Aspects worth to consider from the very beginning:
- In order to maintain the degree of simplicity of the problem this post presents, I haven't provided the exact requirement, on the basis of the bellow E-R diagram was sketched;
- If the given information aren't satisfactory further details will be provided without hesitation;
Given the explanation book 1 delivers:
7.7.4 Placement of Relationship Attributes
The cardinality ratio of a relationship can affect the placement of relationship attributes. Thus, attributes of one-to-one or one-to-many relationship sets can be associated with one of the participating entity sets, rather than with the relationship set..
1.Would you rather prefer to keep the attribute start_date as a relationship attribute or to englobe it in the entity set Congress_Persons?
2.Why?
My answer: I tend to believe that in order to diminish any shadow of doubt that might appear when deciding what is the most representative place to which this attribute belongs, the start_date should be inextricably linked to represents relationship. This way it would explicitly express that the action of taking up a mandate will unarguably come with a start_date.
1 - Database System Concepts Henry F. Korth, S. Sudarshan, Abraham Silberschatz