ERD Symbols and Meanings

Entity Relationship Diagram (ERD) is a popular software engineering tool for database modeling and illustration the logical structure of databases, which uses one of two notations - Chen's or Crow’s Foot. Crow's foot notation is effective when used in software engineering, information engineering, structured systems analysis and design. Each of these notations applies its own set of ERD symbols. Crow's foot diagrams use boxes to represent entities and lines between these boxes to show relationships. Varied shapes at the ends of lines depict the cardinality of a given relationship. Chen's ERD notation is more detailed way to represent entities and relationships. ConceptDraw DIAGRAM application enhanced with all-inclusive Entity-Relationship Diagram (ERD) solution allows design professional ER diagrams with Chen's or Crow’s Foot notation on your choice. It contains the full set of ready-to-use standardized ERD symbols and meanings helpful for quickly drawing, collection of predesigned ERD samples, examples and templates. ConceptDraw Pro is a great alternative to Visio for Mac users as it offers more features and can easily handle the most demanding professional needs.

How to Build an Entity Relationship Diagram (ERD)

Entity Relationship Diagram Symbols

The semantic modeling method nowadays is successfully applied in database structure design. It is effective method of modeling the data structures, which is based on the meaning of these data. As a tool of semantic modeling, there are used different types of Entity-Relationship Diagrams. Entity Relationship Diagram (ERD) is applied to visually and clearly represent a structure of a business database. The main components of ERDs are: entity, relation and attributes. An entity is a class of similar objects in the model, each entity is depicted in the form of rectangle and has the name expressed by a noun. Relation is shown in the form of non-directional line that connects two entities. There are several notation styles used for ERDs: information engineering style, Chen style, Bachman style, Martin Style. The Entity Relationship Diagram symbols used for professional ERD drawing are predesigned by professionals and collected in the libraries of the Entity-Relationship Diagram (ERD) solution for ConceptDraw DIAGRAM software.

EXPRESS-G attribute symbols

This sample shows EXPRESS-G notation attribute symbols.
This example was drawn on the base of the Wikimedia Commons file: A 02B Attribute symbols.svg. [commons.wikimedia.org/ wiki/ File:A_ 02B_ Attribute_ symbols.svg]
This file is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication. [creativecommons.org/ publicdomain/ zero/ 1.0/ deed.en]
"Entity attributes allow to add "properties" to entities and to relate one entity with another one in a specific role. The name of the attribute specifies the role. Most datatypes can directly serve as type of an attribute. This includes aggregation as well.
There are three different kinds of attributes, explicit, derived and inverse attributes. And all these can be re-declared in a subtype. In addition an explicit attribute can be re-declared as derived in a subtype. No other change of the kind of attributes is possible.
* Explicit attributes are those with direct values visible in a STEP-File.
* Derived attributes get their values from an expression. In most cases the expression refers to other attributes of THIS instance. The expression may also use EXPRESS functions.
* Inverse attributes do not add "information" to an entity, but only name and constrain an explicit attribute to an entity from the other end." [EXPRESS (data modeling language). Wikipedia]
The EXPRESS-G notation example "EXPRESS-G attribute symbols" was designed using ConceptDraw PRO software extended with EXPRESS-G solution from the Software Development area of ConceptDraw Solution Park.

Data modeling

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EXPRESS-G data Modeling Diagram

Design elements - ER diagram (Chen notation)

"Chen's notation for entity–relationship modeling uses rectangles to represent entity sets, and diamonds to represent relationships appropriate for first-class objects: they can have attributes and relationships of their own. If an entity set participates in a relationship set, they are connected with a line.
Attributes are drawn as ovals and are connected with a line to exactly one entity or relationship set.
Cardinality constraints are expressed as follows:
- a double line indicates a participation constraint, totality or surjectivity: all entities in the entity set must participate in at least one relationship in the relationship set;
- an arrow from entity set to relationship set indicates a key constraint, i.e. injectivity: each entity of the entity set can participate in at most one relationship in the relationship set;
- a thick line indicates both, i.e. bijectivity: each entity in the entity set is involved in exactly one relationship.
- an underlined name of an attribute indicates that it is a key: two different entities or relationships with this attribute always have different values for this attribute.
Attributes are often omitted as they can clutter up a diagram; other diagram techniques often list entity attributes within the rectangles drawn for entity sets." [Entity–relationship model. Wikipedia]
The vector stencils library ERD, Chen's notation contains 13 symbols for drawing entity-relatinship diagrams using the ConceptDraw PRO diagramming and vector drawing software.
The example "Design elements - ER diagram (Chen notation)" is included in the Entity-Relationship Diagram (ERD) solution from the Software Development area of ConceptDraw Solution Park.

Chen's ERD

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Chen Notation

ERD, Chen's notation - Vector stencils library

The vector stencils library "ERD, Chen's notation" contains 13 ERD elements.
Use it for drawing ER-diagrams using Chen's notation in the ConceptDraw PRO diagramming and vector drawing software extended with the Entity-Relationship Diagram (ERD) solution from the Software Development area of ConceptDraw Solution Park.

Entity

Weak entity

Relationship

Identifying Relationship

Associative Entity

Participation

Optional participation

Recursive Relationship

Attribute

Key attribute

Weak key attribute

Derived attribute

Multivalue attribute

Used Solutions

Software Development >

Entity-Relationship Diagram (ERD)

ERD, Chen's notation - Vector stencils library

Entity

Weak entity

Relationship

Identifying Relationship

Associative Entity

Participation

Optional participation

Recursive Relationship

Attribute

Key attribute

Weak key attribute

Derived attribute

Multivalue attribute

Used Solutions

Software Development >

Entity-Relationship Diagram (ERD)

ERD, Chen's notation - Vector stencils library

Entity

Weak entity

Relationship

Identifying Relationship

Associative Entity

Participation

Optional participation

Recursive Relationship

Attribute

Key attribute

Weak key attribute

Derived attribute

Multivalue attribute

Used Solutions

Software Development >

Entity-Relationship Diagram (ERD)

ERD, Chen's notation - Vector stencils library

Entity

Weak entity

Relationship

Identifying Relationship

Associative Entity

Participation

Optional participation

Recursive Relationship

Attribute

Key attribute

Weak key attribute

Derived attribute

Multivalue attribute

Used Solutions

Software Development >

Entity-Relationship Diagram (ERD)

ERD, Chen's notation - Vector stencils library

Entity

Weak entity

Relationship

Identifying Relationship

Associative Entity

Participation

Optional participation

Recursive Relationship

Attribute

Key attribute

Weak key attribute

Derived attribute

Multivalue attribute

Used Solutions

Software Development >

Entity-Relationship Diagram (ERD)

ConceptDraw DIAGRAM ER Diagram Tool

Entity-relationship model, also called ER-model, is the main tool of domain modeling on the stage of conceptual design. The modeling of domain data structures is based on the use of graphical tools - Entity-Relationship diagrams (ER-diagrams). The core concepts of ER-Diagram are entity, attribute and relationship. ER-diagram lets visually represent the entities, helps effectively document all properties of designed system and to detail the data storages. To represent the elements at ER-model are commonly used Chen’s notation and Crow’s foot notation, each has its pros and cons. The entity on ER-diagram is represented in the form of rectangle, which specifies its name. An attribute is a property of the entity and relationship is an interaction between the entities. The relationship between two entities is called binary, between more than two entities - ternary. Specific software, such as ConceptDraw DIAGRAM with Entity-Relationship Diagram (ERD) solution from ConceptDraw Solution Park is helpful for easy creation Entity-Relationship Diagrams.

Notation & Symbols for ERD

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.

AWS Database - Vector stencils library

The vector stencils library "AWS Database" contains 30 Amazon Web Services database icons: Amazon DynamoDB symbols, Amazon Relational Database Service symbols, Amazon ElasticCache symbols, Amazon SimpleDB symbols, Amazon Redshift symbols.
Use it to draw AWS architecture diagrams of your cloud service.
The symbols example "AWS Database - Vector stencils library" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the AWS Architecture Diagrams solution from the Computer and Networks area of ConceptDraw Solution Park.

DynamoDB

Table

Item

Items

Attribute

Attributes

Global secondary index

Amazon RDS

RDS DB instance

RDS DB instance standby (Multi-AZ)

RDS DB instance read replica

MySQL DB instance

Oracle DB instance

MS SQL instance

PostgreSQL instance

SQL master

SQL slave

PIOP

ElastiCache

Cache node

Redis

Memcached

Amazon SimpleDB

Domain

Amazon Redshift

Solid state disks

DW2 Dense Compute

DW1 Dense Compute

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Computer and Networks >

AWS Architecture Diagrams

Employee ORM diagram

This object-role modeling (ORM) diagram sample shows model of employee data: birthdate, hiredate, rank, company car number. It was designed on the base of the Wikimedia Commons file: ORM-diagram-tkz-orm.png. [commons.wikimedia.org/ wiki/ File:ORM-diagram-tkz-orm.png]
"Facts.
Object-role models are based on elementary facts, and expressed in diagrams that can be verbalised into natural language. ...
This "fact-based" approach facilitates modeling, transforming, and querying information from any domain. ...
Attribute-free.
ORM is attribute-free: unlike models in the entity–relationship (ER) and Unified Modeling Language (UML) methods, ORM treats all elementary facts as relationships and so treats decisions for grouping facts into structures (e.g. attribute-based entity types, classes, relation schemes, XML schemas) as implementation concerns irrelevant to semantics. By avoiding attributes in the base model, ORM improves semantic stability and enables verbalization into natural language. ...
Fact-based modeling.
Fact-based modeling includes procedures for mapping facts to attribute-based structures, such as those of ER or UML. ...
Fact-based graphical notations are more expressive than those of ER and UML. ...
Design procedure.
System development typically involves several stages such as: feasibility study; requirements analysis; conceptual design of data and operations; logical design; external design; prototyping; internal design and implementation; testing and validation; and maintenance." [Object-role modeling. Wikipedia]
The object-role modeling diagram example "Employee ORM diagram" was designed using ConceptDraw PRO software extended with ORM Diagrams solution from Software Development area of ConceptDraw PRO Solution Park.

Object-role model

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Software Development >

Object-Role Modeling (ORM) Diagrams

Chen's ERD of MMORPG

"In software engineering, an entity–relationship model (ER model) is a data model for describing a database in an abstract way.Chen's notation for entity–relationship modeling uses rectangles to represent entity sets, and diamonds to represent relationships appropriate for first-class objects: they can have attributes and relationships of their own. If an entity set participates in a relationship set, they are connected with a line.
Attributes are drawn as ovals and are connected with a line to exactly one entity or relationship set." [Entity–relationship model. Wikipedia]
This sample Chen's ER-diagram illustrates the structure of a typical MMORP game.
"Massively multiplayer online role-playing game (MMORPG) mixes the genres of role-playing video games and Massively multiplayer online games, possibly in the form of web browser-based games, in which a very large number of players interact with one another within a virtual world.
As in all RPGs, players assume the role of a character (often in a fantasy world or science-fiction world) and take control over many of that character's actions. MMORPGs are distinguished from single-player or small multi-player online RPGs by the number of players, and by the game's persistent world (usually hosted by the game's publisher), which continues to exist and evolve while the player is offline and away from the game." [Massively multiplayer online role-playing game. Wikipedia]
This ERD example was redrawn using the ConceptDraw PRO diagramming and vector drawing software from the Wikipedia file: ER Diagram MMORPG.png. [en.wikipedia.org/ wiki/ File:ER_ Diagram_ MMORPG.png]
This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. [creativecommons.org/ licenses/ by-sa/ 3.0/ deed.en]
This Chen's ERD example is included in the Entity-Relationship Diagram (ERD) solution from the Software Development area of ConceptDraw Solution Park.

Chen's ERD

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Chen Notation

Design Element: Chen for Entity Relationship Diagram - ERD

Design Element: Chen <br>for Entity Relationship Diagram - ERD *

Entity-Relationship Diagrams (ERDs) were developed and introduced as a convenient and visual tool for the data modeling, they are the perfect way for easy determining data and also relationships between them. The first standard notation for ERD was proposed by Chen. Chen's notation is very rich on the data modeling tools and standard notation symbols and elements for drawing easy understandable Entity-relationship diagrams, Attribute diagrams, Decomposition charts, which are especially popular for designing relational databases. The entity is the main term, it is a set of instances abstract or real objects with common characteristics or attributes. Any system's object is represented by one uniquely identified entity, relationships describe the links between the entities. ConceptDraw DIAGRAM diagramming software, which includes the Entity-Relationship Diagram (ERD) solution, offers all needed tools for professional drawing ER diagrams. Specially developed vector ERD design elements according to Chen and Crow's Foot notations are indispensible for professional ERDs design.

Anyone Have an ERD Symbols Quick Reference?

ERD drawing becomes easier with predesigned entity relationship symbols, work flow shapes, entity relationship stencils. All variety of ERD symbols you may need for ERDs design is packed into libraries and templates from Entity-Relationship Diagram (ERD) Solution for ConceptDraw DIAGRAM diagramming and vector drawing software. But anyone have an ERD symbols quick reference? Detailed reference information for them is represented at the tables.

Design elements - Bank UML object diagram

The vector stencils library "Bank UML object diagram" contains 11 shapes for drawing UML object diagrams.
Use it for object-oriented modeling of your bank information system.
"In the Unified Modeling Language (UML), an object diagram focuses on some particular set of objects and attributes, and the links between these instances. A correlated set of object diagrams provides insight into how an arbitrary view of a system is expected to evolve over time. ...
Each object and link on an object diagram is represented by an InstanceSpecification. This can show an object's classifier (e.g. an abstract or concrete class) and instance name, as well as attributes and other structural features using slots. Each slot corresponds to a single attribute or feature, and may include a value for that entity. ...
The name on an instance specification optionally shows an instance name, a ':' separator, and optionally one or more classifier names separated by commas. The contents of slots, if any, are included below the names, in a separate attribute compartment. A link is shown as a solid line, and represents an instance of an association. ...
An object instance may be called an instance specification or just an instance. A link between instances is generally referred to as a link. Other UML entities, such as an aggregation or composition symbol (a diamond) may also appear on an object diagram." [Object diagram. Wikipedia]
This example of UML object diagram symbols for the ConceptDraw PRO diagramming and vector drawing software is included in the ATM UML Diagrams solution from the Software Development area of ConceptDraw Solution Park.

UML object diagram symbols

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ATM UML Diagrams

ConceptDraw DIAGRAM : Able to Leap Tall Buildings in a Single Bound

ConceptDraw DIAGRAM is the world’s premier cross-platform business-diagramming tool. Many, who are looking for an alternative to Visio, are pleasantly surprised with how well they can integrate ConceptDraw DIAGRAM into their existing processes. With tens of thousands of template objects, and an easy method for importing vital custom objects from existing Visio documents, ConceptDraw DIAGRAM is a powerful tool for making extremely detailed diagrams, quickly and easily.