Purchase Order Context Diagram by rvr11980

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									Systems Documentation Techniques
     Professor Merle Martin
      Professor Yan Xiong
      College of Business
        CSU Sacramento
 Why Document System
 Data Flow Diagrams

 Flowcharts

 Difference between DFDs and
Why Document Systems?
 User confidence that you understand
 Successive refinement of detail down
  to programming level
 Ease of Program Maintenance,
  System Modification, Reengineering,
  and Replacement
Why Document Systems?
   Problem Solving
   Humans solve complex
    problems by
    breaking them into smaller and
      smaller modules
    until they fit into the human mind
    solving the modular sub-problems
    aggregating small solutions
      into total solution
 Why Document Accounting
  Information Systems
 Data Flow Diagrams (DFDs)

 Flowcharts

 Difference between DFD
Data Flow Diagrams
 Data flow diagram (DFD)
  graphically describes flow
  of data within any system
 Used to document existing systems
  and to plan and design new ones
 No ideal way to develop a DFD
    judgment within standard rules
Data Flow Diagrams
   DFD composed of only four elements:
   Data sources and destinations: External Entities
      Another organization/organization unit which
       exchanges data with the focal system
      A person who interacts with the system
       (customer of a banking system)
      Another information system
   Data Flows
   Processes
   Data Stores: Temporary or permanent
    repository of data
DFD Symbols
 INPUT         PROCESS            OUTPUT

External   Data         Data      External
 Entity    Flow         Flow       Entity
Source                              Sink
 DFD Symbols

           Payment 1.1      deposit
Customer         Process                 Bank
Source                                   Sink
                     Remittance data
Data Flow Diagrams Explosion
 Data flow diagrams
  subdivided into successively
  lower levels in order to provide
  increasing amounts of detail
 This decomposition process is
  called “explosion”
Data Flow Diagram Explosion
 Context Level
 Ist Level Explosion

 2nd Level Explosion

 Succeeding levels as necessary

 Until reach primitive level

    Ready to code
Context Diagram
   Includes only
     External Entities
     Data Flows
   All elements included on Context
    Diagram must be included
    somewhere on lower level diagrams
   Data stores rarely included!
Context Diagram
 Why discourage Data Stores on
  Context Diagram?
   Author includes them
 Context Diagram shows interaction
  of your system with outside world
 Data Stores are INSIDE your system,
  not in outside world
          Purchase                Purchase
Inventory Requisition              Order          Vendor

  Order                 Purcha-                   Receiving
 System    Special       sing      Purchase
           Order                    Order

          Context Diagram
1st Level Explosion
 Also includes all data
  flows and external entities
 Now data stores are added

 Excellent means of confirming
  understanding of system between
  analyst and client
 Each process will be exploded into
  lower level DFDs
 Ist Level Explosion
            Purchase                              Inventory
                           Order                   Problem
                                Approved            Orders
 Order                         2 Order
 Entry                     Set Ship
  Vendor             Draft P.O
            P.O. Copy       Prepare   P.O.Noti-   Receiving
                              P.O.    fication
2nd and Succeeding
   Must be consistent with
    parent DFD
     Same external entities
     Same data stores
     Same data flows
2nd Level Explosion
(Process 1)
                                 Logged-in      Inventory

 Order                      1.2 Order
 Entry                      Edit                Problem
                           Order                 Orders
  Log-in              Edited
    #s                Order
                            1.3                    Process
                          Approve    Approved        2.1
                           Order      Order
DFD Rules -- Process
A. No process can have only outputs (a
B. No process can have only inputs (a
  black hole)
C. Verb phrase labels
   DFD Rules -- Data Store
D. Data cannot move directly from one data store
  to another data store -- it must be moved by a
E. Data cannot move directly from an outside
  source to a data store -- it must be moved by a
F. Data cannot move directly to an outside sink
  from a data store -- it must be moved by a
G. Noun phrase label
DFD Rules -- Source / Sink
H.   Data cannot move directly from a
     source to a sink. It must be moved
     by a process.
I.   Noun phrase label
DFD Rules -- Data Flow
J. A data flow has only one direction of flow
  between symbols; a data flow may flow in
  both directions to and from a data store
  (usually two symbols)
K. A fork in a data flow means that exactly
  the same data goes to two different
  processes or data stores.
DFD Rules -- Data Flow
L. A data flow cannot go directly back
  to the same process it leaves
M. A data flow to a data store means
  update (delete or change)
N. A data flow from a data store means
  retrieve or use
O.Noun phrase label
Other DFD Issues
   Two additional guidelines
     Inputs  to a process are different from outputs
      of that process
     Every process in a DFD has a unique name
Draw a Context Diagram and a 1st level explosion
Current System Description for the payroll system at No-Wear Products.
    Time data are recorded in each department using time cards and
    The time data are sent to the payroll by different departments.
    Payroll clerks review the time data for their completeness.
    Human resources send the payroll data on personnel changes, such
     as increases in pay rates and new employees.
    Payroll clerks update the payroll file based on these changes.
    At the end of the period, payroll clerks enter the time card data into
     the payroll file for processing. The payroll supervisor reviews the file
     and makes necessary corrections.
    Payroll clerks send the direct payments to the bank and also the
     direct deposit slips to the departments.
 Why Document Accounting
  Information Systems
 Data Flow Diagrams

 Flowchart

 Difference between DFD and
   A flowchart is an analytical technique
    used to describe some aspect of an
    information system in a clear,
    concise, and logical manner.
   Flowcharts use a standard set of
    symbols to pictorially describe
    transaction processing procedures.
Flowchart Symbols
   Flowcharting symbols can be divided
    into the following four categories:
     1 Input/output symbols
     2 Processing symbols
     3 Storage symbols
     4 Flow and miscellaneous symbols
Flowcharting Symbols:
Input Output Symbols
Symbol            Name

               Online keying

 Flowchart Symbols:
 Processing symbols
Symbol         Name

              Manual operations

              Computer processing

              Auxiliary operation
    Flowchart Symbols:
    Storage Symbols
Symbol            Name

                 Magnetic disk

                 Magnetic tape
Flowchart Symbols: Flow and
miscellaneous Symbols
Symbol    Name

          Document or processing flow
          On-page connector

          Off-page connector


What are Document Flowcharts?
     A document flowchart illustrates the flow
      of documents and information between
      areas of responsibility within an
     A document flowchart is particularly
      useful in analyzing the adequacy of
      control procedures.
     Flowcharts that describe and evaluate
      internal controls are often referred to as
      internal control flowcharts.
What are Computer
System Flowcharts?
    System flowcharts depict the
     relationship among the input,
     processing, and output of an AIS.
    A system flowchart begins by
     identifying both the inputs that enter
     the system and their origins.
    The input is followed by the
     processing portion of the flowchart.
What are Computer
System Flowcharts?
   The resulting new information is the
    output component.
   System flowcharts are an important
    tool of system analysis, design, and
What are Computer
System Flowcharts?

  Storage      Process

What are Program Flowcharts?
   A program flowchart describes the
    specific logic to perform a process
    shown on a systems flowchart.
   A flow line connects the symbols and
    indicates the sequence of operations.
   The processing symbol represents a
    data movement or arithmetic
What are Program Flowcharts?
             Input data

        If a condition is met   No

         Perform calculation

           Update record
What are Program Flowcharts?
    The input/output symbol represents either
     reading of input or writing of output.
    The decision symbol represents a
     comparison of one or more variables and
     the transfer of flow to alternative logic
    All points where the flow begins or ends
     are represented by the terminal symbol.
Flowchart for Processing
Credit Orders
Start      sales

         Approved      No   Reject
         for credit?        order


         Inventory     No   Back-
         available?         order


         Fill order         Stop
   The Dewey Construction Company processes its
    payroll transactions to update both its payroll master
    file and its work-in-process master file in the same
    computer run. Both the payroll master file and the
    work-in-process master file are maintained on disk and
    accessed directly.
    Data to be input to this system are keyed onto a tape
    using a key-to-tape encoder. This tape is then
    processed to update the files. This processing run also
    produces a payroll register on magnetic tape,
    employee paychecks and earnings statements, and a
    printed report listing error transactions and summary
    Prepare a system flowchart of the process described.
 Why Document Accounting
  Information Systems
 Data Flow Diagrams

 Flowchart

 Difference between DFD and
Differences Between DFDs and
   DFDs emphasize the flow of data and
    what is happening in a system,
    whereas a flowchart emphasizes the
    flow of documents or records
    containing data.
   A DFD represents the logical flow of
    data, whereas a flowchart represents
    the physical flow of data.
Differences Between DFDs and
   Flowcharts are used primarily to
    document existing systems.
    DFDs, in contrast, are primarily used
    in the design of new systems and do
    not concern themselves with the
    physical devices used to process,
    store, and transform data.

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