07a : Worked Example
7a Generic DFD functions
One of the ways in which to develop detailed DFD models for a proposed system
is to utilise generic DFD function models. The generic LOGIN function was
introduced in section 3. Produce the DFD - TOP LEVEL for LOGIN
Login Function – Context Diagram
ASCENT FILES
genLOGIN.ASC
Terms of Reference
Statement of Purpose:
Requirements:
Login Function
A generic login function
1. allow users to login
2. obtain forgotten password
3. validate login
4. register new user
Context Diagram Description
A user may login to the system by providing the userid and password. These details
are validated against a user list. Valid users are granted access rights and invalid users
are notified. Users may request a forgotten password which is emailed to the users
registered email address. New users may apply for a userid and password.
Context Diagram : LOGIN
Events List:
1. User submits userid and password
2. user request password (forgotten)
3. New user registration
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Section 07 – Worked Solution
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07a: Worked Solution
SOLUTION:
DFD Top Level : LOGIN (generic)
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Section 07 – Worked Solution
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07b : Worked Example
7b The Example Library
Background:
The aim of the library is to provide for its members a high quality book loan service.
A member may join and leave the library. Whilst a member a person may loan and
renew books. A book reservation may be made and cancelled. Before leaving, the
member must return any outstanding loans and cancel any reservations. The library
manager obtains books from a small group of specialist suppliers. The manager can
also remove books from the library, these are often given away to local charities. An
automated information system is required to improve efficiency. In the first instance
it should be limited to dealing with membership, book stock and recording details of
reservations and loans.
Statement of Purpose:
The purpose of the Example Library System (ELS) is to handle all of the customer
services and book control functions of the library. It is expected to give an improved
desk service to customers and enable more efficient stock management.
Tasks:
1.
2.
3.
4.
Draft a Context Diagram and Events list.
Draft the Top-Level DFD
Apply leveling to derive Low-Level DFDs
Explosion each of the Process’s as a result of levelling down:
You will now have the following systems models:
1.
2.
3.
4.
Context Diagram
Events List
Top-Level DFD
Low-Level DFDs
Mansha Nawaz
Section 07 – Worked Solution
3
07b : Worked Solution
7b The Example Library
Background:
The aim of the library is to provide for its members a high quality book loan service.
A member may join and leave the library. Whilst a member a person may loan and
renew books. A book reservation may be made and cancelled. Before leaving, the
member must return any outstanding loans and cancel any reservations. Books are
obtained by the library manager from a small group of specialist suppliers. The
manager can also remove books from the library, these are often given away to local
charities. An automated information system is required to improve efficiency. In the
first instance it should be limited to dealing with membership, book stock and
recording details of reservations and loans.
Statement of Purpose:
The purpose of the Example Library System (ELS) is to handle all of the customer
services and book control functions of the library. It is expected to give an improved
desk service to customers and enable more efficient stock management.
Context Diagram:
Mansha Nawaz
Section 07 – Worked Solution
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Event List:
1.
2.
3.
4.
5.
6.
7.
8.
9.
new member joins
member changes details
member leaves
member loans book
member returns book
member reserves book
member cancels reservation
new books arrive
manager deletes books
DFD fragments:
a
Customer
newCust
1
add
member
member
1 members
2
change
member
member
1 members
memberInfo
a
Customer
changedCust
member
1 members
3 loans
a
Customer
3
delete
member
oldCust
outLoan
Mansha Nawaz
Section 07 – Worked Solution
loan
2 reservations
5
reservation
1 members
a
Customer
4
add
reservation
resInfo
member
reservation
book
a
Customer
5
cancel
reservation reservation
resInfo
2 reservations
4 books
2 reservations
1 members
member
3 loans
a
Customer
newLoan
6
add
loan
loan
reservation 2 reservations
a
Customer
b
Supplier
c
Manager
Mansha Nawaz
oldLoan
7
cancel
loan
loan
3
loans
newBook
8
add
book
book
4
books
oldBook
9
delete
book
book
4
books
Section 07 – Worked Solution
6
DFD: First Draft
1
a
5
add
newCust
Customer
2
member
cancel
reservations
reservation
resInfo
reservation
memberInfo
a
member
oldCust
Customer
changedCust
1
2
members
member
member
4
resInfo
change
add
member
reservation
3
member
delete
member
book
outLoan
b
reservation
2
reservations
4
books
Supplier
reservation
loan
7
book
cancel
loan
loan
3
newBook
loans
reservation
book
9
loan
oldLoan
8
delete
add
book
book
6
a
add
c
Customer
loan
Manager
oldBook
newLoan
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Section 07 – Worked Solution
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Top-Level DFD as a result of Levelling up:
custInfo
a
1
Customer
member
1*
memberInfo
members
2*
update
members
a
update
reservations
resInfo
membercheck
Customer
outLoan
reservation
book
reservation
memreservationcheck
4
books
bookcheck
2
reservations
4
books
loancheck
3
loans
book
bookreservationcheck
b
loan
4*
bookInfo
Supplier
update
books
reservation
3*
loanInfo
update
loans
bookInfo
1
membercheck
Mansha Nawaz
c
members
Section 07 – Worked Solution
Manager
8
Explosion of Process 1 Update Members as a result of levelling down:
1 update members
1.1
a
add
member
custInfo
Customer
a
memberInfo
Customer
custInfo
1.2
change
member
member
member
custInfo
1
members
member
2
reservations
memreservationcheck
1.3
delete
member
a
outLoan
Customer
loancheck
3
reservation
loans
4
books
book
2
reservations
Similar explosions of the other leveled processes would be drawn
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Section 07 – Worked Solution
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