Please help me answer these questions related to databases. Also, provide an exp

Question

Please help me answer these questions related to databases. Also, provide an explanation for your answer.

1. When would it be wise to specify the role played by an entity in a relationship? a) when the same entity set participates more than once in the relationship set, b) when the . relationship is ternary, or c) when the entity represents an abstract rather than physical thing ______

2. In an ER model, would it be possible for the same two entity sets to participate in two different relationship sets? (yes/no) _________

3. It is possible for a attribute to be multivalued in a ___________________ but not a _________________. (Fill in the blanks to get the best possible answer that can be formed using the terms ‘ER model’, ‘relational schema’, and ‘recursive relationship’.)

4. Why might you want to model ‘address’ as a composite attribute (built from attributes ‘street’, ‘city’, ‘state’, and ‘zip’, perhaps) rather than just using all of the individual attributes? Would it be a) because in the model we might want to sometimes refer to the address as a whole and sometimes to parts of the address, b) to save space, or c) to avoid possible null values ______

5. Why might it be a bad idea to model the name of an instructor’s department as an attribute of the instructor? Would it be because: a) we might in the future want to allow instructors to belong to multiple departments, b) it is important to model the smallest possible number of attributes, or c) department names can change? (select all that apply) _________

Explanation / Answer

1. When same entity participates more than once in a relationship, then it is wise to specify the role played by entity in a relationship.

For ex:

If Supervises is a relation between same entity employee then it would be wise to specify that first employee takes role of supervisor and second employee takes role of employee as worker.

2.

In ER diagram, same 2 entities can participate in two different relationship sets. True

For ex:

Take 2entities Employee and Department.

2relationship between them can be : works_for i.e. employee works for which department

manages i.e. which employee manages which department

3.

It is possible for a attribute to be multivalued in a ER model but not in a recursive relationship.

Recursive relationship: If an entity participates more than once in a relationship then that relationship is known as recursive relationship.

4.

We model 'address' as a composite attribute because in the model we might want to sometimes refer to address as a whole and sometimes to the parts of address.

Also, it can also be the case that sometimes in address we need state before city or zip first followed by street ,city etc. This is possible when we make 'address' as composite attribute.

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