Review Questions

1
Review Questions
What are the four symbols on a data flow diagram?

• The four symbols on a data flow diagram are
• Rounded rectangles (processes)
• Squares (external agents)
• Open-ended boxes (data stores)
• Arrows (data flows)

2
Review Questions
Every process must have several things. What are
they and why?
Processes describe only one business activity.
Every process must have at least one input data
flow and must produce at least one output data
flow. Generally, there is no reason for a process
to exist if no outputs are produced, and at least
one input is required in order to produce output
3
Review Questions
What is process decomposition and what role does
it play in process modelling?
Process decomposition is when a system is
separated into its component subsystems, which
in turn are decomposed into smaller subsystems,
until such a time as we have identified
manageable subsets of the overall system In
process modeling, decomposition allows you to
partition a system into logical subsets of
processes for improved communication, analysis,
and design
4
Review Questions
What is the parent process for process 3.2.1?
4.3.2.3? And 1.2?
The parent process for 3.2.1 is process 3.2.
The parent process for 4.3.2.3 is process 4.3.2.
The parent process for 1.2 is process 1.
5
Decomposition Diagrams

• A decomposition diagram or hierarchy chart shows
  the top-down, functional decomposition of a
  system.

6
Review Questions
Explain the difference between a syntax error and
a semantics error. Which is usually the most
difficult to find and fix? Why?
A syntax error is an error in the data flow
diagrams that is the result of violating the
rules of data flow diagramming, much like a
grammatical error. A
semantics error is an error of meaning in the
data flow diagram, in which the model does not
accurately represent the business process being
modeled. Semantic errors are harder to detect
because a good understanding of the business
system is required to find them and fix them.
7
Review Questions
8
Review Questions
What are some guidelines for designing a Context
data flow diagram?

• Start by placing a single process symbol in the
  center of the page. The symbol represents the
  entire information system, and you identify it as
  process 0
• Then place the external agents around the
  perimeter of the page and use data flows to
  connect the entities to the central process
• Do not show any data stores in a context diagram
  because data stores are internal to the system
• Place the external agents around the central
  process and label them
• Create labeled input and output data flows
  between the external agents and the central
  system

9
Review Questions
10
Review Questions
What are some guidelines for designing a diagram
0?

• A context diagram provides the most general view
  of an information system
• Diagram 0 zoom in on the context diagram and
  shows major processes, data flows and data
  stores.
• Each process in diagram 0 has a reference number.
• Diagram 0 also represents the external agents and
  data flows that appear in the context diagram

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Review Questions
12
Review Questions
What is balancing?
Balancing involves assuring that all the
information from a higher-level diagram is
appropriately represented on the next level, or
'child' diagram. The child diagram shows more
detail, but must show all the inflows and
outflows to and from the parent process on the
higher level diagram
13
Review Questions
What is balancing?
14
Review Questions
What is the relationship between a context
diagram and diagram 0, and which symbol is not
used in a context diagram?
The context diagram contains only one process
symbol, process 0, which represents the entire
system. Diagram 0 is a more detailed version of
process 0 on the context diagram. The major
processes, data flows, and data stores for the
information system are shown on diagram 0. The
data store symbol is not used in a context
diagram. Use a data store only when two or more
processes use that data store. Otherwise, the
data store is internal to a process, and not
visible from the outside. Because a context
diagram involves only one process, all data
stores are internal to that process and do not
appear in the context diagram
15
Review Questions
The purpose of the plant science information
system is to document the study results from a
wide variety of experiments performed on selected
plants. A study is initiated by a researcher who
submits a research proposal. After a panel
review by a group of scientists, the researcher
is required to submit a research plan and
schedule. A FDA research permit request is sent
to the Food and Drug Administration, which sends
back a research permit. As the experiment
progresses, the researcher fills out and submits
experiment notes. At the conclusion of the
project, the researchers results are reported on
an experiment histogram. Draw a context data
flow diagram
16
Review Questions
A Video Store (AVS) runs a series of fairly
standard video stores. Before a video can be put
on the shelf, it must be catalogued and entered
into the video database. Every CUSTOMER must have
a valid AVS customer card to rent a video.
CUSTOMERS rent videos for 3 days at a time. Every
time a CUSTOMER rents a video, the system must
ensure that he or she does not have any overdue
videos. If so, the overdue videos must be
returned and an overdue fee must be paid before
the customer can rent more videos. Likewise, if
the customer has returned overdue videos but has
not paid the overdue fee, the fee must be paid
before new videos can be rented. Every morning
the store MANGER prints a report that lists
overdue videos if a video is 2 or more days
overdue, the manager calls the customer to remind
him or her to return the video. If a video is
returned in damage condition, the manager removes
it from the video database and may sometimes
charge the customer. SUPPLIER provides video
descriptive information to the system.
17
Review Questions
18
One more example of context diagram
19
One more example of diagram 0
20
Yesterday Lecture

• Process is an organised set of activities which
  transforms inputs to outputs
• Data flow A path for data to move from one part
  of the system to another
• Data store Represents data that is retained for
  later processing
• External entity/agent Represents a person,
  organization, or other system that provides data
  or receives output from the system
• Context data flow diagram Top-level view that
  shows the systems boundaries and scope
• Diagram 0 Diagram 0 zoom in on the context
  diagram and shows major processes, data flows and
  data stores