Erd entity relationship diagram symbols and meaning

ERD Symbols and Meanings

erd entity relationship diagram symbols and meaning

Entity - ERD Symbol A weak entity is an entity that must defined by a foreign key relationship with. Use also ConceptDraw DIAGRAM enhanced with powerful Entity-Relationship Diagram (ERD) solution to draw your own ER diagrams using Chen's notation. It is the specialized Entity Relationship diagram symbols, and the meanings of those symbols ERD Symbols and Meaning - Identifying Relationship.

Relationships are meaningful associations between or among entities like assigning, associating, or tracking. Categories are tables that are subtypes of a parent table. In relation to a databasean entity is a single person, place, or thing about which data can be stored. Strong entity is one that exists on its own, independent of other entities.

Weak entity is one whose existence depends on another entity. A weak entity cannot be uniquely identified by its attributes alone.

ERD Symbols and Meanings

Strong relationships are connections that exist between a strong entity type and its owner. Weak relationships are connections that exist between a weak entity type and its owner.

Attribute is a piece of information which determines the properties of a field or tag in a database or a string of characters in a display. When you use the category symbols, you may notice that there is a floating button on the shape.

erd entity relationship diagram symbols and meaning

Click the floating button, you may set the property of the category. Some people may be confused how to use connector to connect entity symbols. Actually, it is easy, you can move the connector towards the shape, then you can find that the entity shape has lots of green marks. Object Relationship Symbols The following picture is the object relationship symbols including entity, relationship, view, parent to category, category to child, table inheritance, type, type inheritance and dynamic connector.

Type of a relationship is created depends upon how related objects are defined. Type inheritance is an additional property offered by hierarchy within structured complex data. Chen ERD Symbols Entity in a database could be a single person, place, or thing about which data can be stored. Aggregation is a special type of association in which objects are assembled or configured together to create a more complex object.

An aggregation describes a group of objects and how you interact with them. One to many N is by far the most common relationship type. Many to many M lets you relate each row in one table to many rows in another table, and vice versa.

What is Entity Relationship Diagram (ERD)?

Many-to-many relationships often hide meaning. Relationship Symbols Composition relationship, which was named composition association relationship in UML 1. A composition relationship specifies that the lifetime of the part classifier is dependent on the lifetime of the whole classifier.

Inheritance relationship helps to communicate structure and inheritance of an object model. So, when do we draw ERDs?

ER Diagram Symbols and Their Usage

While ER models are mostly developed for designing relational database in terms of concept visualization and in terms of physical database design, there are still other situations when ER diagrams can help. Here are some typical use cases.

Database design - Depending on the scale of change, it can be risky to alter a database structure directly in a DBMS. To avoid ruining the data in a production database, it is important to plan out the changes carefully. ERD is a tool that helps.

What is Entity Relationship Diagram (ERD)?

By drawing ER diagrams to visualize database design ideas, you have a chance to identify the mistakes and design flaws, and to make correction before executing the changes in database. Database debugging - To debug database issues can be challenging, especially when the database contains many tables, which require writing complex SQL in getting the information you need. By visualizing a database schema with an ERD, you have a full picture of the entire database schema. You can easily locate entities, view their attributes and to identify the relationships they have with others.

All these allows you to analyze an existing database and to reveal database problem easier. Database creation and patching - ERD tool like Visual Paradigm supports database generation tool that can automate the database creation and patching process by means of ER diagrams.

So, with this ER Diagram tool your ER design is no longer just a static diagram but a mirror that reflects truly the physical database structure. Aid in requirements gathering - Determine the requirements of an information system by drawing a conceptual ERD that depicts the high-level business objects of the system. Such an initial model can also be evolved into physical database model that aids the creation of relational database, or aids in the creation of process map and data flow model.

In this section we will go through the ERD symbols in detail. Studentobject e. Invoiceconcept e. Profile or event e. In ERD, the term "entity" is often used instead of "table", but they are the same.

erd entity relationship diagram symbols and meaning

When determining entities, think of them as nouns. In ER models, an entity is shown as a rounded rectangle, with its name on top and its attributes listed in the body of the entity shape. Entity Attributes Also known as column, an attribute is a property or characteristic of the entity that holds it. An attribute has a name that describes the property and a type that describes the kind of attribute it is, such as varchar for a string, and int for integer.

The ER diagram example below shows an entity with some attributes in it. Primary Key Also known as PK, a primary key is a special kind of entity attribute that uniquely defines a record in a database table. In other words, there must not be two or more records that share the same value for the primary key attribute. The ERD example below shows an entity 'Product' with a primary key attribute 'ID', and a preview of table records in database.

Foreign Key Also known as FK, a foreign key is a reference to a primary key in table. It is used to identify the relationships between entities.