Databases Reference
In-Depth Information
Chapter 4
Data, Processes,
and Events: Keys to
Comprehensive
Analysis
Philip Friedlander
E
-
VENT
DRIVEN
ANALYSIS
CAN
ADD
AN
EXTRA
DEGREE
OF
RIGOR
TO
BOTH
DATA
AND
FUNCTIONAL
MODELING
AS
WELL
AS
TO
THE
PROCESS
OF
SYS-
.
TEMS
Event-driven analysis expands both the requirements
gathering and requirements validation processes and introduces addi-
tional levels of depth and rigor to data, process, and event modeling tech-
niques. This chapter introduces modeling tools that combine process,
data, and event techniques.
ANALYSIS
ENTITY-LIFE HISTORIES AND DATA MODELING
Entity-life history (ELH) diagrams show all the events in the life of an
entity; that is, all the states in which the entity can exist during its life.
Each major data entity in the data model should have an ELH diagram that
shows the major stages of its existence. However, more information than
the stages of an entity's life are needed for a thorough understanding of
the entity.
Most entities have certain required states (e.g., creation or instantiation,
updating, and deletion). Exhibit 1 shows an ELH diagram for an entity
called INSTRUCTOR. It has the required create, update, and delete stages.
These stages are called the entity support stages, because these stages are
required to support the entity's existence.
Exhibit 1 also shows an additional life stage, ASSIGN INSTRUCTOR TO
CLASS. If this life stage does not support the entity, what is its purpose?
The partial entity-relationship diagram (ERD) in Exhibit 2 shows that
INSTRUCTOR teaches COURSE. The life stage of ASSIGN INSTRUCTOR TO
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