Data, Processes, and Events: Keys to Comprehensive Analysis - High-Performance Web Databases: Design, Development, and Deployment - page 48

Exhibit 4-1. Entity-life history diagram.
COURSE supports the relationship that INSTRUCTOR has with COURSE.
This type of entity-life stage is called a relationship support stage.
Therefore, each stage in an ELH must either support the entity or a rela-
tionship that the entity has with another entity. By understanding the dif-
ferences between entity-support and relationship-support stages, a sys-
tems analyst can better understand the nature of relationships in data
models. For example, a stage is an entity-support stage only if its event
does not involve another entity; if another entity is involved, the stage is a
relationship-support stage.
ELH AND PROCESS MODELING
Each stage of life of an entity is represented by one or more functions in
a process model. A function may not equal a single process in the process
model. The correspondence of functions to processes in the process model
depends on the degree of abstraction with which the process model was
developed. The degree to which there is one-to-one correspondence, how-
ever, is not critical during early analysis.
An important practice in analyzing life stages is that in addition to iden-
tifying the specific functionality required, analysts must also identify the
events required to change the entity's state. A number of different analyti-
cal tools are available for the analysis of events. The most popular is the
State-Transition Diagram. Although they effectively model events and
states, State-Transition Diagram have little connection to data flow and
entity relationship diagrams.
Exhibit 4-2. Sample of a partial entity-relationship diagram.