When reviewing the ER exercise models for our project, I was confused about when cardinalities and relationships had to be indicated between different entities - especially associative entities. It seems that relationships are described at the designer's discretion and is therefore an necessary portion of database design. The descriptions (ie talks with, is a, etc.) therefore only clarify relationships existing between entities.
For cardinalities, it is inconsistent whether or not they are outlined or not. In ER exercise #2 only some cardinalities are completely outlined (ie customer and sales person) while the others have only one pair of cardinalities if any at all. What is the significane, if any, of these missing cardinalities.
A member of my group said that this left the relationship ambiguous but does this have any implimication as to the nature of their relationship and their effect on the actual database structure?
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