This chapter examines several pitfalls which the designers and users of a conceptual model
must take care to avoid. In each case the problem arises because of a misinterpretation of
the meaning of certain relationships. The term connection trap will be used to describe any
such interpretation error; the terms fan trap and chasm trap will be applied to particular
cases to indicate the cause of the problem. Any conceptual model will contain potential
connection traps. Many of these may be of no signiﬁcance to the enterprise; others can be
avoided by restructuring the conceptual model. Either way, their existence must be
recognised so that they can be eliminated or else given a clean bill of health. We will start
with some trivial cases, and progress to those that are rather less obvious.
The meaning of any relationship type must be carefully deﬁned, and thoroughly
understood, in order to avoid errors of misinterpretation. For example, the relationship
Tutors in Fig. 11.1 could refer to subject-tutorship, personal-tutorship, or both of these.
Fig. 11.1 What does Tutors mean? Subject-tutorship? Personal-tutorship? Both of these?
An error in the interpretation of the meaning may cause the database to be incapable of
storing certain information (e.g. personal as distinct from subject tutorships), or may
mean that information retrieved from the database is interpreted incorrectly (e.g. a list
of tutors might be interpreted as being a list of personal tutors when it is actually a list
of subject tutors).
The above entity-relationship structure can represent: