Entity Relationship Diagram Symbols

About Entity-relationship Diagram


The so-called semantic modeling method nowadays is commonly used in database structure design. Semantic modeling is modeling data structures, based on the meaning of these data. Different variants of the entity-relationship diagrams are used as a tool for the semantic modeling. ER-model based diagrams have three main components: an entity, a relation and attributes. An entity is a class of similar objects, information about which should be taken into account in the model. Each entity must have a name, expressed by a noun in the singular. Examples of entities can be such classes of objects as "Supplier", "Employee", "Invoice". Each entity in the model is depicted in the form of a rectangle with the name.

While determining the type of entity it is necessary to be sure that each instance of an entity may be indistinguishable from any other instance of the same entity.

Relation is presented in the form of non-directional line connecting two entities or leading from the entity to itself. In the place of "docking" an entity uses:

  • three-point entry to the entity rectangle, if many instances of the entity may be used for this relation
  • single-point entry, if relation can (or should) participate in only one instance of the entity.

Relation between entities "ticket" and "passenger" connects passengers and tickets. One side of the relation with a label "for" is a many-to-many relation which allows to relate more than one ticket to a passenger, and each ticket must be linked to any passenger. Another side of the relation with a label "have" is a zero or one relation, which shows that each ticket can belong to only one passenger, and the passenger is not obliged to have at least one ticket. Attribute of an entity is a detail or feature that is used for verification, identification, classification, numerical characteristics or expressing status of the entity. Attribute names are recorded in the rectangle representing an entity under entity name. For instance, an entity "human being" may have such attributes as gender, year of birth, first name, etc.


Entity Relationship Diagram

It is the specialized Entity Relationship diagram symbols, and the meanings of those symbols


Entity Relationship Diagram Symbols — Chen 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.

Entity Relationship Diagram Symbols — Crow’s Foot notation

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

There are many notation styles that express cardinality:

  • Information Engineering Style;
  • Chen Style;
  • Bachman Style;
  • Martin Style;

Entity Relationship Diagram Symbols

Example 1. Entity relationship diagram symbols, Chen's and Crow’s Foot notation

Entity-Relationship model making possibility to describe a database by abstract way. The data in database tables can be the point to data in other tables - for instance, your entry in the database could point to several entries.

Entity relationship diagram

Example 2. Entity Relationship Diagram (ERD) Software (Windows)

ConceptDraw PRO software thanks to the included Entity-Relationship Diagram (ERD) solution gives the ability to describe visually a database using the Chen's and Crow’s Foot notation icons for drawing ER diagrams (ERD).

Entity Relationship Diagram ERD Software

Example 3. Entity Relationship Diagram (ERD) Software (macOS)

The Entity-Relationship Diagram (ERD) solution from ConceptDraw Solution Park extends ConceptDraw PRO vector graphics and diagramming software with the ability to describe a database using the Entity-Relationship model. It provides entity relationship diagram examples, templates and library of vector stencils with ERD symbols.

Use ConceptDraw PRO enhanced with Entity-Relationship Diagram (ERD) solution to design you own entity relationship diagrams using Chen's or Crow's Foot notations.




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ERD Symbols and Meanings

A database is a data collection, structured into some conceptual model. Two most common approaches of developing data models are UML diagrams and ER-model diagrams. There are several notations of entity-relationship diagram symbols and their meaning is slightly different. Crow’s Foot notation is quite descriptive and easy to understand, meanwhile, the Chen notation is great for conceptual modeling. An entity relationship diagrams look very simple to a flowcharts. The main difference is the symbols provided by specific ERD notations. There are several models applied in entity-relationship diagrams: conceptual, logical and physical. Creating an entity relationship diagram requires using a specific notation. There are five main components of common ERD notations: Entities, Actions, Attributes, Cardinality and Connections. The two of notations most widely used for creating ERD are Chen notation and Crow foot notation. By the way, the Crow foot notation originates from the Chen notation - it is an adapted version of the Chen notation.Entity Relationship Diagram Symbols and Meaning - crow
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Entity Relationship Diagram Examples

An abstract representation is usually the first thing you will need while developing a database. To understand the ways that databases are structured, you should look through entity-relationship diagram examples and see the notations features and attributes. With an entity-relationship model you can describe a database of any complexity. This Entity-relationship diagram is a tool for software developers. It enables every element of database to be managed, communicated and tested before release. This ERD was created using symbols advocated by Chen's notation. Because of a linguistic origin of the Chen’s notation, the boxes representing entities could be interpreted as nouns, and the relationships between them are in verb form, shown on a diagram as a diamond.Entity Relationship Diagram Examples
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Process Flowchart

When trying to figure out the nature of the problems occurring within a project, there are many ways to develop such understanding. One of the most common ways to document processes for further improvement is to draw a process flowchart, which depicts the activities of the process arranged in sequential order — this is business process management. ConceptDraw PRO is business process mapping software with impressive range of productivity features for business process management and classic project management. This business process management software is helpful for many purposes from different payment processes, or manufacturing processes to chemical processes. Business process mapping flowcharts helps clarify the actual workflow of different people engaged in the same process. This samples were made with ConceptDraw PRO — business process mapping software for flowcharting and used as classic visio alternative because its briefly named "visio for mac" and for windows, this sort of software named the business process management tools. This flowchart diagram shows a process flow of project management. The diagram that is presented here depicts the project life cycle that is basic for the most of project management methods. Breaking a project into phases allows to track it in the proper manner. Through separation on phases, the total workflow of a project is divided into some foreseeable components, thus making it easier to follow the project status. A project life cycle commonly includes: initiation, definition, design, development and implementation phases. Distinguished method to show parallel and interdependent processes, as well as project life cycle relationships. A flowchart diagram is often used as visual guide to project. For instance, it used by marketing project management software for visualizing stages of marketing activities or as project management workflow tools. Created with ConceptDraw PRO — business process mapping software which is flowcharting visio alternative or shortly its visio for mac, this sort of software platform often named the business process management tools.business process flowcharts, flowchart symbols, process flow diagram, workflow diagram, flowchart maker
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ConceptDraw PRO - business process modeling software for mac offers the Business Process Diagram Solution with powerful tools to help you easy represent the business processes and create the business process diagrams based on BPMN 1.2 and BPMN 2.0 standards that allows to create of both simple and complex (nested) models of processes. There are 16 BPMN 1.2 and BPMN 2.0 stencil libraries containing 230 vector objects: Rapid Draw library, Connections library, Gateways and Artifacts libraries, Data library, Gateways library, Choreographies library, Conversations library, Activities libraries, Events libraries, Expanded Objects libraries, Swim lanes libraries.Choreography model diagram BPMN 2.0 - Purchasing process choreography diagram
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Data processing can be very complex sometimes. If you are interested in facilitating your work with data, it’s time to learn how to draw flowcharts with special software or using just a piece of paper. The list of flowchart basic symbols includes rectangles, diamond, ellipses etc. and is used to represent processes, actions, decisions or data processing. A well-done flowchart bring the clearness of the sequence of a process stages. There are number of symbols that can be used in flow charts to show various sorts of steps. The basic flowchart can be created using a few of them: Process, Decision, Start/Finish. A basic element of a flowchart represents a simple action and looks like a box, that contains a description of the action. The depicting of actions sequence is made with arrows between corresponding action boxes, as you can see on the sample diagram. Also it shows the symbols for flowchart start and finish steps. ConceptDraw Flowcharts solution provides the ability to build basic flow charts as well as the ones of any size and complexity with a minimum of actions.How to Draw a Flowchart
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Design Element: Crows Foot for Entity Relationship Diagram - ERD

The first thing that usually comes to mind when talking about database models is ER-diagrams, and the ways to create them. The second most recognizable notation is the Crow’s Foot, which visually differs from Chen’s notation. Actually, it doesn’t matter which notation you’ll use for your entity relationship diagram (ERD), but the content is what matters. When designing an Entity-Relationship Diagram one need to use a certain notated symbols that were developed and standardized especially for databases description. First of them - the Chen’s notation had a linguistic origin. It includes rectangle boxes to show entities that may be described as nouns, and the relationships between them described as verbs depicted in a form of diamond. Finally the Chen’s notation was simplified up to the Crow’s Foot notation. It represents a relationship as labeled line. It is precisely this notation is shown in the given figure. ConceptDraw PRO together with its Entity-Relationship Diagram (ERD) solution is designed to support professionals who deals with creating ER diagrams using the element of both - Chen’s and Crow's Foot notations.Entity Relationship Diagram, Design Elements - Crows Foot  (Win Mac)
Picture: Design Element: Crows Foot for Entity Relationship Diagram - ERD
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