Tutorial 6
DFDs vs. Use Case Diagrams
(Textbook Chapter 7 & Appendix)
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
1
Learning Objectives

Practice more DFDs

Practice more Use Case Diagrams

Understand commonalities and differences
between the two types of diagrams
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
2
Part 1
Ch. 7 Ex. 12 and Ch. 7 App, Ex. 1

Consider the following narrative:

Tutorial 6
Maximum Software is a developer and supplier of software products
to individuals and businesses. As part of their operations, Maximum
provides a help desk line for software purchased form Maximum. An
operator enquires about the nature of incoming calls. Calls that do
not require help desk functions are directed to other company units.
Help desk consultants are organised by product. The operator
directs the call to a consultant skilled on the software that the caller
needs help with. Some calls need to be put on a queue. Once a
consultant answers the call, the consultant determines if this is the
first call from this customer. If so, the consultant creates a new call
report to keep track of all information about the problem. If it is not
the first call about a problem, the consultant asks the customer
about the call report number and retrieves the open call report to
determine the status of the enquiry.
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Ch. 7 Ex. 14 and Ch. 7 App, Ex. 1 (cont.)
If the caller does not know the call report number, the consultant
collects other identifying information such as caller’s name, the
software involved etc in order to conduct a search for the appropriate
call report. If a resolution of the customer’s problem has been found,
the consultant informs the client as to what the resolution is, indicates
on the report that the customer has been notified, and closes out the
report. If resolution has not been discovered, the consultant finds out
if the consultant handling this problem is on duty and if so, the call is
transferred to that consultant, who records any new information from
the client. For new and continuing problems, the consultant tries to
find the solution by using the relevant software and looking up
information in reference manuals. If the consultant knows how to
solve the problem, he / she tells the customer how to deal with the
problem and closes the report. Else the consultant files the report for
continued research and tells the customer that someone at Maximum
software will get back to him / her and if the customer discovers new
information he / she should call quoting the report number.
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
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Ch. 7 Ex. 12 and Ch. 7 App, Ex. 1 (cont.)

Decisions to make

What is to be represented, i.e. what level of detail
to show?
Keep Level-0 DFD uncluttered, 7-9 processes
(max). DFD can be subsequently further
decomposed. Unless further information becomes
available, assumptions may be necessary to
further decompose.
Tutorial 6
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Ch. 7 Ex. 12 and Ch. 7 App, Ex. 1 (cont.)

Decisions to make (cont.)
 What
is part of the system and what is an
external entity / agent?
One option is to consider the processes
performed by the consultants and operators as
sub-systems within the system rather than as
external entities (sources/sinks). This adds detail;
however, it allows bottlenecks in these processes
to be corrected. So, it depends on the scope of
the problem (and what the client wants to pay for)
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
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Ch. 7 Ex. 12 and Ch. 7 App, Ex. 1 (cont.)
Call
Enquiry on Nature of Call
0
Non-Help
Desk Call
Nature of Call
Client
Call Report # or Other Data
New Problem Data
Help Desk
System
Other
Unit
Interim Problem Status
Final Call Resolution
Help Desk System Context Data Flow Diagram
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
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Ch. 7 Ex. 12 and Ch. 7 App, Ex. 1 (cont.)

Decisions to make (cont.)

Decision logic is not shown on the DFDs. How do
we cope with that?
a) show the data flows in / out of processes that
correspond to all possible decisions
b) simulate some rudimentary decision logic on
the DFDs
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
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Option a)
1.0
ill
ed
U
In nfil
fo led
Re O
sp rd
on er
se
If the Order is not filled,
then the doctor is contacted.
The doctor responds …etc etc
Hospital Pharmacy
Partial Level-0 Diagram
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O
rd Prescription
er
In
fo
Information necessary
to make the decision
Pharmacy
Tech Review
D1 Patient File
o
U
nf
Review &
Send
Prescription
to Station
2.0
Review
Prescription
Order by
Station
tie
nt
In
f
Prescription
Pa
Doctor
Order Info
3.0
Fill
Order
© 2008 Prentice Hall, Ovidiu Noran
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Option b)
E.g.: “…the consultant determines if this is the first call from this
customer. If so, the consultant creates a new call report […]. If it is not
the first call about a problem, the consultant […] retrieves the open
call report to determine the status of the enquiry.
3.0
5.0
Previous Call
Information
Determine
problem
status
Determine
if first call
First Call
Information
Call Report
4.0
Call Report
Create
Call Report
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Information
D1 Call Report File
© 2008 Prentice Hall, Ovidiu Noran
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New Problem Data
Call
1
Receive
Call
Enquiryon
onNature
Natureof
ofCall
Call
Inquiry
D1
Call Queue
H elp Desk
Call Information
Non-Help
Desk Call
Information
Previous
Call
Information
Determine
if First
Call
New
Information
on Problem
Closed Call
Indication
5
3
Close
Call
Report
Closed Call Problem
Resolution
Help Desk
Call Information
2
9
Final Call Resolution
Nature of Call
Call
Information
Determine
Direction
of Call
Call Report # or Other Data
Client
Determine
Problem
Status
8
Research
Problem
Call
Report
First Call
Information
Open Call
Information
D2
Call Report File
4
Other
Unit
Create
Call
Report
Problem
Information
Call Report
Information
D1
Call Queue
6
Transfer
Call
Problem
Data
New
Problem
Data
7
Open Call
Information
Record
New
Information
Interim Problem Status
Tutorial 6
© 2008 Prentice
Hall, Ovidiu
Noran
Help Desk System
Level-0
Data
Flow Diagram
11
Place Call
Direct
the Call
Operator
Answer Call
Customer
Retrieve
problem
report
Knowledge
base lookup
Consultant
Refer
to original
consultant
Update
call report
Close
call report
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Help Desk System
Use
Diagram
© 2008 Prentice
Hall,Case
Ovidiu Noran
12

Can this system be improved?

A customer may have to explain their problem
and/or question over and over to multiple people:
an operator and possibly several consultants.
Has this happened to you?

Why not let the initial operator have access to
the customer problem database so that the caller
is handed off to a consultant and the customer’s
already opened problem file goes along with him.
Does this happen in the GU system ?
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
13

Can this system be improved? (cont.)

The operator could have sufficient information
and the option to direct the call to the proper
consultant.

Clients could call the assigned consultant directly
on follow-up calls to an initial call for help.

Why should clients not be called back by
consultants with updates on the problem or the
resolution, rather than the client having to call
back to check?
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
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
Can this system be improved? (cont.)
General areas of improvement for DFDs are:

processes that simply collect and pass on
information rather than transforming data

collecting the same information into several
processes

placing untransformed data into data stores thus
causing unknown delays in processing this data

cycles or loops that have no apparent
termination.
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
15

Same Observations as in previous tutorial:

There is substantially less detail on the use case
diagram than in the narrative

The missing detail will be completed when writing
the use cases at intermediate and detailed levels.

Decision logic is not shown on the Use Case
diagrams. It is described in the written Use Cases
and/or Activity Diagrams and/or Sequence
Diagrams (the latter can also show timing)
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
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Part 2
Case Study: Pine Valley Furniture (PVF)

Review the Case Study DFD and the
‘corresponding’ Use Case Diagram
described in Tutorial Wk 5
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
17
Tutorial 6
Level-0 data flow
diagram
for
theNoran
PVF WebStore
© 2008
Prentice Hall,
Ovidiu
18
Case Study: PVF (cont.):
Model the functionality of Pine Valley
Furniture Webstore Application with a use
case diagram.
 Six high-level functions identified to be
included in the use case diagram.
 The functions represent the “work” or
“action” parts of the Website.

Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
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Case Study: PVF (cont.):
Browse
Catalog
Maintain
Account
Customer
Login
Shipping
Clerk
Place Order
Fill Order
Check Order
Tutorial 6
WebStore
use case diagram
© 2008 Prentice Hall, Ovidiu Noran
20
Case Study: PVF (cont.):

The functionality should now be further
detailed using written use cases as shown
in the lecture. E.g. for the Place Order use
case:
Place Order Brief Description
Customer connects to PVF WebStore and links to Order page. System checks customer
information and creates a new order. Customer searches catalog, adds items / makes
changes to the order, checks out assisted by the system. Customer requests payment
screen, makes payment assisted by system. System sends e-mail confirmation and
finalizes order.
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
21
Case Study: PVF (cont.):

Possible Intermediate level description:
PVF
Tutorial 6
Source:
(Satzinger
al.,
©
2008 Prentice
Hall, OvidiuetNoran
2008)
22
Case Study: PVF (cont.):

Possible fully developed description – adds
triggering event, actors, related use cases,
stakeholders and pre- and post-conditions:
PVF
Tutorial 6
Source:
(Satzinger
al.,
©
2008 Prentice
Hall, OvidiuetNoran
2008)
23
Case Study: PVF (cont.):

Possible fully developed description (cont.):
PVF
Tutorial 6
Source: (Satzinger et al., 2008)
© 2008 Prentice Hall, Ovidiu Noran
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Summary

In this tutorial you learned how to:

Practice DFDs

Practice Use case Diagrams

Understand commonalities and differences
between the two types of diagrams
Tutorial 6
© 2008 Prentice Hall, Ovidiu Noran
25