What does ER diagram represent?

What does ER diagram represent?

An entity relationship diagram (ERD), also known as an entity relationship model, is a graphical representation that depicts relationships among people, objects, places, concepts or events within an information technology (IT) system.

Is a symbol of entity set in ER diagram?

An Entity is an object of Entity Type and set of all entities is called as entity set. e.g.; E1 is an entity having Entity Type Student and set of all students is called Entity Set. In ER diagram, Entity Type is represented as: Attribute(s):

How does an entity set is represented?

A single rectangle is used for the representation of a strong entity set. A double rectangle is used for the representation of a weak entity set. It contains sufficient attributes to form its primary key. A diamond symbol is used for the representation of the relationship that exists between the two strong entity sets.

Is an ER diagram attributes are represented by?

Attributes are represented by ellipses. Ellipses are name with attribute name and connected with rectangle (entity).

How are roles specified in an ER diagram?

Roles can be specified in an ER diagram by labelling the lines. 6. How is the discriminator of a weak entity set specified? Explanation: A discriminator of a weak entity set can be specified by underlining it with a dashed line.

What is the use of ER diagram?

Database troubleshooting: ER diagrams are used to analyze existing databases to find and resolve problems in logic or deployment. Drawing the diagram should reveal where it’s going wrong. Business information systems: The diagrams are used to design or analyze relational databases used in business processes.

What is associative entity in ER diagram?

An associative entity is a term used in relational and entity–relationship theory. A relational database requires the implementation of a base relation (or base table) to resolve many-to-many relationships. A base relation representing this kind of entity is called, informally, an associative table.

How can we identify entity in ER diagram?

An entity must possess a set of one or more attributes that uniquely identify it (called a primary key). The entities on an Entity-Relationship Diagram are represented by boxes (i.e., rectangles). The name of the entity is placed inside the box. Identifying entities is the first step in Data Modelling.

How are the elements in ER model are represented draw and name the elements?

There are three basic elements in an ER Diagram: entity, attribute, relationship. They are weak entity, multi valued attribute, derived attribute, weak relationship, and recursive relationship. Cardinality and ordinality are two other notations used in ER diagrams to further define relationships.

What is ER model in Rdbms?

ER model stands for an Entity-Relationship model. It is a high-level data model. This model is used to define the data elements and relationship for a specified system. In ER modeling, the database structure is portrayed as a diagram called an entity-relationship diagram.

Which of the following is represented by an ER diagram?

1. Which of the following symbols represent entity sets in an ER diagram? Explanation: Rectangles divided into two parts represent entity sets in an ER diagram.

What is an entity set?

An entity set is a group of similar entities and these entities can have attributes. In terms of DBMS, an entity is a table or attribute of a table in database, so by showing relationship among tables and their attributes, ER diagram shows the complete logical structure of a database.

What do you mean by Entity Relationship Diagram?

Entity Relationship Diagram, also known as ERD, ER Diagram or ER model, is a type of structural diagram for use in database design. An ERD contains different symbols and connectors that visualize two important information: The major entities within the system scope, and the inter-relationships among these entities.

How are attributes indicated in an E-R diagram?

B. Attribute:- Each entity has a set of properties. These properties of each entity are termed as attributes. For example, a car entity would be described by attributes such as price, registration number, model number, color etc. Attributes are indicated by ovals in an e-r diagram.

Which is the weak entity in the ER diagram?

The weak entity is shown by a rectangle in an ER diagram. But, the attributes of weak entity set are underlined with the dashed line. The relationship of a weak entity set and strong entity set is shown with the double diamond as shown in the figure below:

What does a diamond represent in an E-R diagram?

A diamond is used to symbolically represent a relationship in the e-r diagram. a). Degree of relationship:- It signifies the number of entities involved in a relationship. Degree of a relationship can be classified into following types: Unary relationship:- If only single entity is involved in a relationship then it is a unary relationship.