff ID

16 16© 2010 Bennett, McRobb and Farmer Process Definition Process 5.1 Set Client Contact BEGIN FIND Staff in Staff Members with Staff ID that matches Staff ID in Client Contact Contact = Staff ID Write Contact to Adverts using Advert Name END

17 17© 2010 Bennett, McRobb and Farmer Types of DFD In some approaches different kinds of DFD are produced: –Current physical - existing system with physical stores, manual processes and physical descriptions of I/O –Current logical - abstraction of current physical to eliminate the way its done now –Proposed logical - proposed new system

18 18© 2010 Bennett, McRobb and Farmer What DFDs can be used for Modelling existing systems that are to be re-engineered using an object-oriented approach Modelling data flows in systems that do no more than transform data Modelling business processes in existing manual systems Determining the automation boundary for a system (what is to be computerized)

19 19© 2010 Bennett, McRobb and Farmer Why DFDs arent used in O-O In DFDs a clear separation is made between processes and stored data It is assumed that all data is visible to any process that needs to access it In an O-O system the processes that operate on data are the methods of the classes that contain the data as attributes Data is encapsulated within objects, and may be hidden too

20 20© 2010 Bennett, McRobb and Farmer Variations in Notation We have used the notation from Yourdon (1989) because it is the simplest to draw! Alternatives include –Structured Analysis and Design Technique (SADT) –Structured Systems Analysis and Design Method (SSADM)

21 21© 2010 Bennett, McRobb and Farmer SADT 2.4 Check Campaign Budget Campaign Manager Client name + Campaign name Budget surplus Campaigns Adverts Budget Cost

22 22© 2010 Bennett, McRobb and Farmer SSADM 2.4 Check Campaign Budget Campaign Manager Client name + Campaign name Budget surplus D1 Campaigns D2 Adverts Budget Cost

23 23© 2010 Bennett, McRobb and Farmer SSADM SSADM probably has the most complex notation, which we have not covered here, including: –Flows and stores of physical materials –Notation for duplicate elements appearing in the same diagram –Special numbering systems for manual and transient data stores

24 24© 2010 Bennett, McRobb and Farmer Other Structured Techniques In a structured approach, data structures are usually modelled separately in an Entity-Relationship Diagram (ERD), but ERDs dont show processes Entity Life Histories show the events that affect entities over time Structure Diagrams show program structure as a tree hierarchy of modules

25 25© 2010 Bennett, McRobb and Farmer Summary In this presentation you have learned about: What data flow diagrams (DFDs) are What DFDs can be used for Why DFDs are not used in object-oriented analysis and design Variations in notation for DFDs

26 26© 2010 Bennett, McRobb and Farmer References Yourdon (1989) Skidmore, Mills and Farmer (1994) (For full bibliographic details, see Bennett, McRobb and Farmer)


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