Data Flow Diagrams(3) by pptfiles

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									Data Flow Diagrams
       S.S.A.D.M.
• S.S.A.D.M. - Structured
  Systems Analysis and
  Design Method
• Uses different techniques
  to model a system
   – Data Flow Diagrams
   – Entity Relational Model
     (Logical Data Stores)
   – Normalisation
 What is a Data Flow
    Diagram?
• Known as DFDs
• A way to model a real
  world situation
• They are the interface
  between the real world
  activities and an
  understanding of how this
  can be converted into a
  computer system.
Why do we use DFDs?
• It is a way of taking the
  physical view and
  converting it into a logical
  view.
• The physical view - all
  documents involved
• The logical view - the data
  they contain
• Their main purpose is to
  communicate with the
  user, the analyst’s
  understanding of the
  scope of the required
  system
        Levelling
• DFDs are expanded or
  decomposed into levels.
• Separating each process
  into sub processes
• Uncovers more and more
  detail
      The Elements
The four main elements of
 DFDs notation
      Data Flows, with a
       label to indicate what
       data is flowing
      Processes, that handle
       the data
      Data stores, within the
       system (diary, filing
       cabinet or computer
       file)
      Outside entities,
       outside sources of
       data
     Process and Data
          Stores
A process is made up of

                                 Destination
                                 (Place or Name)
Process Number



                             Process
                             description Should
                             be descriptive,
                             starting with a
                             verb.
Data Stores

  Can be M for manual             Name of
  or D for computer     M1        Store
  base data stores.
          Outside Entity
Is anything outside the
  system that is of interest to
  the system. Can be a
  person, a company or
  another system.
                 Customer
                      a



 Outside entity shows the
 Name and a lowercase
 alpha character is used to      Customer
                                      a
 uniquely identify it.

                              If an outside entity is
                              repeated for the
                              purpose of neat layout
                              a line is added across
                              the top.
       Data Flow
Is shown by a line with an
  arrowhead, indicating the
  direction of the flow of
  data. Each data flow
  should be named to
  indicate what data is being
  passed. Nouns or
  adjectives only no verbs
  are permitted.
                     The Context Diagram
     You decide which agencies are to be
      part of the system that you are
      examining.
     These agencies fall inside the system
      boundary and are reduced to one box in
      the centre.
     This is a Context Diagram



                           a                                      b
                       Production
                        Planning                              Supplier


                           Production                      Delivery
                                Plan                       Note



      e                                 Stock Control         Supplier Details Update Form
                                                                                                c
                Bill of Materials                                  Delivery Note
    Design                              Maintain              Material Requirements List     Purchasing
                                        Stock System

                                              Stock
                                              Withdrawal
                                              Note


                                            d
                                          Factory



    (Lejk & Deeks)
           Task 1

• Draw a context diagram for
  DVD rental store
   All data flows going into the
    system must be received by a
    process.
   All data flows going out of the
    system must be generated by
    process.
   The first task is therefore to
    identify these processes:
            1       Stock cler k

                    M aintain
                  planned call- off




            2      Stock cler k

                    M aintain
                  stock car ds




            3       Stock cler k

                    Pr epar e
                mater ial r eq mnts
                       list
            Draw the external entities and
                    data stores.



                    1      Stock clerk
    a
                                            M1 Bill of materials
Production                 Maintain
Planning                 planned call-off


                                            M2    Stock cards
   b

Supplier



    c               2 Stock clerk

Factory                    Maintain
                         stock cards




                    3      Stock clerk
        d
                           Prepare
  Purchasing
                        material reqmnts
                              list
            Level 1 Physical DFD - Complete
  Finally draw in the data flows to give a
  completed diagram. Note that a data flow
  must have a process at the end .

                                              1     Stock clerk
    a                                                                B O M details
                      Production
                                                                                            M1 Bill of materials
Production                                           Maintain
Planning                Plan
                                                  planned call-off
                                                                      Planned call-off
                                                                       details               M2      Stock cards
    b

Supplier
                              Delivery note                          Stock details


    c                                         2 Stock clerk

Factory                                              Maintain
                      Stock                       stock cards
                      withdrawal note
                                                                                     Stock details
                   Updated
             supply details

                                Delivery      3     Stock clerk
        d                       note
                                                   Prepare
  Purchasing         Material requirements     material reqmnts
                             list                     list
                     )skeeD & kjeL(
               Hairdressing Salon Level 1
                     Physical DFD
                                                1    Receptionist
                                                                                             New client
                                                      Register                                   details
                                                    Appointment
                                                                                Existing client
                 Appointment                                                               details
                      details                                                                              M1 Client card index
                                 Confirmation
                                 Request                              Appointment
                                                                              details
                                           Confirmation
                                          Details
                                                                                     M2 Appointment diary

                                                                        Confirmation of
        a
                                                                               arrival
      Client               Appointment
                                details         2    Receptionist

                                                     Confirm                  Appointment              Change of
                                                      arrival                      details
                                                                                                     hairstyle etc.



                   Change of
                    hairstyle etc.
                                                3   Hairdres s er/Rc ptns t
                     (Lejk & Deeks)
                                                      Conduct
                                                     appointment




(Lejk & Deeks)
           Task 2

• Draw a level 1 DFD for DVD
  rental store
           Process 3 Level 2


                  3   Hair/Reception

Client
a Clie
  a                     3.1      Hairdresser
                                               Appointment Details
                        Conduct Appointment
   Hair Details                                   M2        Diary



                        3.2      Hairdresser

                        Inform Reception


                                                 Change of Hair Details


                       3.3     Receptionist

                       Complete Appointment        M3        Client Card
            Task 3

• Draw a series of level 2 DFDs
  for DVD rental store
             Task 4

• For the following scenario
  create a context diagram &
  L1&2 DFDs

• A hotel needs you to create the
  following systems:
  – Customer booking
  – Allocating rooms
  – Billing customers and creating an
    invoice

								
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