A required attribute: is an attribute that must have a value.
An optional attribute: is an attribute that does not require a value.
Composite attribute: is an attribute that can be subdivided to yield additional attributes.
Simple attribute: is an attribute that cannot be subdivided.
Single-valued-attribute: is an attribute that can only have single value.
multivalued attribute : an attribute can have many values.
A derived attribute: is an attribute whose value is calculated from other attributes.
The entities that participate in a relationship are also known as participants.
Cardinality: expresses the minimum and maximum number of entity occurrences associated with one occurrence of related entity.
An entity is said to be existence-dependant if it can exist in the database when it is associated with another related entity occurrence.
If an entity can exist a part from one or more related entities it is said to be existence-independent.
A weak relationship (non-identifying-relationship): exists if the PK of related entity does not contain a PK component of parent entity.
A strong relationship (identifying-relationship): exists if the PK of related entity contains a PK component of parent entity.
Optional participation: means that one entity occurrence does not require a corresponding entity occurrence in a particular relationship.
Mandatory participation: means that one entity occurrence requires a corresponding entity occurrence in a particular relationship.
Written by : Mohammed Alaslani
