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DOMAIN MODELING OF OBJECT-ORIENTED INFORMATION SYSTEMS 153
The Women’s Senior team from club Flippers for event Beam in meet Town Invitational
receives the score of 41.5. (Sentence A)

This sentence forms a meaningful unit of information. Note that in order to talk about the score
of 41.5, we need to include the other four data items (italicized in sentence A). For example, it is
obvious that we cannot omit the club’s name from this sentence; if we do that, we get a meaning-
less sentence. To derive a fact type from sentence A, we note that 41.5 is the score that a team
receives for an event. That is, the fact type is of the form:

Team ( ) . . . receives Score ( ) . . . for Event ( ) . . . (Sentence B)

In the context provided by sentence A, we can see clearly what we mean by a “team”: a “team”
is “a team from a club for a competition type in a meet.” Therefore, it is identified by the combina-
tion of the club’s name, competition type’s name, and the meet’s name. And similarly, an event
is identified by a combination of the meet’s name, the competition type’s name, and event type’s
name. Adding the reference scheme to sentence B, we have the fact type (with informal notation
being used for reference schemes):

Team (club name + competition type name + meet name) . . . receives Score (number)
. . .
for Event (meet name + competition type name + event type name) . . . (Sentence C)

It is conceptually clearer to write the above fact type (sentence C) using the following “non-
standard” format in which square brackets are used to denote the reference schemes of the entity
types they enclose:

Team ([Club] + [Competition Type] + [Meet]) . . . receives Score (number) . . . for
Event ([Meet] + [Competition Type] + [Event Type]) . . . (Sentence D)

As a validity check, we note that sentence A can be rewritten in the format of sentence D as
the sentence E below, which contains precisely the same information:
Team identified by Club Name “Flippers” and Competition Type Name “Women’s
Senior Team” and Meet Name “Town Invitational” receives Score of 41.5 for Event
identified by Meet Name “Town Invitational” and Competition Type Name “Women’s
Senior Team” and Event Type Name “Beam.” (Sentence E)

(Note: In the above sentence, there is an important constraint regarding the Competition Type
Name and Meet Name. The same values for them should appear as part of the identification of
both the Team and the Event. This situation is sometimes known as “derived redundancy.” The
constraint can be formally expressed if desired. Perhaps more important, in implementing any use
case that involves the creation of facts of these fact types, we need to ensure that the constraints
are satisfied. As far as the single fact type D is concerned, we can eliminate the redundancy using
an objectified relationship. In doing so, however, concepts such as “team” may not be represented
explicitly, which generally is not a desirable outcome.)
The key to the above analysis is actually sentence A. It provides a “context” in which we can