What is ER Diagrams in DBMS
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ER Diagrams

In software engineering, an entity relational model is an abstract and conceptual representation of data entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema or semantic data model of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created by this process are called entity-relationship diagrams, ER diagrams, or ERDs.

In 1976, the Entity-relationship model developed by Chen, ER Model is a high-level Conceptual model which used Conceptual design of database where relational models are used to logical design of database

ER Diagram

  • A database can be modeled as A collection of entities Relationship among the entities
  • An entity is a real-world object that exists and is distinguishable from other entities Example Person, company, event, plant
  • All the entities in the data model have attributes as known as properties of an entities Example: people have names and addresses An Entity set is a set of entities of all same type that share the same properties. Example: a set of all persons , companies, trees, holidays

ER Diagram enter image description here

Strong Entity type

An entity type that has its own distinct primary key that used to identify specific uniquely from another entity type is called as Strong Entity type

An Entity type that is independent of some other entity type I called Strong Entity type

Example In the case of the Client entity, Client_no is the primary key of Client an entity which is used to uniquely identify among the Client‘s entity set In the case of Customer Entity, Customer_id is the primary key of Customer Entity which is used to uniquely identify among the Customer’s entity set The strong Entity type is represented by rectangle Symbol

Weak entity Type

Entity type which is dependent on some other entity type is called as Weak entity type

  • The weak entity type is dependent on a strong entity and cannot exist on its own
  • It does not have a unique identifier that has a partial identifier
  • The partial identifier is represented by double-line


Properties of an entity or relationship type are called as attribute Example Staffno, staffname,staff_designation is describes an entity Staff Value of an attribute plays a major role in data stored in the database, Each entity will have the value which is assigned to its attributes

Consider an example Above stated example of a Staff Entity that has the attribute named as staffno, the value which is assigned to the staff attribute is ‘101’ and the staffname attribute has the value is ‘Mahendra, and staff_desigination attribute has the value is ‘Manager’

Attribute domains

The set of allowable values which is assigned to one or more attribute is knowns as Attribute domains There are types of attributes that have been classified Such as simple and Composite type, single-valued and multi-valued attributes Stored and derived attributes, null attributes, and Key attributes.

1) Simple Attributes

The simple attribute is an attribute that can be further divided in to two parts Or An Attribute composed of a single component with an independent existence For example Designation of staff and Salary of a staff

Composite Attribute

Composite Attribute is an attribute that is further divided into many parts Or An attributed composed of multiple components, each the component has its own independent existence Example Address attributes of a Branch entity that can be further divided into sub-parts i.e street, city, and postal code as an attributes.

2) Single valued and Multi-Valued attributes

The single-valued attribute is an attribute in which a single value(atomic) for each entity. Or An attribute that holds a single value for each occurrence of an entity type Example: Each branch has only single-valued attributes is known as branch_no

Multi-valued attributes

The multi-valued attribute is an attribute which as many values for each entity Or An attribute that holds multiple values for each occurrence of an entity type. Example: Each staff member has multiple mobile numbers

3) Stored and Derived attributes

The stored attribute is an attribute that is used to supply a value to the related attribute Example Date_of_Birth of staff is a stored attribute

Derived attributes

The value from the derived attribute is derived from the stored attribute for example Date_of_Birth is a stored attribute for each staff member. The value for an Age can be derived from the Date_of_ Birth attributes I.e by subtracting the Date_of _Birth from the Current date, therefore the Stored attributes is used supplied a value to the related attributes

Null attribute

The attribute which takes NULL value when the entity does not have the value to it. The Null attribute is an attribute their value is unknown, unassigned and missing information

Key Attributes

This attribute has the unique value for an entity that is used to Identifying given row in the table is called a key attribute of an entity Example: Staff_ no is a key attribute that has a unique value which is used to identify a given row in the table


  • A primary aim of the database system is to provide a convenient and efficient way to store and retrieve data stored in a database.
  • A database is a computer-generated software program that can be used to access the data stored in the database in an organized manner.
  • The term database is a structured collection of data stored which can be stored in digital form. Before the actual data is stored in the database, we should clearly specify the schema of the database and different techniques used to manipulate the data stored in a database.
  • Database shouldn’t only care about the insertion and modification of the data in the database. At times, it should also focus on how to protect the data stored in the database from unauthorized access.
  • DBMS must provide efficient techniques in order to protect the data from accidental system crashes.
  • If the data has to be shared among a number of users there are highly chances that the data might not remain consistent because too many users might try to access it at the same time and may try to change the value.
  • The DBMS must ensure that the chances of getting anomalous results when the data is used by more than one set of users. DBMS systems can be used extensively in the following fields

    1. Transportation: DBMS system can be used for reservation or cancellation of tickets and can be also used to check for the schedules of incoming and outgoing flights.

    2. Education: DBMS system can be used by different universities to allow students take admission online, check the status of vacant seats, the enrolment system can be done computerized, etc.

    3. Banking: DBMS systems have completely changed the face of the banking sector. A few decades ago, the banking system was purely paper-based systems has now transformed in keeping less paper work.

    4. Sales: DBMS system allows the data to be stored in electronic format by making use of relational databases which allows the data to be stored in a highly organized manner. This database allows the information such as information about the customers, products, sales, purchases etc to be stored in database.
    5. Manufacturing: DBMS system allows the user to store information about the production of good, the inventory details, the total number of orders, supply chain information in database so that it allows the decision makers to make critical decisions in timely manner.
    6. Human Resource: DBMS has made the life of HR team much better by allowing the team to compute tax deductions, employee wages, retrieving the details of the employees in faster manner as compared to traditional paper based approach which was time consuming.

Thus the growth of DBMS system has not only benefitted only to the customers or employees in an organisation but it has touched all the aspects of our lives.

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