Information Technology Reference
In-Depth Information
ways. An entity-relationship diagram, such as the one shown in Figure 12.18a, describes a
number of objects and the ways they are associated. An ER diagram (or any other modeling
tool) cannot by itself fully describe a business problem or solution because it lacks descriptions
of the related activities. It is, however, a good place to start because it describes object types
and attributes about which data might need to be collected for processing.
Figure 12.18
a
Data and Activity Modeling
(a) An entity-relationship diagram.
(b) A data-flow diagram. (c) A
semantic description of the
business process.
(Source: G. Lawrence Sanders, Data
Modeling, Boyd & Fraser
Publishing, Danvers, MA: 1995.)
MID
MEMBER
PLAY
GOLF
DATE
PAID
NAME
ADDRESS
DATE
TIME
SCORE
b
PROCESS
SYMBOL
ENTITY SYMBOL
DATA-FLOW LINE
DATA-FLOW LINE
DATA STORE
Tee time
Available times
Assign
tee time
MEMBER
Schedule
Reservation request
Group information
Course access
Check
member in
MEMBER
Member Card
Member ID
Date
Sort
scores
Scores
MEMBER
Score card
Score card
Calculate
handicap
Handicap
Tee time
c
To play golf at the course, you must first pay a fee to become a member of the golf club. Members are
issued member cards and are assigned member ID numbers. To reserve a tee time (a time to play golf),
a member calls the club house at the golf course and arranges an available time slot with the reception
clerk. The reception clerk reserves the tee time by writing the member's name and number of players
in the group on the course schedule. When a member arrives at the course, he or she checks in at the
reception desk where the reception clerk checks the course schedule and notes the date on the
member's card. After a round of golf has been completed, the members leave their score card with
the reception clerk. Member scores are tracked and member handicaps are updated on a monthly basis.
Activity Modeling
To fully describe a business problem or solution, the related objects, associations, and activ-
ities must be described. Activities in this sense are events or items that are necessary to fulfill
the business relationship or that can be associated with the business relationship in a mean-
ingful way.
