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 PRO software, makes drawing diagrams based on ERD notation as smooth as possible.

Notation & Symbols for ERD

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
ERD Symbols and Meaning - Entity Entity An entity is represented by a rectangle which contains the entity’s name.
ERD Symbols and Meaning - Weak Entity 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.
ERD Symbols and Meaning - Associative 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
ERD Symbols and Meaning - Attribute Attribute In the Chen notation, each attribute is represented by an oval containing atributte’s name
ERD Symbols and Meaning - Key attribute Key attribute An attribute that uniquely identifies a particular entity. The name of a key attribute is underscored.
ERD Symbols and Meaning - Multivalue attribute 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.
ERD Symbols and Meaning - Derived attribute 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
ERD Symbols and Meaning - Relationship 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
ERD Symbols and Meaning - Identifying Relationship 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.

ER Diagram - Chen's Notation

Example 2. ER Diagram - Chen's Notation


ERD Crow’s Foot notation

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

ER Diagram - Crow's Foot Notation

Example 3. ER Diagram - Crow's Foot Notation

The samples you see on this page were created in ConceptDraw PRO 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 PRO 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 PRO v9.5 or later users.






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