Entity relationship diagram in database management system

entity relationship diagram in database management system

ER Model is used to model the logical view of the system from data perspective which consists of these components: Entity, Entity Type, Entity Set –. An Entity. An entity-relationship (ER) diagram is a graphical representation of entities and in regard to the organization of data within databases or information systems. Creating ER Diagram Representation in DBMS. ER Diagram is a visual representation of data using the ER Model, describing how data is modelled.

What is Entity Relationship Diagram (ERD)?

For that, weak entity sets need to have participation. Let's learn more about a weak entity by comparing it with a Strong Entity Strong Entity Set Strong entity set always has a primary key.

It does not have enough attributes to build a primary key. It is represented by a rectangle symbol. It is represented by a double rectangle symbol. It contains a Primary key represented by the underline symbol. It contains a Partial Key which is represented by a dashed underline symbol. The member of a strong entity set is called as dominant entity set. The member of a weak entity set called as a subordinate entity set. Primary Key is one of its attributes which helps to identify its member.

In a weak entity set, it is a combination of primary key and partial key of the strong entity set.

entity relationship diagram in database management system

In the ER diagram the relationship between two strong entity set shown by using a diamond symbol. The relationship between one strong and a weak entity set shown by using the double diamond symbol. The connecting line of the strong entity set with the relationship is single.

The line connecting the weak entity set for identifying relationship is double.

ER Diagram Tutorial in DBMS (with Example)

Attributes It is a single-valued property of either an entity-type or a relationship-type. For example, a lecture might have attributes: An attribute is represented by an Ellipse Types of Attributes Description Simple attribute Simple attributes can't be divided any further.

For example, a student's contact number. It is also called an atomic value. Composite attribute It is possible to break down composite attribute.

For example, a student's full name may be further divided into first name, second name, and last name.

ER Diagram Tutorial in DBMS (with Example)

Derived attribute This type of attribute does not include in the physical database. 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.

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 relationship diagram in database management system

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.

DBMS - Entity Relationship Diagram

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.

entity relationship diagram in database management system

It is used to identify the relationships between entities. Note that foreign keys need not to be unique. Multiple records can share the same values. The ER Diagram example below shows an entity with some columns, among which a foreign key is used in referencing another entity. Relationship A relationship between two entities signifies that the two entities are associated with each other somehow. For example, student might enroll into a course. The entity Student is therefore related with Course, and the relationships is presented as a connector connecting between them.

Cardinality Cardinality defines the possible number of occurrence in one entity which are associated to the number of occurrences in another.

What is Entity Relationship Diagram (ERD)?

When present in an ERD, the entities Team and Player are inter-connected with a one-to-many relationship. In an ER diagram, cardinality is represented as a crow's foot at the connector's ends. The three common cardinal relationships are one-to-one, one-to-many, and many-to-many. One-to-One cardinality example A one-to-one relationship is mostly used to split an entity in two to provide information concisely and make it more understandable. The figure below shows an example of one-to-one relationship.

One-to-Many cardinality example A one-to-many relationship refers to the relationship between two entities X and Y in which an instance of X may be linked to many instances of Y, but an instance of Y is linked to only one instance of X. The figure below shows an example of one-to-many relationship. Many-to-Many cardinality example A many-to-many relationship refers to the relationship between two entities X and Y in which X may be linked to many instances of Y and vice versa.