22 Questions
What is the purpose of conceptual data modeling?
To document information requirements and define data integrity rules
What is the main characteristic of an associative entity in ER modeling?
It is an entity type that associates instances of one or more entity types
What is the primary focus of business rules in ER modeling?
Ensuring data integrity
What is the purpose of an associative entity in ER modeling?
To associate instances of one or more entity types
What is the role of data modeling in ensuring data integrity?
To ensure consistency and accuracy of data
What is the outcome of the data modeling process?
A conceptual data model
What is an identifier in ER modeling?
A candidate key that has been selected as the unique, identifying characteristic for an entity type
What is a multivalued attribute in ER modeling?
An attribute that may take on more than one value for each entity instance
What is a repeating group in ER modeling?
A set of two or more multivalued attributes that are logically related
What is the degree of a unary relationship in ER modeling?
One
What is a binary relationship in ER modeling?
A relationship between the instances of two entity types
What is an ER model primarily used to represent?
Detailed, logical representation of entities, associations, and data elements
What is an important rule for selecting an identifier in ER modeling?
The candidate key will not change its value over the life of each instance
What is an entity instance in ER modeling?
A single occurrence of an entity type
In ER modeling, what is an attribute?
A named property or characteristic of an entity
What is a characteristic of an identifier in ER modeling?
It is guaranteed to have valid values and not null
What is the purpose of relationships in ER modeling?
To establish associations between entity instances
What is used to express an ER model?
Entity Relationship Diagram (ERD) or Enhanced Entity Relationship Diagram (EERD)
What is an entity in ER modeling?
A person, place, object, event or concept in the user environment about which data is to be maintained
What is an entity type in ER modeling?
A collection of entities that share common properties or characteristics
What is the purpose of ER modeling?
To represent business rules and data integrity constraints
What are the three main constructs used in ER modeling?
Data entities, relationships and their associated attributes
Study Notes
Associative Entities
- An associative entity is an entity type that associates instances of one or more entity types and contains attributes peculiar to the relationship between those entity instances.
- The data modeler chooses to model the relationship as an entity type.
Attributes
- Multivalued attribute: an attribute that may take on more than one value for each entity instance.
- Repeating group: a set of two or more multivalued attributes that are logically related or repeat together.
Entity Relationship Modeling
- Entity Relationship data model (ER model) is a detailed, logical representation of the entities, associations, and data elements for an organization or business area.
- ER model uses three main constructs: data entities, relationships, and their associated attributes or properties.
- An ER model is normally expressed as an Entity Relationship Diagram (ERD) or Enhanced Entity Relationship Diagram (EERD).
Entities
- An entity is a concept in the user environment about which organization wishes to maintain data.
- An entity has its own identity, which distinguishes it from each other entity.
- Entity type: collection of entities that share common properties or characteristics.
- Entity instance: single occurrence of an entity type.
Identifiers
- Identifier: a candidate key that has been selected as the unique, identifying characteristic for an entity type.
- Selection rules for an identifier:
- The candidate key will not change its value over the life of each instance.
- For each instance, the attribute is guaranteed to have valid values (not null).
- Avoid using intelligent identifiers, whose structure indicates classification, locations, and so on.
Relationships
- Relationships are the glue that holds together the various components of an E-R model.
- A relationship is an association between instances of one or more entity types that is of interest to the organization.
- Degree: the number of entity types that participate in a relationship.
- Three most common relationships in E-R model:
- Unary relationship: a relationship between instances of one entity type. Also called a recursive relationship.
- Binary relationship: a relationship between instances of two entity types.
- Cardinality and time dimensions: are all instances of each object the same?
This quiz covers entity relationship modeling concepts, including restrictions on participation, history keeping, and transfer of participation between instances. It also touches on associative entities and bridge entities in database systems.
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