Software Design Center

Entity
An entity is an object or concept about which you want to store information.
Learn how to edit text on an entity.

Weak Entity
Attributes are the properties or characteristics of an entity.
Learn how to edit text on this object.

Key attribute
A key attribute is the unique, distinguishing characteristic of the entity. For example, an employee's social security number might be the employee's key attribute.

Multivalued attribute
A multivalued attribute can have more than one value. For example, an employee entity can have multiple skill values.

Derived attribute
A derived attribute is based on another attribute. For example, an employee's monthly salary is based on the employee's annual salary.

Relationships
Relationships illustrate how two entities share information in the database structure.

Learn how to draw relationships:
First, connect the two entities, then drop the relationship notation on the line.

Cardinality
Cardinality specifies how many instances of an entity relate to one instance of another entity.

Ordinality is also closely linked to cardinality. While cardinality specifies the occurences of a relationship, ordinality describes the relationship as either mandatory or optional. In other words, cardinality specifies the maximum number of relationships and ordinality specifies the absolute minimum number of relationships.

To learn how to express cardinality in SmartDraw, click here.

Recursive relationship
In some cases, entities can be self-linked. For example, employees can supervise other employees.