Chen ER Diagram - Entity-Relationship Diagram in Chen Notation
Chen Diagram Symbols
Chen ER diagram offers these symbols:
An entity represents a set of objects with the same attributes within a data model. It is depicted as a rectangle.
A week entity is a type of entity that does not have any unique key for the attribute tuples. A weak entity depends on another entity, that is considered its owner. It is depicted as a rectangle with a double border.
An associative entity represents a many-to-many relationship that is expressed by another entity (or a table in database). It is depicted as a rectangle with a diamond inside.
An attribute contains a piece of information that describes an entity. An attribute is depicted as an ellipse. There are these types of attributes:
A key attribute represents an identifying attribute. The key attributes define a combination of keys that unambiguously define a tuple within an entity.
Weak Key Attribute
A weak key attribute (or partial key) is a attribute that in combination with owner's key creates a key for weak entity.
Multi Value Attribute
A multi value attribute can have multiple distinctive values. The attribute is represented by an array of values.
A derived attribute represents an attribute that does not physically exist in permanently stored form. It is an attribute that is calculated from other attributes.
A relationship defines the interconnection between two entities. It is depicted as a diamond. There are two specific types of relationships:
- Strong relationship - is depicted as a diamond with a normal line border.
- Weak relationship (Identifying) - is depicted as a diamond with a double line border.
When entity A connected with a strong relationship to entity B, the existence of entity A is independent of the existence of entity B.
When entity A connected with a weak relationship to entity B, the existence of entity A depends on B entity existence.
The Chen ER diagram allows you to define a type of entity participating in a relationship, it can be:
- Total participation - is depicted as a double line
- Partial participation - is depicted as a solid line
- Optional participation - is depicted as a dashed line
The relationship can connect one or multiple tuples from one entity to one or multiple tuples of another entity. You can use these cardinalities for the relationships:
- One-to-one (1:1)
- One-to-many (1:N)
- Many-to-one (N:1)
- Many-to-many (M:N)
Chen ER Diagram Tool
Chen ER diagrams can be created and edited with the ER diagram tool Software Ideas Modeler.