CIN623 Database Design and Programming
ER Diagram Assignment 1 due: 04/10/2013
1. In the context of entity modeling, explain the following terms:

a. Entity type- an entity-type is a category whereas an entity, strictly speaking, is an instance of a given entity-type.

b. Attribute- an attribute may describe a component of the database, such as a table or a field, or may be used itself as another term for a field.

c. Entity model- The Entity Data Model (EDM) is a set of concepts that describe the structure of data, regardless of its stored form.

d. Degree- The degree of a relation is the number of attributes the relation has in it i.e. how many instances of an entity can exist at one end of the relationship for each entity instance at the other end.

e. Optionality- The minimum number of an entity instance that are possible at one end of the relationship for each entity instance at the other end. For example, a dash line indicates an optional relationship end that is read as "maybe". A solid line indicates a mandatory relationship end that is read as "must be".

f. unary relationship- Association is maintained within single entity.

g. Entity- Used in Logical Data Modeling, an Entity is a thing of significance, either real or conceptual, about which the business or system being modeled needs to hold information. For example, if the business needs to process sales orders, an Entity to represent sales orders would be recorded. An Entity generally corresponds to a physical table.

h. Relationship- A named, significant association between two entities. Each end of the relationship shows the degree of how the entities are related and the optionality. i. entity relationship diagram- ERD represents conceptual database as viewed by end user
ERDs depict database’s main components:
Entities
Attributes
Relationships

j. Cardinality- Expresses