Data Flow Diagram for Employees and Staff Personal Information System by kmz12675

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									                Systems Analysis and Design




                      Data Flow Diagrams
                            Development




29 April 2003      31T4/IT52 Commercial Systems Development   1




                                 Aims

• To consider possible ways to develop data flow
  diagrams
• To identify problems with data flow diagrams
• To see extensions of data flow diagrams to include
  control elements as control flow diagrams
• To describe control in terms of state transition
  systems




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                Developing data flow diagrams

• No fixed rules about how to develop a data flow
  diagram in a given situation
• At best, we can suggest methods dependent on the
  particular situation
• Complication since there is no one DFD for each
  situation
   – if the DFDs of two individuals are identical then some
      replication has taken place
   – two analysts working independently may choose the
      same external entities, the same data stores, and same
      data items entering the system
• A DFD is complete only when it feels right (Always
  ask a friend!)
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                  Developing DFDs (cont’d)

• Generally, diagrams are developed by iterating
  between levels
• Remember that a DFD is meant to produce enough
  material for a clear program specification to be
  extracted
• The novice should complete the SSADM cycle to
  determine that right level of detail is reached




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                Direct data flow diagramming
• Favoured by experienced analysts but has no
  apparent rules to use
• Starting with data stores (static) since these do not
  identify processes; starting with external entities
  difficult since the system boundaries are not
  determined
   – start with large blank sheet of paper
   – put discovered data stores somewhere in middle
   – try to identify some high level processes and throw into
      middle
   – insert data flows, via processes, between data stores and
      external entities
   – review situation and redraw diagram with corrections

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     Direct data flow diagramming (cont’d)
• Remember: trying to create a model that gives an
  overview and a detailed breakdown at the same time
   – need whole picture to start detecting the detail and the
     detail to appreciate the whole picture
• For the expert all this is feasible; for the beginner it is
  generally hopeless!
• For any real system there are
     – documents flowing around (Document Flow Diagram)
     – products and resources moving to and fro (Resource Flow
       Diagram)
     – places where things happen, for which certain people in the
       company hierarchy are responsible (Organisation Chart)
     – these diagrams and charts are not official SSADM but help in
       starting development of DFD
     – each of these diagrams/charts help identify system boundary
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                       Document Flow Diagram

• Consider a hairdressing Salon where proprietor deals
  with most situations single-handedly
• To expand business from current two shops, over a
  wide geographical distribution, required good control
  of all documents
• So, identify as many documents as possible
   – for each, need its source and its recipient
   – may be done by observation of current practice
   – may include:
           • invoices/delivery notes from suppliers to
             stock clerk; adverts from marketing to
             magazines; daily training records from
             personnel to training agencies; payments
             from accounts to suppliers, etc.
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                                                                Document Flow Diagram
                              Supplier




                                                     Invoice
                  Payments                     Delivery                      Marketing
                                                 Note



                                                                                         Adverts
                                   Checked                      Stock
       Accounts                    Invoices                    Control



                                                                                               Magazine
                                                                                               s


                                              Personnel
         P60



                             P45                                                 Reference
                                               Training
                                               Records            Training
                                                                  Records

      Employee



                                              Appointments


                                                                                   Agency




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                                                               System Boundary?
                             Supplier




                                                     Invoice
                 Payments                     Delivery                    Marketing
                                                Note




                                                                                      Adverts
                                  Checked                    Stock
      Accounts                    Invoices                  Control



                                                                                            Magazine
                                                                                            s


                                             Personnel
         P60



                            P45                                               Reference
                                              Training
                                              Records          Training
                                                               Records

     Employee



                                             Appointments


                                                                               Agency




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                       Document Flow Diagram

• Determine what’s inside and what’s outside system,
  i.e., determine boundary
   – for Salon, Supplier, Magazines, and Training Agency
      outside
   – proprietor decides Accounting and Marketing outside
• Unclear how orders are made: seems to be by
  telephone, for instance, since no document is raised
  to go to supplier
• Appointments are made with a Customer; Customer
  telephones and Appointment logged in Appointments
  Book (not a ‘moving’ document)
• Now use this Document Flow Diagram to form DFD

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                                   Salon Context Diagram


    Supplier                                                                                                             Agency
                                               Invoice                       Reference
                        Delivery
                          Note                                                                         Training
                                                                                                        Records
                                                                       Salon
    Payment


                          Checked Invoice                                                     P45


  Accounts                                                                                                          Employee



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                      Level 1 Current System DFD

      Supplier                                                                                                       Agency


                        Delivery Note
                                                                                                       Reference
                                           1

                                                    Receive                             4
                                                   Delivery
                                                              *                             Consider
                                                                                            Employee
                     Invoice                                                                                *

                                                                                                                                      Employee
                                                                         Delivery
                                                                  M1
                                                                          Notes



                               2                                                                                             P45

                                   Reconcile
                                    Invoice
                                                                  M3     Employee                       5
                                               *                          Files
                                                                                                            Terminate
                 Checked Invoice                                                                            Employment
                                                                                                                         *



     Accounts

                                                                  3
                                                                                                 Training
                                                                         Train                   Records                           Agency
                                                                       Employee
                                                                                    *




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Resource Flow Diagram: stock item, employee/trainee

                   Supplier                                       Buy
                                                                 Stock

     a)

              Use                                Remove                                          Store
             Stock                                Stock                                          Stock




                 Register                                   Participate in
                Employee                                    Appointment


     b)


                                                              Terminate
                                                             Employment

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                     Level 1 Current System DFD


                                                                                                Personal
                      Order                                                                      Details
     d                          1                                     3


  Supplier                           Buy                                  Consider                                  Employee
                                    Stock                                 Employee
                                             *                                       *         Termination
                Delivery Note



                                                 Stock            Employee
                                      M2                    M3
                                                  File              Files
                                                                                         Reference




                        a                            2

                     Customer         Bill           Participate in                                        Agency
                                                      Appointment
                                                                  *




   29 April 2003                31T4/IT52 Commercial Systems Development                                              14
                          Organisation Chart


                                                Proprietor




                                                                            employ staff
                                                Manager (1)                 order stock
                                                                            reconcile deliveries




   Receptionist                                  Stylist                          Trainee
       (1+1)                                      (4+3)                            (3+3)




set-up appointments                                participate in appointments
monitor training                                   use stock

   29 April 2003                     31T4/IT52 Commercial Systems Development                                            15




               Level 1 Current System DFD
      a                   1     Reception                          4    Manager

   Customer   Request            Set Up                                 Order
                              Appointment                               Stock
                                            *                                     *
                                                        Employee
                                                   M3    Files                        Order
                          M3 Appointments

                                                                                                                 d

                                                                   M4     Order
                                                                           Book                               Supplier

                          2     Stylist            M2    Stock                        Invoice
                                                          File

   Agency                      Monitor
                               Training
                                            *

                                                                   5    Manager

              Reference                                 Employee                              Delivery Note
                                                   M3    Files          Recieve
                                                                         Stock
                                                                                  *

                          3 Manager
              Personal
  Employee     Details          Employ
                                 Staff             M5   Invoice
                                                        Ledger
                                            *




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                Data Flow Diagrams: Problems?

• List any difficulties with the use of Data Flow
  Diagrams




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                        Vending Machine
• Requirements: machine must do the following:
     – Accept objects from customer in payment of purchase
     – Check each object to ensure it is not a “slug”: done by validating
       size, weight, thickness, and serrated edges
     – Accepts only 10p, 20p, 50p, £1: other coins treated as false and
       returned to customer
     – Only initiate payment computation or product selection process
       after valid coin is detected: the system must be difficult for people
       to trick
     – Accept product selection from customer
     – Check to see whether selected product is available (check product
       dispenser to ensure not empty), and if not available then return
       coins automatically and notify the customer




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                 Vending Machine (cont’d)
     – Accept a variety of products, which will change from time to time:
       hence, as a maintenance feature, the product prices should be
       changeable
     – Return customer’s payment on request
     – Dispense product to customer if it is available and amount
       sufficient
     – Return correct change to customer if amount deposited is greater
       than the product price
     – Disable product selection after product is dispensed and until the
       next validated coin is received
     – Make deposited coins available for change




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                               Summary

• In this lecture, we have looked at ways and means of
  developing data flow diagrams for the current system
• These include Direct and Formal development
  approaches
• Considered very briefly the problem of control in data
  flow diagrams




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                                         Example

• This example comes from Pressman (1987), p.p.
  169-172, based on Zave (1982)
• Initial problem statement:
   – Patient Monitoring System:
           • … monitors the vital signs of all patients
             in a ward, maintains records by updating a
             patient log, notifies nursing staff if
             anything goes awry, and produces a patient
             report upon request.




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                 Step 0: Conceptual System Model



                         patient                      reader                RTC




       nurse

                                                                monitor

                         display


                                                                          database

                                                 terminal handler
       doctor




                Environment                              Target system




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                Step 1: Fundamental System Model
                     Context Diagram: level 0



                                                                      Nurse
          Patient

                         Vital signs                  Report


                                         Patient             Warning message
                                        monitoring
                                         system

                        Request for                                 data
                          report
                                               Log data
           Nurse
                                                                           Log
                                                                           data




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      Step 2: Identify functions to be performed

• First refinement step exhibits FOUR major functions:
   – local monitoring
   – central monitoring
   – patient log update
   – report generation
           • and an internal data structure emerges:
                  – (a file) holding ‘patient bounds’




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  Step 3: Identify information flow, data stores,
                 external entities
                    DFD: level 1

                                   1                                                    Patient
          Patient    Vital signs
                                                            Patient data                bounds
                                         Local
                                       monitoring                        Vital signs
                                                    *
                                                        2

                                                             Central
                         Warning message                    monitoring
           Nurse                                                         *
                                                                    Formatted
                         Report                                    patient data

                                          3                                   4

                                               Report                             Updat
                                              generator                            log
                    Request for
                      report                                *                               *
           Nurse

                                                        Log data             Log data




                                                                         Log
                                                                         data




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           Step 4: Refine, Abstract                                      Validate

• Particular refinement of the central monitoring
  process:
           • … the patient’s vital data are unpacked
             and compared with bounding values for
             vital signs. Bound violations result in a
             warning message.




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                                                    Step 4 (cont’d)
                                                      DFD: level2

1

      Local
    monitoring               2      Central monitoring                                                                Patient
                 *   Patient data                              Temperature                                            bounds
                                     2.1                                     2.2
                                                                                                    Vital signs
                                           Unpack            Pulse              Evaluate             bounds
                                                                                 bounds
                                            signs
                                                                                violation
                                                    *                                        *                    4
                                                         Blood pressure
                                                                                                                        Updat
                                                                                                                         log
                                                                             Blood pressure,                                    *
                                                                             temp and pulse
                                     2.3                   signal warning                         Formatted
    Nurse                               Produce                                                  patient data
                                        warning
                                        message
                                                    *                        2.4
      Warning message                                                              Format
                                                                                   patient
                                                                                    data                                Clock
                                                                                             *
                                                                                                     Date, time




    29 April 2003                           31T4/IT52 Commercial Systems Development                                     27




                                                    Step 4 (cont’d)

    • Observations:
       – continuity of information is maintained
       – a new source (clock) ‘emerges’




    29 April 2003                           31T4/IT52 Commercial Systems Development                                     28

								
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