Context Diagrams / DFD’s
Note: Please check additional files for the diagrams
The description of a proposed system to support the ordering of takeaway food follows:
“Fush & Chups” wants to install a system to record orders for fish and chips. When regular
customers call “Fush & Chups” on the phone, their phone number goes automatically into the
ordering system. The phone number invokes the name, address, and last order date comes
automatically up on the screen. Once the order is taken, the total, including tax and delivery, is
calculated. Then the order is given to the cook. A receipt is printed. Occasionally, special offers
(coupons) are printed so the customer can get a discount. Drivers who make deliveries give
customers a copy of the receipt and coupon (if any). Weekly totals are kept for comparison with last
Your task is to develop a context diagram and a Level 0 DFD for the fish & chips ordering system.
You may make some assumptions as necessary but remember you are modelling what it likely an
incomplete understanding of the system.
2. You are the project team leader in a software production company that is developing an insurance
claims system for a client insurance company. One of your team members submits a Level 0 DFD
(shown below) for the system.
(please check attachment for the system)
Inspecting this DFD, but leaving aside the question of how well it may represent the actual
process of dealing with insurance claims, you realize that your team member has broken
several of the rules for constructing DFDs. In what ways is the diagram incorrect?
b. Using your own understanding of how insurance claims are handled, develop a corrected
version of your team member’s Level 0 DFD. You may add new processes, data flows and
data stores (but not external entities) as necessary. Make sure you keep all the existing
processes, data flows, external entities and the data store even though you may modify,
rearrange, reconnect or relocate them in various ways to produce your corrected diagram.
c. Construct a context diagram that is consistent with your answer to part b above.
[adapted from a problem in George M. Marakas, Systems Analysis and Design: An Active
Approach, Prentice-Hall (2001)]
3. You are on a team of analysts working on a system to support student enrolment applications for an
educational institution. The team, including you, has developed a Level 0 DFD (shown below using
the Yourdon/De Marco DFD notation) for the system.
a. You realize that your team has omitted the important step of creating a context diagram for
the system before starting work on the Level 0 DFD. Construct a context diagram for the
system that is consistent with this Level 0 DFD.
b. The following is an informal description of process 2 “Process Application”. Use it to develop
a Level 1 DFD for process 2.
After an application has been checked, the entry criteria for the course(s) that the student
has applied to enrol in are retrieved from the course details file and the application is
assessed to see whether the student satisfies all of the required criteria. If one or more of the
relevant entry criteria are not satisfied, the application is unacceptable, and is rejected. If the
application satisfies the entry criteria, the availability of places is checked. To do this, the
maximum enrolment for the course is retrieved from the course details file, and current
enrolments in the course are retrieved from the enrolments file. If the number of current
enrolments is less than the maximum for the course, the application is accepted and a
notification sent to the relevant College Office. If the applied for course is full, the application
is marked “wait listed”, which means it is placed in a waiting list in case an already accepted