Systems Documentation Techniques

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Systems Documentation Techniques

• Professor Merle Martin
• Professor Yan Xiong
• College of Business
• CSU Sacramento
• 2/6/023

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Agenda

• Why Document System
• Data Flow Diagrams
• Flowcharts
• Difference between DFDs and Flowcharts

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Why Document Systems?

• User confidence that you understand system
• Successive refinement of detail down to
  programming level
• Ease of Program Maintenance, System Modification,
  Reengineering, and Replacement

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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

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Agenda

• Why Document Accounting Information
  Systems
• Data Flow Diagrams (DFDs)
• Flowcharts
• Difference between DFD

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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

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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

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DFD Symbols
INPUT
PROCESS
OUTPUT
Process
Data Flow
Data Flow
External Entity
External Entity
Source
Sink
Data Flow
Data Store
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DFD Symbols
1.1 Process Payment
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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

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Data Flow Diagram Explosion

• Context Level
• Ist Level Explosion
• 2nd Level Explosion
• Succeeding levels as necessary
• Until reach primitive level
• Ready to code

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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!

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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

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0 Purcha- sing
Context Diagram
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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

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Ist Level Explosion
Inventory
Status
1 Edit Order
Problems
Special Order
Problem Orders
Approved Order
2 Set Ship Mode
Purchase Order
Info
Vendor
Draft P.O
3 Prepare P.O.
P.Order
P.O.Noti- fication
P.O. Copy
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2nd and Succeeding Levels

• Must be consistent with parent
  DFD
• Same external entities
• Same data stores
• Same data flows

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2nd Level Explosion (Process 1)
Purchase Requisition
1.1 Log-in Order
Inventory
Special Order
Inventory
Logged-in Order
Order Entry
1.2 Edit Order
Status
Next
Problem Orders
Problems
Log-in s
Edited Order
1.3 Approve Order
Process 2.1
Approved Order
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DFD Rules -- Process

• A. No process can have only outputs (a miracle)
• B. No process can have only inputs (a black hole)
• C. Verb phrase labels

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DFD Rules -- Data Store

• D. Data cannot move directly from one data store
  to another data store -- it must be moved by a
  process.
• E. Data cannot move directly from an outside
  source to a data store -- it must be moved by a
  process.
• F. Data cannot move directly to an outside sink
  from a data store -- it must be moved by a
  process.
• G. Noun phrase label

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DFD Rules -- Source / Sink

• Data cannot move directly from a source to a
  sink. It must be moved by a process.
• Noun phrase label

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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.

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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

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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

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Exercise

• 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 clocks.
• 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.

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Agenda

• Why Document Accounting Information
  Systems
• Data Flow Diagrams
• Flowchart
• Difference between DFD and Flowchart

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Flowcharts

• 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.

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Flowchart Symbols

• Flowcharting symbols can be divided into the
  following four categories
• Input/output symbols
• Processing symbols
• Storage symbols
• Flow and miscellaneous symbols

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Flowcharting Symbols Input Output Symbols
Symbol
Name
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Flowchart Symbols Processing symbols

Symbol
Name
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Flowchart Symbols Storage Symbols
Symbol
Name
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Flowchart Symbols Flow and miscellaneous Symbols
Name
Symbol
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What are Document Flowcharts?

• A document flowchart illustrates the flow of
  documents and information between areas of
  responsibility within an organization.
• 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.

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What are ComputerSystem 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.

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What are ComputerSystem Flowcharts?

• The resulting new information is the output
  component.
• System flowcharts are an important tool of system
  analysis, design, and evaluation.

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What are ComputerSystem Flowcharts?
Input
Process
Storage
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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 calculation.

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What are Program Flowcharts?
Input data
No
Yes
Perform calculation
Update record
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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 paths.
• All points where the flow begins or ends are
  represented by the terminal symbol.

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Flowchart for ProcessingCredit Orders
Enter sales order
Reject order
No
Yes
Back- order
No
Yes
Fill order
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Example-Flowcharts

• 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 information.
• Prepare a system flowchart of the process
  described.

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Agenda

• Why Document Accounting Information
  Systems
• Data Flow Diagrams
• Flowchart
• Difference between DFD and Flowchart

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Differences Between DFDs and Flowcharts

• 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.

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Differences Between DFDs and Flowcharts

• 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.