ERD Entity Relationship Diagrams Exam
Questions and Answers
Purpose of an ERD - ANSWERS -- The database analyst/designer gains a better understanding of
the information to be contained in the database through the process of constructing the ERD.
- The ERD serves as a documentation tool.
- Finally, the ERD is used to communicate the logical structure of the database to users. In
particular, the ERD effectively communicates the logic of the database to users.
Components of an ERD - ANSWERS -1. Entity
2. Relationship
3. Cardinality
4. Attribute
Entity in an ERD - ANSWERS -Any object or event about which someone chooses to collect data
- May be a person, place, or thing (ex. salesperson, city, product)
- May be an event or unit of time (ex. a sale, a month/year)
Entity Relationship Diagram (ERD) - ANSWERS -- allows us to sketch database designs
- a graphical tool for modeling data.
- widely used in database design
- a graphical representation of the logical structure of a database
- a model that identifies the concepts or entities that exist in a system and the relationships
between those entities
** the "blueprint" from which the actual data is stored — the output of the design phase.
, Different types of relationships - ANSWERS -1. One-to-one (direct relationship)
- Exists when one of the second entity occurs for the first entity
2. One-to-many
- Exists when one occurrence of the first entity can relate to many instances of the second entity
3. Many-to-many
- Exists when one instance of the first entity can relate to many instances of the second entity
and one instance of the second entity can relate to many instances of the first entity.
** Associations between entities
** Self-join relationship—an entity with a relationship connecting to itself.
Classifications of Relationships - ANSWERS -1. Optional Relationship
- An Employee may or may not be assigned to a Department
- A Patient may or may not be assigned to a Bed
2. Mandatory Relationship
- Every Course must be taught by at least one Teacher
- Every mother have at least a Child
Cardinality - ANSWERS -A way to express the number of entities to which another entity can be
associated via a relationship set.
______ Constraints - the number of instances of one entity that can or must be associated with
each instance of another entity.
Questions and Answers
Purpose of an ERD - ANSWERS -- The database analyst/designer gains a better understanding of
the information to be contained in the database through the process of constructing the ERD.
- The ERD serves as a documentation tool.
- Finally, the ERD is used to communicate the logical structure of the database to users. In
particular, the ERD effectively communicates the logic of the database to users.
Components of an ERD - ANSWERS -1. Entity
2. Relationship
3. Cardinality
4. Attribute
Entity in an ERD - ANSWERS -Any object or event about which someone chooses to collect data
- May be a person, place, or thing (ex. salesperson, city, product)
- May be an event or unit of time (ex. a sale, a month/year)
Entity Relationship Diagram (ERD) - ANSWERS -- allows us to sketch database designs
- a graphical tool for modeling data.
- widely used in database design
- a graphical representation of the logical structure of a database
- a model that identifies the concepts or entities that exist in a system and the relationships
between those entities
** the "blueprint" from which the actual data is stored — the output of the design phase.
, Different types of relationships - ANSWERS -1. One-to-one (direct relationship)
- Exists when one of the second entity occurs for the first entity
2. One-to-many
- Exists when one occurrence of the first entity can relate to many instances of the second entity
3. Many-to-many
- Exists when one instance of the first entity can relate to many instances of the second entity
and one instance of the second entity can relate to many instances of the first entity.
** Associations between entities
** Self-join relationship—an entity with a relationship connecting to itself.
Classifications of Relationships - ANSWERS -1. Optional Relationship
- An Employee may or may not be assigned to a Department
- A Patient may or may not be assigned to a Bed
2. Mandatory Relationship
- Every Course must be taught by at least one Teacher
- Every mother have at least a Child
Cardinality - ANSWERS -A way to express the number of entities to which another entity can be
associated via a relationship set.
______ Constraints - the number of instances of one entity that can or must be associated with
each instance of another entity.
