The original two relationships between Instrument and Party were adequate to explain the basic structure of Instrument. It quickly became apparent, though, that there could be more than one banker in and more than one customer in an Agreement, so the relationship is really “many-to-many”, requiring, in each case, an “intersect entity class” to describe each occurrence of one Party (for example) being the banker in one Instrument. Rather than a separate intersect entity class for each kind of relationship, Figure 20-5 shows a single Banking Role as a sub-type of the more general concept Agreement Role. This allows an unlimited number of Parties to play roles in an unlimited number of Agreements. Specifically, an Agreement Role is the fact ...

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