Notation & Symbols for ERD

Creation of the entity-relationship model is one of the most important stages in the process of creating databases and modeling of business processes. Entity Relationship Diagram (ERD) reflects reality and allows you to get the most complete picture about the actual data requirements that are set at the company.

The entity-relationship model described in form of ERD represents the information that is gathered and used at the conduct of business. It visually shows how the database or application system will look, but doesn't disclose a way of realization. The ERD doesn't depend on the choice of database producer. It groups the data into separate entities and links these entities to each other on the base of business rules. The entity has the contents and represents some object about which is needed to store information. The business rules is a line of conduct and procedures for the business organization, they describe how the company is functioning.

The ER diagram is constructed from the specific ERD graphic elements. There are used 2 types of ERD notations: Chen and Crow's Foot.

A complete set of work flow shapes, notation & symbols for ERD, entity relationship stencils, included in Entity-Relationship Diagram (ERD) solution for ConceptDraw DIAGRAM software, makes drawing diagrams based on ERD notation as smooth as possible.

Example 1. Entity relationship diagram (ERD) symbols, Crow's Foot notation

All these ERD symbols are vector, you can drag to the document to construct the ER Diagram, resize any of them without loss of quality, change their color to make your diagram more attractive and colorful.

ERD Chen's notation

Symbol	Shape Name	Symbol Description
Entities
	Entity	An entity is represented by a rectangle which contains the entity’s name.
	Weak Entity	An entity that cannot be uniquely identified by its attributes alone. The existence of a weak entity is dependent upon another entity called the owner entity. The weak entity’s identifier is a combination of the identifier of the owner entity and the partial key of the weak entity.
	Associative Entity	An entity used in a many-to-many relationship (represents an extra table). All relationships for the associative entity should be many
Attributes
	Attribute	In the Chen notation, each attribute is represented by an oval containing atributte’s name
	Key attribute	An attribute that uniquely identifies a particular entity. The name of a key attribute is underscored.
	Multivalued attribute	An attribute that can have many values (there are many distinct values entered for it in the same column of the table). Multivalued attribute is depicted by a dual oval.
	Derived attribute	An attribute whose value is calculated (derived) from other attributes. The derived attribute may or may not be physically stored in the database. In the Chen notation, this attribute is represented by dashed oval.
Relationships
	Strong relationship	A relationship where entity is existence-independent of other entities, and PK of Child doesn’t contain PK component of Parent Entity. A strong relationship is represented by a single rhombus
	Weak (identifying) relationship	A relationship where Child entity is existence-dependent on parent, and PK of Child Entity contains PK component of Parent Entity. This relationship is represented by a double rhombus.

Example 2. ER Diagram - Chen's Notation

ERD Crow’s Foot notation

Symbol	Meaning
Relationships (Cardinality and Modality)
	Zero or More
	One or More
	One and only One
	Zero or One
Many - to - One
	a one through many notation on one side of a relationship and a one and only one on the other
	a zero through many notation on one side of a relationship and a one and only one on the other
	a one through many notation on one side of a relationship and a zero or one notation on the other
	a zero through many notation on one side of a relationship and a zero or one notation on the other
Many - to - Many
	a zero through many on both sides of a relationship
	a one through many on both sides of a relationship
	a zero through many on one side and a one through many on the other
	a one and only one notation on one side of a relationship and a zero or one on the other
	a one and only one notation on both sides

Example 3. ER Diagram - Crow's Foot Notation

The samples you see on this page were created in ConceptDraw DIAGRAM using the Entity-Relationship Diagram (ERD) solution from Software Development area of ConceptDraw Solution Park. An experienced user spent 10 minutes creating these samples.

Use the Entity-Relationship Diagram (ERD) Solution for ConceptDraw DIAGRAM software to create quick and easy your own professional looking ERDs using Crow's Foot and Chen notations.

All source documents are vector graphic documents. They are available for reviewing, modifying, or converting to a variety of formats (PDF file, MS PowerPoint, MS Visio, and many other graphic formats) from the ConceptDraw STORE. The Entity-Relationship Diagram (ERD) Solution is available for all ConceptDraw DIAGRAM or later users.

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