Hp Integrity NonStop J-Series Bedienungsanleitung PDF herunterladen (Seite 236)

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101

Sample Project-Tracking System

Identifying Relationships Between Classes of Data

The relationship between the "events" data and the "employs" data

is even more complex. An event can have many employees and an

employee can have many events. Thus, the relationship between

these two classes of data is many-to-many (or M:M).

Figure 12-5 shows a diagram of these relationships.

S5044-060

Projects

Events

Employs

Figure 12-5. Relationships Between Instances of Classes of Data

To summarize, the relationships shown in Figure 12-5 are:

One project has one manager 1:1

One project has many events 1:M Each event has one

project

One event can have many employees M:M One employee can

have many events

Depending upon the type of relationship, the following rules may

apply:

• With the exception of items involved in more than one

relationship, data items that belong to classes with a

one-to-one relationship can often be merged into a single

class. Since the "employs" data is also related to the

"events" class, the "projects" and "employs" data should not

be merged.

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