Midterm Flashcards
What is EER (Enhanced Entity-Relationship) in database modeling?
EER (Enhanced Entity-Relationship) is an extension of the Entity-Relationship (ER) model that includes additional modeling concepts like specialization/generalization, category (union type), and aggregation, making it more expressive and capable of representing more complex real-world scenarios.
What does ‘cardinality’ refer to in the context of the EER model?
Cardinality refers to the number of instances of one entity that can be associated with instances of another entity. It specifies the numeric relationships between occurrences of entities. Examples of cardinality constraints are one-to-one (1:1), one-to-many (1:M), and many-to-many (M:N).
Define ‘specialization’ in the EER model.
Specialization is a process of defining a set of subclasses of an entity type, where each subclass shares common attributes (inherited from the entity type) but also has additional attributes that are unique to the subclass.
How does ‘generalization’ in the EER model differ from ‘specialization’?
Generalization is the reverse of specialization. It’s the process of abstracting common properties of multiple entity types into a higher-level, generalized entity type. While specialization divides a single entity into multiple entities based on differences, generalization combines multiple entities based on similarities.
In EER modeling, what is a ‘subclass’?
A subclass is a more specific and refined version of an entity type. It inherits attributes from its superclass and may also have additional attributes that are not present in the superclass.
What does ‘aggregation’ refer to in EER?
Aggregation is a modeling technique in EER where a relationship between entities is treated as a higher-level entity. It allows relationships to participate in other relationships.
Can an entity be a part of more than one subclass in the EER model?
Yes, an entity can be a part of more than one subclass if the subclasses are overlapping. This means that an entity instance can belong to multiple subclasses within the same superclass.
Why might you use an EER diagram instead of a simple ER diagram?
EER diagrams offer more advanced modeling concepts and are beneficial when the real-world scenario to be modeled has complexities that cannot be efficiently captured using simple ER diagrams. Concepts like generalization, specialization, and aggregation in EER make it more expressive and versatile.
What is the primary distinction between ER and EER models?
The EER model extends the ER model by introducing advanced concepts like specialization/generalization, category (union type), and aggregation to represent more complex scenarios.
What does ‘total specialization’ mean in EER?
Total specialization means that every instance of the superclass must belong to some subclass.
What’s the difference between ‘partial specialization’ and ‘total specialization’?
In total specialization, every instance in the superclass must be a member of some subclass, whereas in partial specialization, an instance can exist in the superclass without belonging to any of its subclasses.
What is a ‘composite attribute’?
A composite attribute is an attribute that can be subdivided into other meaningful attributes, indicating a hierarchy of attributes
How is a ‘derived attribute’ represented in an EER diagram?
A derived attribute is typically represented by a dashed ellipse connected to its respective entity or relationship.
What is a ‘weak entity’ in EER modeling?
Answer: A weak entity is an entity that cannot be uniquely identified by its attributes alone and relies on a related entity (the owner entity) for its identification.
How is ‘category’ or ‘union type’ represented in EER?
Answer: A category or union type is used to represent entities that can be members of one or more disjoint sets. It is typically depicted using a circle in EER diagrams.
