Chapter 7: Problem 2

Discuss the options for mapping EER model constructs to relations

Short Answer

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The mapping from EER models to relations involves transforming entities into tables, attributes into columns, and relationships into separate tables or via foreign keys. Hierarchies or categories can be mapped using methods like the single-table method, the class-table method, or the concrete-table method.

Step by step solution

Mapping Basic and Composite Attributes

In the EER model, entities and relationships can have basic attributes. Each basic attribute can be mapped to a column in a relational table. Also, composite attributes, those that can be divided into smaller sub-parts, can be mapped by creating a new column for each component of the attribute. This results in a flat relational structure.

Mapping Entities

Each entity type in the EER model can be mapped as a relational table in the database. This table's primary key is directly inherited from the entity's key attribute. If an entity type has any non-key attributes, these are mapped to adopted columns of the new relational table.

Mapping Relationships

Each relationship in the EER model can be seen as a separate table. The key for this table is a combination of the keys of the participating entities – this is referred to as a composite key. Additionally, any attributes of the relationship are added to the table as regular columns. If relationships are optional or have cardinality, these details can often be implemented through nullability of the fields in a table or through foreign key constraints.

Mapping Hierarchies and Categories

Each superclass/subclass hierarchy or category from the EER model can be mapped using one of three methods: the single-table method, the class-table method, or the concrete-table method. The optimal method depends on various factors such as whether subclasses have many additional attributes or relationships beyond those of the superclass, and whether instances can be part of multiple subclasses.

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Discuss the options for mapping EER model constructs to relations

Short Answer

Step by step solution

Mapping Basic and Composite Attributes

Mapping Entities

Mapping Relationships

Mapping Hierarchies and Categories

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