a)

Correspondences between ER Model and Relational Model Constructs:

1. Entity Sets:

   • Correspondence: An entity set in the ER model maps to a relation (table) in the relational model.
   • Mapping: Each entity set becomes a table in the relational model, with each entity becoming a row, and attributes becoming columns.

2. Relationships:

   • Correspondence: Relationships in the ER model can be represented using foreign keys in the relational model.
   • Mapping: Relationships become associations between tables, and foreign keys are used to establish the connections between related entities.

3. Attributes:

   • Correspondence: Attributes in the ER model map to columns in the relational model.
   • Mapping: Each attribute becomes a column in the corresponding relation.

4. Keys:

   • Correspondence: Keys in the ER model are mapped to primary keys in the relational model.
   • Mapping: The primary key of a relation uniquely identifies each row in the table, just as a key in the ER model uniquely identifies each entity.

Alternative Mappings:

• In some cases, an ER construct can have multiple possible mappings to the relational model. For example, a multi-valued attribute in the ER model can be represented as a separate relation with a foreign key relationship to the original entity, or as a composite attribute in the entity's table.

b)

Options for Mapping EER Model Constructs to Relations:

1. Inheritance Hierarchies:

   • Option: Each subclass can be mapped to a separate relation with a foreign key referencing the superclass.
   • Conditions: This option works well when each subclass has distinct attributes and when queries need to access subclass-specific attributes individually.

2. Aggregation:

   • Option: Aggregated objects can be mapped to separate relations, with foreign keys linking them to the main relation.
   • Conditions: This option is useful when complex objects are aggregated into higher-level entities and when queries need to access the aggregated objects separately.

3. Specialization/Generalization:

   • Option: Specialized entities can be mapped to separate relations with a foreign key referencing the generalized entity.
   • Conditions: This option is suitable when specialized entities have additional attributes or relationships specific to their specialization, and when queries need to access specialization-specific attributes individually.

4. Union Types:

   • Option: Union types can be represented as separate relations, each representing a possible option in the union.
   • Conditions: This option is applicable when entities can have multiple types and when queries need to access attributes specific to each type.

The choice of mapping options depends on the specific requirements of the application, the nature of the data model, and the desired querying and performance characteristics. The selected mapping should accurately represent the semantics of the EER model while ensuring efficient storage, retrieval, and manipulation of data in the relational model.