System Analysis

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System Analysis
System Analysis and Design

• - Mr. Ahmad Al-Ghoul

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Learning Objectives

• Discuss and draw the Lower-Level Diagrams
• Explain how to level and balance a set of data
  flow diagrams
• Explain when to stop leveling
• Explain how to validate the DFDs
• Distinguish between logical and physical DFDs

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Creating a Set of DFDs

• Draw the Lower-Level Diagrams
• Business processes are too complex to be shown on
  a single DFD
• Must use leveling and balancing techniques
• leveling is the process of representing the
  system in a hierarchy of DFD diagrams
• Uses a series of increasingly detailed DFDs to
  describe an information system
• leveling also is called Exploding, partitioning,
  or decomposing
• Child diagrams show a portion of the parent
  diagram in greater detail

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Creating a Set of DFDs

• Draw the Lower-Level Diagrams
• Data flow diagrams are built in layers
• The top level is the Context level
• Each process may explode to a lower level
• The lower level diagram number is the same as the
  parent process number
• Each process on diagram zero may be exploded to
  create a child diagram
• Each process on a lower-level diagram may be
  exploded to create another child diagram
• These diagrams found below Diagram 0 are given
  the same number as the parent process

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Creating a Set of DFDs

• Draw the Lower-Level Diagrams
• Each process is numbered with the parent diagram
  number, a period, and a unique child diagram
  number
• If the parent process has data flow connecting to
  a data store, the child diagram may include the
  data store as well
• A lower-level diagram may contain data stores not
  shown on the parent process

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Creating a Set of DFDs

• Level 1 DFD for process1, shows details of the
  FILL ORDER process in the order system.
• The FILL ORDER consists of three processes,
  VERIFY ORDER, PREPARE REJECT NOTICE, and ASSEMBLE
  ORDER
• Two data stores CUSTOMERS and PRODUCTS
• Depending on the processing logic
• A CUSTOMER submit an ORDER, the VERIFY ORDER
  requires PRODUCT DETAIL from PRODUCTS data store
  and CREDIT STTUS from CUSTOMERS data store, apply
  either REJECTED NOTICE to PREPARE REJECT NOTICE
  process or ACCEPTED ORDER to ASSEMBLE ORDER
  process as output
• If the order rejected, PREPARE REJECT NOTICE
  sends ORDER REJECTED NOTICE to the CUSTOMER
  entity and CREDIT HISTORY to the CUSTOMERS data
  store
• If the order accepted, ASSEMPLE ORDER process
  requires PICKING DETAIL from PRODUCTS data store,
  apply both PICKING LIST to WAREHOUSE entity and
  INVENTORY CHANGE to PRODUCTS data store, as
  outputs

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Creating a Set of DFDs

• Level 1 DFD for process 3, shows details of the
  APPLY PAYMENT process in the order system.
• The APPLY PAYMENT consists of four processes,
  POST PAYMENT, DEPOSIT PAYMENT, PREPARE ACCOUNTING
  ENTERY, and PAY COMMISSION
• Two data stores ACCOUNTS RECEIVABLE and DAILY
  PAYMENTS
• Depending on the processing logic
• A CUSTOMER submit a PAYMENT, the POST PAYMENT
  process requires INVOICE DETAIL from ACCOUNTS
  RECEIVABLE data store, apply both CUSTMER PAYMENT
  to the DAILY PAYMENT data store and PAYMENT
  DETAIL to the ACCOUNTS RECEIVABLE data store as
  outputs
• DEPOSIT PAYMENT requires DAILY PAYMENT from DAILY
  PAYMENTS data store, apply BANK DEPOSIT to the
  BANK entity as output
• PREPARE ACCOUNTING ENTERY requires ACCOUNTING
  PAYMENT from DAILY PAYMENTS data store, apply
  CASH RECEIPT ENTERY as output to the ACCOUNTING
  entity
• PAY COMMISSION requires COMMISSION EARNED from
  POST PAYMENT process, apply COMMISSION as output
  to the SALES REP entity

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Creating a Set of DFDs

• when to stop leveling
• if a process has a single input data flow or a
  single output data flow then it should be
  apparent that there is little point in leveling
  it any further.
• when a process can be accurately described by a
  single active verb with a singular object, this
  also indicates that the level has been carried
  out to a sufficiently low level.
• When you believe that there is a separate process
  for each choice on all lowest-level menu options,
  ask yourself if anything useful will be gained by
  further leveling of a process. Would any more
  detail influence your decisions? If the answer
  is no, then there is little point in taking the
  leveling further.

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Data Flow Diagrams

• Balancing
• involves insuring that information presented at
  one level of a DFD is accurately represented in
  the next level of a DFD.
• DFD level 0 must have the same inputs and outputs
  as context diagram
• Process 1.0, which appears in a level 0 diagram,
  must have the same inputs and outputs when
  decomposed into a level 1 diagram, the same thing
  for the other processes in level o

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Data Flow Diagrams

• Validating the DFD
• Syntax errors
• Assure correct DFD structure
• Semantics errors
• Assure accuracy of DFD relative to actual and
  desired business processes
• User walkthroughs
• Examine lowest level DFDs to ensure consistent
  decomposition
• Examine names carefully to ensure consistent use
  of terms

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Logical Versus Physical DFDs

• While structured analysis tools are used to
  develop a logical model for a new information
  system, such tools also can be used to develop
  physical models of an information system
• Logical data flow diagrams show how the business
  operates
• They have processes that would exist regardless
  of the type of system implemented
• Physical data flow diagrams show how the system
  operates or how the new system will be
  implemented
• Physical data flow diagrams include
• Clarifying which processes are manual and which
  are automated
• Describing processes in greater detail
• Sequencing processes in the order they must be
  executed

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Sequence Summary

• Lower level DFDs show additional detail of the
  information system through the leveling technique
  of numbering and partitioning
• Leveling continues until you reach the the
  functional primitive processes, which are not
  decomposed further
• All diagrams must be balanced to ensure their
  consistency and accuracy

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Sequence Summary

• In this Sequence we have
• Explained how to draw level 1 and the
  Lower-Level Diagrams
• Defined the terms leveling and balancing
• Explained how to level and balance a set of data
  flow diagrams
• Explained when to stop leveling
• Explained how to validate the DFDs
• Distinguish between logical and physical DFDs

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Reference

• 1 System Analysis and Design, Sixth Edition
• Authors Gary B. Shelly, Thomas J. Cashman
  and Harry J. Rosenblatt ,
• Publisher SHELLY CASHMAN SEWIES.
• 2 system analysis and design, sixth edition
• Authors Kenneth E. Kendall and Julie E.
  Kendall
• Publisher Prentice Hall
• 3 Modern Systems Analysis and Design Third
  Edition
• Authors Jeffrey A. Hoffer , Joey F. George,
  Joseph S. Valacich
• Publisher prentice hall
• 4 System Analysis and Design, 3rd Edition
• Authors Dennis, Wixom, Roth
• Publisher John Wiley sons