Online Library Management System ER Diagram in Software Engineering

Description of an ER Diagram

The relationship between entity sets that are kept in a database is depicted in a diagram known as an entity relationship diagram, or ER Diagram. Alternatively, ER diagrams help to describe the logical organisation of databases. The three basic concepts that lay the groundwork for ER diagrams are entities, characteristics, and relationships.

Rectangles are used to represent entities in ER Diagrams, ovals are used to indicate attributes, and diamond shapes are used to represent relationships.

An ER diagram and a flowchart initially have a similar appearance. However, ER Diagram is a distinctive model because of the numerous specific symbols and their meanings. The entity framework architecture is represented by the ER Diagram.

Description of an ER Model

Entity Relationship Model, or ER Model, is a high-level conceptual data model diagram. To create a well-designed database, rigorous analysis of the data requirements is assisted by the ER model. The ER Model depicts actual people, things, and the connections between them. Before deploying your database, it is recommended that you create an ER Model in a DBMS.

You can create a well-designed database by using ER Modelling to methodically assess your data requirements. Therefore, finishing ER modelling before implementing your database is regarded as best practice.

History of ER models

ER diagrams are useful visual representations of the ER paradigm. In order to establish a standard convention that can be applied to relational databases and networks, Peter Chen introduced the ER Diagram in 1971. He intended to apply a conceptual modelling strategy based on an ER model.

Why Use the ERDiagrams?

These are the main justifications for using the ER Diagram.

  • helps in the definition of terminologies used in entity relationship modelling
  • Give a glimpse of how your tables should connect and what fields each table will have.
  • Description of entities, properties, and relationships is aided by.
  • Because ER diagrams can be converted into relational tables, building databases fast is possible.
  • Database designers might utilise ER diagrams as a guide for implementing data in certain software applications.
  • With the aid of an ERP diagram, the database designer is better able to comprehend the data that will be stored in the database.
  • You can communicate with users about the logical structure of the database using an ERD Diagram.

Information on ER Diagram Model

Let's look at some fascinating information regarding the ER Diagram Model in this ERD Diagram Tutorial:

  • Using the ER model, you can create a database design.
  • It is a popular graphical tool for modelling data that is simple to use.
  • Widely used in Database Design
  • It is a GUI representation of a database's logical structure.
  • It aids in the identification of the entities present in a system and their relationships.

ER Schematics Notations & Symbols

Diagram of an entity relationship Three basic symbols—the rectangle, oval, and diamond—are used primarily in Symbols & Notations to describe relationships between elements, entities, and properties. In the ERD Diagram, several sub-components are based on the major elements.Using various ERD Symbols and Notations, an ER Diagram is a visual representation of data that shows how data are related to one another.

The primary elements and their symbols in ER Diagrams are as follows:

  • Rectangles: This entity type symbol is used in entity relationship diagrams.
  • Ellipses: Symbols for qualities
  • Diamonds: Relationship kinds are represented by this symbol.
  • Lines: It connects entity types with other relationship types and attributes to entity types.
  • Primary key: highlighted qualities
  • Ellipses twice: Represent properties with multiple values

Items in the ER Diagram

Three fundamental ideas form the basis of this model:

  • Entities
  • Attributes
  • Relationships
  • ER Diagram Examples

For instance, we might have entities for students, courses, and lecturers in a university database. Attributes for the students entity are Rollno, Name, and DeptID. They might be connected to certain Lecturers and Courses.

What is an Entity?

a tangible object, living or not, that is both easily identifiable and unrecognisable. Everything that has to be reflected in our database belongs to the business. It may be something tangible, just a fact about the company, or even something that actually occurs in the real world.

An entity is a type of data storage in a database that can be a place, person, thing, event, or concept. Entities need to have a key that is distinct and an attribute. Every entity is made up of a few "attributes" that define it.

Examples of Entities:

  • Person: Workers, students, or clients
  • Location: Shop, Building
  • Object: Car, Product, and Machine
  • Event: Purchase, Sign-Up, and Renewal
  • Concept: Account, Course

Entity set


A collection of entities of the same kind is known as an entity set. It might include entities whose attributes have values that are similar. Properties, usually referred to as attributes, are used to represent entities. Each characteristic has a unique value. A student entity, for instance, might have a name, age, and class as properties.

Instances of Entities

There could be some departments at a university. These departments all provide a variety of curricula and employ a variety of professors.

Each programme is composed of a few courses. Students sign up for a certain programme and sign up for various courses inside it. Each course is taught by a lecturer from the designated department, who teaches a different group of students.


The definition of a relationship is simply the association of two or more entities. Tom, for instance, works in the Chemistry division.

Relationships between entities occur. With verbs or verb phrases, we can frequently find relationships.

  • You're taking part in this lecture.
  • I'm the one giving the lecture.
  • Similar to entities, relationships can be categorised based on several sorts of relationships:
  • Attending a lecture as a student
  • Giving a lecture is a lecturer.

Weak Entities

An entity that lacks its primary attribute is referred to as weak. By taking into account the main key of another entity, it can be uniquely identified. Weak entity sets must be involved in order for that to happen.

"Trans No" is a discriminator within a group of transactions in an ATM in the ER Diagram examples above.

Comparing a weak entity to a strong entity will help us understand a weak entity better.

Strong Entity SetWeak Entity Set
A primary key is always present in a strong entity set.There are not enough attributes to create a primary key.
The symbol for it is a rectangle.The symbol for it is a double rectangle.
A Primary key is present, and that key is denoted by the underline.It contains a partial key, shown by the symbol of a dashed underline.
A dominating entity set is one that contains members of a strong entity set.The constituent of what is known as a subordinate entity set.
One of its characteristics that aids in member identification is Primary Key.It combines the primary key and a portion of the key from the strong entity set in a weak entity set.
The relationship between two strong entities is represented by a diamond symbol in the ER diagram.The double diamond symbol represents the link between one powerful entity and one weak entity.
The relationship between the strong entity set and it is connected by a single line.For detecting relationships, there is a double line connecting the weak entity set.


It is a relationship-type or entity-type single-valued property.

A lecture, for instance, might have the following attributes: time, date, duration, location, etc.

Types of Attributes            Description
Simple attributeSimple characteristics cannot be subdivided further. a student's phone number, as an illustration. Another name for it is an atomic value.
Composite attributeAn attribute called composite can be broken down. A student's whole name, for instance, might be broken down into first name, second name, and last name.
Derived attributeThis kind of attribute is not present in the actual database. However, the values of these attributes are obtained from other database attributes. Age, for instance, shouldn't be stored directly. Instead, it ought to be calculated using the employee's DOB.
Multivalued attributeMultivalued characteristics allow for the existence of several values. For instance, a student is allowed to have many email addresses, mobile numbers, etc.

The above section was brief description about ER diagram. Now, let us discuss about ER Diagram of Online Library Management System.

The many operations of the library are handled by the automated library system known as the online library management system. The library management software is fully addressed by it. Bar code systems and RFID systems are the two categories under which the online library management system is categorised.

Every school and college has a library, and without Library Administration Software, there wouldn't be any schools or colleges. Every school and college should have one since it helps the library keep track of the books that are available and those that have been released. By giving students the opportunity to learn, gather resources, encourage group learning, and advance knowledge and abilities, library management system software benefits students in a variety of ways.

Specifications of an online library management system

  • including all student records
  • Organize the records in a methodical way.
  • Any information can be tracked online.
  • The reports can be produced.
  • Organize all data online.
  • Maintaining records is simple
  • It enables quick book entry

With the development of the system, there is a rising demand for library automation software in India. Everyone likes rapid and precise service because we all live in the digital age. Due to its ordered and methodical database management, almost all schools and universities favour the library management system. Students can easily and quickly prepare their projects with the aid of college library software. It also aids in the creation of assignments and notes.

By facilitating quick access to the library system, library management systems aid students in studying more effectively. With the use of Advance Library Software, they can quickly locate publications, catalogues, and books of interest.

Advantages of Online Library Management System

Following are the benefits of an online library management system:

  • The software is user-friendly.
  • It aids in record keeping and is inexpensive and simple to install.
  • This method makes it possible to track any information, which improves efficiency.
  • It decreases the likelihood of error while saving time and human effort.
  • It has anti-theft properties.

The Online Library Management System is divided into two categories: bar code system and RFID system, as was previously mentioned. Every book in a bar code system is given a special bar code number, and with the use of a bar code reader, we may find out information about the book's status, such as when it was issued and returned.The RFID-based library management system,on the other hand, is a wireless system that makes it simple to maintain records, lessens the workload of a librarian, and speeds up the tracking of data.

Every piece of information is kept in an organized, systematic manner using a library management system, producing successful outcomes. The habit of silent reading is formed, and the students' overall performance is improved. The library automation system will be brought up to date thanks to the software, which is also intended to assist students in getting the most out of it.

Entity-Relationship Diagrams, also referred to as ER Diagrams, are used to examine the database's organisational structure. It demonstrates the connections between entities and their characteristics. An ER Model gives people a way to communicate.

The following factors are taken into account while tracking readers in the Library Management System database:

  • With a single point authentication system that consists of a login ID and password, the system keeps track of the staff.
  • The staff updates the book catalogue with information on each title's ISBN, price in Indian rupees, category (novel, general, story), edition, and author number.
  • A publisher has a publisher ID, the name of the book, and the year it was published.
  • Users register by providing a user ID, email address, name (first and last names), phone number (multiple entries are permitted), and communication address. The staff monitors readers.
  • Books that have the issue date and return date stamped can be returned or reserved by readers. It can have a due date as well if it is not returned within the allotted time frame.
  • Staff members also create the reports that include information about returns and issues, readers' IDs, and report the registration numbers.

The major elements of the Library are shown in this ER diagram, including the employees, readers, books, publishers, reports, and authentication system. It makes it possible to comprehend the connections between different items.

Entities and their Attributes

  • Book Entity: Title, edition, category, price, author, and isbn number are all present. The primary key for books is their ISBNs.
  • Reader Entity: There are UserId, Email, Address, Phone, and Name fields. Name is a composite attribute made up of the first and last names. Multi-valued attribute for phone number. The primary key for the Readers entity is UserId
  • Publisher Entity: It has a name, a PublisherId, and a publication year. AuthorID serves as the primary key.
  • Authentication System Entity: LoginId serves as the primary key, and there is also a password.
  • Reports Entity: It contains UserId, Reg no, Book no, and Issue/Return dates. The reports entity's Primary Key is Reg no.
  • Staff Entity: Staff id is the primary key, and it contains both name and staff id.
  • Reserve/Return Relationship Set: The three characteristics are Reserve date, due date, and Return date.

Relations among Entities

  • N books may be reserved by one reader, but only one reader may reserve any given book. 1:N is the relationship.
  • A publisher may release numerous books, but a book is only released by one publisher. 1:N is the relationship.
  • The staff monitors readers. It is a M:N connection.
  • The staff keeps several reports current. 1:N is the relationship.
  • The staff updates several books. 1:N is the relationship.
  • Multiple staff members can log in using the authentication mechanism. 1:N is the relationship.