Transcript Process Modelling - Information Management and Systems

CSE1204 - Information Systems 1
Process Modelling
Using Data Flow Diagrams –
Building and Levelling Them;
Process Modelling Using Function
Decomposition
Example system:

a generic warehouse-inventory information system
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Levelling Data Flow Diagrams
any "real" system is too large to represent as
single data flow diagram

a
the solution is to decompose the system into a
hierarchy of levels of processing
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the process model of the system then consists of a
set of levelled data flow diagrams

levelling of DFDs improves their readability and
usefulness as a communication tool

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Levelling of DFDs
Levelling creates a hierarchical decomposition
of the processing within the system

Context diagram

Level 0 diagram
Level
1 diagrams
 Level
2 diagrams
.
.
.
 Level n diagrams
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Context Diagram
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the highest level data flow diagram is the context diagram
the context diagram shows the interaction of the system
with its environment in terms of data flows
the context diagram defines the boundary of the system
(the scope of the system)
only the data flows which leave the system and the data flows which
come from outside the system are shown
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Context Diagram

the entire system is represented as a single process
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all external agents (sources and sinks) are shown
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no data stores are shown: they are inside the boundary
of the system
EASY GO
HOTEL
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Example Context Diagram
sales order
Sales Order
System
purchase order
Suppliers
goods returned
goods unavailable
notice
shipping slip
supplier delivery
Inventory
System
checked supplier
invoice
Warehouse
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Accounts
Department
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Level Zero Diagram
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the level zero data flow diagram is the diagram at
the level immediately below the context diagram
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it "expands" the single process on the context
diagram to show the major, high-level processes (or
functions) within the system
1.0
4.0
2.0
3.0
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Level Zero Diagram

all external agents (sources and sinks) are
included because the level zero diagram,
like the context diagram, represents the
entire system
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the number of each process ends in .0
which corresponds to the level of the
diagram:
e.g.
1.0, 2.0, 3.0 etc.
often just 1, 2, 3 etc. are used
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Example Level Zero Diagram
Order Entry
System
purchase order
Suppliers
sales order
2.0
Monitor
Stock
levels
3.0
1.0
out of stock
notice
Fill
Sales
Orders
Accept
Deliveries
supplier
delivery
Stock file
shipping slip
Warehouse
checked supplier
invoice
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Accounts
Department
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Levelling DFDs
Context diagram
1
2
3
1.1
Level zero diagram
1.2
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Diagram
1 (at Level 1)
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Level 1 diagrams
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a set of data flow diagrams is created at Level 1
there is one Level 1 diagram for each of the processes
at Level zero
each diagram decomposes a Level zero process into
several processes
2.4
2.1
2.3
2.5
2.2
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Level 1 and lower level diagrams
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each Level 1 diagram and diagrams at lower
levels (e.g. Level 2, Level 3) show only a part of
the processing
Level 1 processes are numbered 1.1, 1.2, 1.3,
and 2.1, 2.2, 2.3 etc
that part is shown in more detail than on the
Level zero diagram
no external agents are shown on a Level 1 or
lower diagrams, as the entire system is not
being represented
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Example Level zero diagram
SUPPLIERS
CUSTOMERS
p.o.
number
Customer details
Product
details
product qty
1
Record and
Invoice
Sales
customer
invoice
product
holding
INVENTORY
product
delivered
qty
product product holding
order qty
SALES ORDERS
product
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order qty
product
p.o. invoice
order
qty
2
Maintain
Product
Inventory
delivery
qty
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Example Level 1 diagram
Check
Stock Available
1.1
Check
Customer
Credit
Product
details
product
qty
customer credit
status
SALES ORDERS
product
product
holding
INVOICES
available qty
1.4
1.3
product
qty
INVENTORY
1.2
Customer
details
Create Sales
Invoice
Record
Sales
Demand
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customer
invoice
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Levelling of DFDs
Context
Level 0
Level 1
Level 2
1
1.1
1.2
2
1.3
2.1
3
2.2
3.1
1.1.1 1.1.2
4
3.2
3.2.1
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4.1
4.2
4.3
3.2.2
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References
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WHITTEN, J.L., BENTLEY, L.D. and DITTMAN, K.C. (2001) 5th
ed., Systems Analysis and Design Methods, Irwin/McGraw-HilI,
New York, NY. Chapters 8
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HOFFER, J.A., GEORGE, J.F. and VALACICH (2005) 4th ed.,
Modern Systems Analysis and Design, Benjamin/Cummings,
Massachusetts.
Chapter 7
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