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System Analysis and Design
System Analysis
- Mr. Ahmad Al-Ghoul
Learning Objectives
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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
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Draw the Lower-Level Diagrams
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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
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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
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Draw the Lower-Level Diagrams
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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
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Draw the Lower-Level Diagrams
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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
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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
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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
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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
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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
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Balancing
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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
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Validating the DFD
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Syntax errors
 Assure correct DFD structure
Semantics errors
 Assure accuracy of DFD relative to actual and
desired business processes
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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
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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
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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
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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
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In this Sequence we have
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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
Avicenna
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