17) Entities have attributes that describe characteristics of the entity.
18) An identifier is an attribute whose value is associated with every entity in the data model.
19) Entities have relationships to attributes but not to each other.
20) In an entity-relationship (E-R) diagram, a line is used to represent a relationship between two entities.
21) The notation N:N is used to indicate a many-to-many relationship in an E-R diagram.
22) While representing the relationship between two entities in an entity-relationship diagram, the N:N notation is used to indicate that the same number of entities are present on each end of the relationship.
23) 1:N means that more than one entity is allowed on each side of the relationship.
24) The crow's foot notation shows the minimum number of entities that can be involved in a relationship.
25) The maximum number of entities that can be involved in a relationship is known as maximum cardinality.
26) In an entity-relationship diagram, a vertical bar on a line indicates that at least one entity of that type is required in the relationship.