Entity Relationship Modeling Flashcards
What does connectivity describe in entity relationship modeling?
Connectivity describes the relationship classification.
What does cardinality express in entity relationship modeling?
Cardinality expresses minimum and maximum number of entity occurrences associated with one occurrence of related entity.
What is a relationship instance?
A relationship instance is an association between entity instances, where each instance associates exactly one entity instance from each participating entity type.
What is an identifier in entity relationship modeling?
An identifier (primary key) is one or more attributes that uniquely identify each entity instance.
What is a candidate key?
A candidate key is a simple or composite key that is unique and minimal.
What is a composite key?
A composite key is a primary key composed of more than one attribute.
What is an alternate key?
An alternate key is any candidate key that is not chosen as the primary key.
What is a foreign key?
A foreign key is an attribute in a table that references the primary key in another table or can be null.
True or False: Both foreign and primary keys must be of the same data type.
True.
What should be done if multivalued attributes exist?
The designer must create a new entity composed of the original multivalued attribute’s components.
What is existence dependence in entity relationships?
Existence dependence means an entity exists in the database only when it is associated with another related entity occurrence.
Entity is existence-dependent if it has a mandatory foreign key—that is, a foreign key attribute that cannot be null.
What is existence independence in entity relationships?
Existence independence means an entity can exist apart from one or more related entities.
What characterizes a weak entity?
A weak entity is existence-dependent and has a primary key that is partially or totally derived from the parent entity.
What is a strong entity?
A strong entity is one that exists independently of other entity types.
What is an identifying relationship?
An identifying relationship is the relationship between a weak entity type and its owner.
Weak entity inherits part of its primary key from its strong counterpart
What are the types of relationship participation?
- Optional participation
- Mandatory participation
What is a unary relationship?
A unary relationship is an association maintained within a single entity.
What is a binary relationship?
A binary relationship is an association between two entities.
What is a ternary relationship?
A ternary relationship is an association among three entities.
What is the role of associative (composite) entities?
Associative entities are used to implement M:N relationships and are composed of primary keys of each of the entities to be connected.
May also contain additional attributes that play no role in connective process
Fill in the blank: A weak entity meets two conditions: it is ______ and its primary key is partially or totally derived from a parent entity.
existence-dependent.
What is a derived attribute?
A derived attribute is a value that may be calculated from other attributes and need not be physically stored within the database.
What notation does Chen use to represent attributes in ER modeling?
Chen notation uses ovals connected to entity rectangles.
What notation does Crow’s Foot use to represent attributes in ER modeling?
Crow’s Foot notation writes attributes in an attribute box below the entity rectangle.
