DFDs vs. Use Case Diagrams

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• Tutorial 6
• DFDs vs. Use Case Diagrams
• (Textbook Chapter 7 Appendix)

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Learning Objectives

• Practice more DFDs
• Practice more Use Case Diagrams
• Understand commonalities and differences between
  the two types of diagrams

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Part 1
Ch. 7 Ex. 12 and Ch. 7 App, Ex. 1

• Consider the following narrative

• 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 callers name, the software
involved etc in order to conduct a search for the
appropriate call report. If a resolution of the
customers 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.
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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.

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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)

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Ch. 7 Ex. 12 and Ch. 7 App, Ex. 1 (cont.)
Help Desk System Context Data Flow Diagram
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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
  decisionsb) simulate some rudimentary decision
  logic on the DFDs

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Option a)
Information necessary to make the decision
If the Order is not filled, then the doctor is
contacted.
The doctor responds etc etc
Hospital PharmacyPartial Level-0 Diagram
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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.
5.0
Previous Call Information
Determine problem status
First Call Information
Call Report
Call Report Information
D1
Call Report File
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New Problem Data

Call



1

Enquiry on Nature of Call

Inquiry on Nature of Call

Call Report or Other Data

Client

9

Receive

Final Call Resolution

Nature of Call

Call

Close

Call

Report

D1
Call Queue

Call

Closed Call Problem

New
Information

Resolution

Help Desk

Information
Call Information

Closed Call

on Problem

2

Indication

5

8

Determine

3

Previous

Determine

Direction

Research

H
elp Desk

Call

Problem

Determine

of Call

Problem

Call Information

Information

Status

if First

Call

Call

Non
-
Help

Report

Desk Call

Problem

First Call

Open Call

Information

Data

Information

Information

Call Report File

D2

4

New

Other

Problem

Create

Call Report

Unit

Call Queue

D1
Data

Call

Information

6

Report


7


Transfer

Open CallInformation
Record

Call

Problem

New

Information

Information

Interim Problem Status

Help Desk System Level-0 Data Flow Diagram
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Place Call

Directthe Call
Operator
Answer Call
Customer
ltltincludesgtgt
ltltincludesgtgt
Knowledgebase lookup
Retrieveproblem report
Consultant
Refer to original consultant
Update call report
ltltextendsgtgt
Close call report
Help Desk System Use Case Diagram
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• 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 customers
  already opened problem file goes along with him.
  Does this happen in the GU system ?

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• 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?

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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.

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• 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)

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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

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Level-0 data flow diagram for the PVF WebStore
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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.

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Case Study PVF (cont.)
WebStore use case diagram
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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.
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Case Study PVF (cont.)

• Possible Intermediate level description

PVF
Source (Satzinger et al., 2008)
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Case Study PVF (cont.)

• Possible fully developed description adds
  triggering event, actors, related use cases,
  stakeholders and pre- and post-conditions

PVF
Source (Satzinger et al., 2008)
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Case Study PVF (cont.)

• Possible fully developed description (cont.)

PVF
Source (Satzinger et al., 2008)
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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