Entity Relationship Diagram Symbols | Professional ERD Drawing (2022)

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 Symbols | Professional ERD Drawing (1)

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
Entity Relationship Diagram Symbols | Professional ERD Drawing (2) Entity An entity is represented by a rectangle which contains the entity’s name.
Entity Relationship Diagram Symbols | Professional ERD Drawing (3) 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.
Entity Relationship Diagram Symbols | Professional ERD Drawing (4) 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
Entity Relationship Diagram Symbols | Professional ERD Drawing (5) Attribute In the Chen notation, each attribute is represented by an oval containing atributte’s name
Entity Relationship Diagram Symbols | Professional ERD Drawing (6) Key attribute An attribute that uniquely identifies a particular entity. The name of a key attribute is underscored.
Entity Relationship Diagram Symbols | Professional ERD Drawing (7) 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.
Entity Relationship Diagram Symbols | Professional ERD Drawing (8) 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
Entity Relationship Diagram Symbols | Professional ERD Drawing (9) 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
Entity Relationship Diagram Symbols | Professional ERD Drawing (10) 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)
Entity Relationship Diagram Symbols | Professional ERD Drawing (11) Zero or One
Entity Relationship Diagram Symbols | Professional ERD Drawing (12) One or More
Entity Relationship Diagram Symbols | Professional ERD Drawing (13) One and only One
Entity Relationship Diagram Symbols | Professional ERD Drawing (14) Zero or More
Many - to - One
Entity Relationship Diagram Symbols | Professional ERD Drawing (15) a one through many notation on one side of a relationship and a one and only one on the other
Entity Relationship Diagram Symbols | Professional ERD Drawing (16) a zero through many notation on one side of a relationship and a one and only one on the other
Entity Relationship Diagram Symbols | Professional ERD Drawing (17) a one through many notation on one side of a relationship and a zero or one notation on the other
Entity Relationship Diagram Symbols | Professional ERD Drawing (18) a zero through many notation on one side of a relationship and a zero or one notation on the other
Many - to - Many
Entity Relationship Diagram Symbols | Professional ERD Drawing (19) a zero through many on both sides of a relationship
Entity Relationship Diagram Symbols | Professional ERD Drawing (20) a zero through many on one side and a one through many on the other
Entity Relationship Diagram Symbols | Professional ERD Drawing (21) a one through many on both sides of a relationship
Entity Relationship Diagram Symbols | Professional ERD Drawing (22) a one and only one notation on one side of a relationship and a zero or one on the other
Entity Relationship Diagram Symbols | Professional ERD Drawing (23) 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;

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.

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

ConceptDraw DIAGRAM 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).

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

(Video) Entity Relationship Diagram (ERD) Tutorial - Part 1

Very commonly used in the database structure design, the sematic modelling method is one the ways of describing data structures as well as its modelling, based on the meaning of this data. ER-model based diagrams (ERD) consist of these main components: relation, entity and attributes. To be able to create such diagram, you have to mention the entities with their names presented in a form of a rectangle and the relations in a way of non-directional line connecting two entities. To help you to create this chart, we developed ConceptDraw STORE product full of libraries with vector elements you can use for your flowchart. Also we provide you with Solutions section on this site where you can find the numerous stencil libraries, samples and examples to simplify your work with software called ConceptDraw DIAGRAM which is the only one offering that many symbols and templates for making professionally looking smart and mature diagrams.

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FAQs

What are the symbols used in an ERD? ›

Entity Relationship Diagram Symbols & Notations mainly contains three basic symbols which are rectangle, oval and diamond to represent relationships between elements, entities and attributes. There are some sub-elements which are based on main elements in ERD Diagram.

What is the symbol for a relationship in an ERD? ›

ER diagram notations and symbols. Similar to other diagram shapes, in ER diagrams entities are represented with rectangles, attributes are represented by ovals or inside entities, and relationships are shown in diamonds or with lines. There are six notation types, some more common than others.

How many symbols are there in ER diagram? ›

More Questions About ER Diagram Symbols

There are 3 commonly used symbols in entity relationship diagram – Entity, Relationship, and Attribute.

Which symbol represents weak entity in ERD? ›

Weak entity is represented by double rectangle. The relation between one strong and one weak entity is represented by double diamond.

What does an arrow mean in ERD? ›

the simple answer is that it means your two entities who both are part of the same relationship, one instance of them must be part of the relationship but the one who the arrow points towards can exist only once or not at all.

What does triangle represent in ER diagram? ›

Pyramid Diagram

Pyramid diagrams help you visualize information as a triangle divided into horizontal slices. Labelled slices represent a hierarchy. Pyramids are used in marketing presentations to show and analyze hierarchy levels.

How do I make an ERD diagram in Word? ›

Go to the File menu, find Database, choose an ER diagram type and start. The ER diagram symbols library will open automatically on the left, providing a defined set of symbols commonly used in ER diagram. Drag a suitable shape for each entity or primary business concept relevant to your model.

What is entity ERD? ›

An ERD entity is a definable thing or concept within a system, such as a person/role (e.g. Student), object (e.g. Invoice), concept (e.g. Profile) or event (e.g. Transaction) (note: In ERD, the term "entity" is often used instead of "table", but they are the same). When determining entities, think of them as nouns.

What is the symbol of simple attribute? ›

A simple attribute is represented by an oval.

What is the symbol for inheritance? ›

In UML, an inheritance relationship is represented by an arrow with a triangular tip pointing from the derived class to the base class.

What is the symbol for many in a one to many relationship? ›

Relationships can be one-to-one, one-to-many, or many-to-many. The many side is denoted by the crow's foot symbol; one is denoted by a single line. Each entity in a relationship can be mandatory or optional.

What does N stand for in ERD? ›

These primary key might be single attribute like userid in users table or composite primary key (consists of multiple attributes together) like mode_program table. In ERD, U stands for unique in that table and N stands for nullable (can be null).

What is the symbol for inheritance? ›

In UML, an inheritance relationship is represented by an arrow with a triangular tip pointing from the derived class to the base class.

What is the symbol for many in a one to many relationship? ›

Relationships can be one-to-one, one-to-many, or many-to-many. The many side is denoted by the crow's foot symbol; one is denoted by a single line. Each entity in a relationship can be mandatory or optional.

What is a primary key in an ERD? ›

The primary key is a candidate key that is selected by the database designer to be used as an identifying mechanism for the whole entity set. It must uniquely identify tuples in a table and not be null. The primary key is indicated in the ER model by underlining the attribute.

Videos

1. What is an ER diagram? How to make an ERD? What are ERD symbols?
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2. Entity Relationship Diagram - ERD - Conceptual Model - Crow's Foot Notation - Class 5
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3. ER Diagram | Entity Relationship Diagram Tutorial | ER Diagram In DBMS | SQL Tutorial | Simplilearn
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4. How to Draw ER Diagrams | EdrawMax Tutorial
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5. Creating Entity Relationship Diagram (ERD) Using Lucidchart
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6. Create Entity Relationship Diagrams (ERD) with draw.io
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