

An ER diagram in DBMS (database management systems) is a lot like a storyboard for an animated TV show – it’s a collection of diagrams that show how everything fits together. Where a storyboard demonstrates the flow from one scene to the next, an ER diagram highlights the components of your databases and the relationships they share.
Understanding the ER model in DBMS is the first step to getting to grips with basic database software (like Microsoft Access) and more complex database-centric programming languages, such as SQL. This article explores ER diagrams in detail.
ER Model in DBMS
An ER diagram in DBMS is a tangible representation of the tables in a database, the relationships between each of those tables, and the attributes of each table. These diagrams feature three core components:
- Entities – Represented by rectangles in the diagram, entities are objects or concepts used throughout your database.
- Attributes – These are the properties that each entity possesses. ER diagrams use ellipses to represent attributes, with the attributes themselves tending to be the fields in a table. For example, an entity for students in a school’s internal database may have attributes for student names, birthdays, and unique identification numbers.
- Relationships – No entity in an ER diagram is an island, as each is linked to at least one other. These relationships can take multiple forms, with said relationships dictating the flow of information through the database.
Mapping out your proposed database using the ER model is essential because it gives you a visual representation of how the database works before you start coding or creating. Think of it like the blueprint you’d use to build a house, with that blueprint telling you where you need to lay every brick and fit every door.
Entities in DBMS
An Entity in DBMS tends to represent a real-life thing (like the students mentioned previously) that you can identify with certain types of data. Each entity is distinguishable from the others in your database, meaning you won’t have multiple entities listing student details.
Entities come in two flavors:
- Tangible Entities – These are physical things that exist in the real world, such as a person, vehicle, or building.
- Intangible Entities – If you can see and feel an entity, it’s intangible. Bank accounts are good examples. We know they exist (and have data attributed to them) but we can’t physically touch them.
There are also different entity strengths to consider:
- Strong Entities – A strong entity is represented using a rectangle and will have at least one key attribute attached to it that allows you to identify it uniquely. In the student example we’ve already shared, a student’s ID number could be a unique identifier, creating a key attribute that leads to the “Student” entity being strong.
- Weak Entities – Weak entities have no unique identifiers, meaning you can’t use them alone. Represented using double-outlined rectangles, these entities rely on the existence of strong entities to exist themselves. Think of it like the relationship between parent and child. A child can’t exist without a parent, in the same way that a weak entity can’t exist without a strong entity.
Once you’ve established what your entities are, you’ll gather each specific type of entity into an entity set. This set is like a table that contains the data for each entity in a uniform manner. Returning to the student example, any entity that has a student ID number, name, and birthdate, may be placed into an overarching “Student” entity set. They’re basically containers for specific entity types.
Attributes in DBMS
Every entity you establish has attributes attached to it, as you’ve already seen with the student example used previously. These attributes offer details about various aspects of the entity and come in four types:
- Simple Attributes – A simple attribute is any attribute that you can’t break down into further categories. A student ID number is a good example, as this isn’t something you can expand upon.
- Composite Attributes – Composite attributes are those that may have other attributes attached to them. If “Name” is one of your attributes, its composites could be “First Name,” “Surname,” “Maiden Name,” and “Nickname.”
- Derived Attributes – If you can derive an attribute from another attribute, it falls into this category. For instance, you can use a student’s date of birth to derive their age and grade level. These attributes have dotted ellipses surrounding them.
- Multi-valued Attributes – Represented by dual-ellipses, these attributes cover anything that can have multiple values. Phone numbers are good examples, as people can have several cell phone or landline numbers.
Attributes are important when creating an ER model in DBMS because they show you what types of data you’ll use to populate your entities.
Relationships in DBMS
As your database becomes more complex, you’ll create several entities and entity sets, with each having relationships with others. You represent these relationships using lines, creating a network of entities with line-based descriptions telling you how information flows between them.
There are three types of relationships for an ER diagram in DBMS:
- One-to-One Relationships – You’ll use this relationship when one entity can only have one of another entity. For example, if a school issues ID cards to its students, it’s likely that each student can only have one card. Thus, you have a one-to-one relationship between the student and ID card entities.
- One-to-Many Relationships – This relationship type is for when one entity can have several of another entity, but the relationship doesn’t work in reverse. Bank accounts are a good example, as a customer can have several bank accounts, but each account is only accessible to one customer.
- Many-to-Many Relationships – You use these relationships to denote when two entities can have several of each other. Returning to the student example, a student will have multiple classes, with each class containing several students, creating a many-to-many relationship.
These relationships are further broken down into “relationship sets,” which bring together all of the entities that participate in the same type of relationship. These sets have three varieties:
- Unary – Only one entity participates in the relationship.
- Binary – Two entities are in the relationship, such as the student and course example mentioned earlier.
- n-ary – Multiple entities participate in the relationship, with “n” being the number of entities.
Your ER diagram in DBMS needs relationships to show how each entity set relates to (and interacts with) the others in your diagram.
ER Diagram Notations
You’ll use various forms of notation to denote the entities, attributes, relationships, and the cardinality of those relationships in your ER diagram.
Entity Notations
Entities are denoted using rectangles around a word or phrase, with a solid rectangle meaning a strong entity and a double-outlined rectangle denoting a weak entity.
Attribute Notations
Ellipses are the shapes of choice for attributes, with the following uses for each attribute type:
- Simple and Composite Attribute – Solid line ellipses
- Derived Attribute – Dotted line ellipses
- Multi-Valued Attribute – Double-lined ellipses
Relationship Notations
Relationship notation uses diamonds, with a solid line diamond depicting a relationship between two attributes. You may also find double-lined diamonds, which signify the relationship between a weak entity and the strong entity that owns it.
Cardinality and Modality Notations
These lines show you the maximum times an instance in one entity set can relate to the instances of another set, making them crucial for denoting the relationships inside your database.
The endpoint of the line tells you everything you need to know about cardinality and ordinality. For example, a line that ends with three lines (two going diagonally) signifies a “many” cardinality, while a line that concludes with a small vertical line signifies a “one” cardinality. Modality comes into play if there’s a minimum number of instances for an entity type. For example, a person can have many phone numbers but must have at least one.
Steps to Create an ER Diagram in DBMS
With the various notations for an ER diagram in DBMS explained, you can follow these steps to draw your own diagram:
- Identify Entities – Every tangible and intangible object that relates to your database is an entity that you need to identify and define.
- Identify Attributes – Each entity has a set of attributes (students have names, ID numbers, birthdates, etc.) that you must define.
- Identify Relationships – Ask yourself how each entity set fits together to identify the relationships that exist between them.
- Assign Cardinality and Modality – If you have an instance from Entity A, how many instances does it relate to in Entity B? Is there a minimum to consider? Assign cardinalities and modalities to offer the answers.
- Finalize Your Diagram – Take a final pass over the diagram to ensure all required entities are present, they have the appropriate attributes, and that all relationships are defined.
Examples of ER Diagrams in DBMS
Once you understand the basics of the ER model in DBMS, you’ll see how they can apply to multiple scenarios:
- University Databases – A university database will have entities such as “Student,” “Teacher,” “Course,” and “Class.” Attributes depend on the entity, with the people-based entities having attributes including names, dates of birth, and ID numbers. Relationships vary (i.e., a student may only have one teacher but a single teacher may have several students).
- Hospital Management Databases – Entities for this type of database include people (“Patients,” “Doctors,” and “Nurses”), as well as other tangibles, such as different hospital buildings and inventory. These databases can get very complex, with multiple relationships linking the various people involved to different buildings, treatment areas, and inventory.
- E-Commerce Databases – People play an important role in the entities for e-commerce sites, too, because every site needs a list of customers. Those customers have payment details and order histories, which are potential entities or attributes. Product lists and available inventory are also factors.
Master the ER Model in DBMS
An ER diagram in DBMS can look like a complicated mass of shapes and lines at first, making them feel impenetrable to those new to databases. But once you get to grips with what each type of shape and line represents, they become crucial tools to help you outline your databases before you start developing them.
Application of what you’ve learned is the key to success with ER diagrams (and any other topic), so take what you’ve learned here and start experimenting. Consider real-world scenarios (such as those introduced above) and draw diagrams based on the entities you believe apply to those scenarios. Build up from there to figure out the attributes and relationships between entity sets and you’re well on your way to a good ER diagram.
Related posts

The Open Institute of Technology (OPIT) began enrolling students in 2023 to help bridge the skills gap between traditional university education and the requirements of the modern workplace. OPIT’s MSc courses aim to help professionals make a greater impact on their workplace through technology.
OPIT’s courses have become popular with business leaders hoping to develop a strong technical foundation to understand technologies, such as artificial intelligence (AI) and cybersecurity, that are shaping their industry. But OPIT is also attracting professionals with strong technical expertise looking to engage more deeply with the strategic side of digital innovation. This is the story of one such student, Obiora Awogu.
Meet Obiora
Obiora Awogu is a cybersecurity expert from Nigeria with a wealth of credentials and experience from working in the industry for a decade. Working in a lead data security role, he was considering “what’s next” for his career. He was contemplating earning an MSc to add to his list of qualifications he did not yet have, but which could open important doors. He discussed the idea with his mentor, who recommended OPIT, where he himself was already enrolled in an MSc program.
Obiora started looking at the program as a box-checking exercise, but quickly realized that it had so much more to offer. As well as being a fully EU-accredited course that could provide new opportunities with companies around the world, he recognized that the course was designed for people like him, who were ready to go from building to leading.
OPIT’s MSc in Cybersecurity
OPIT’s MSc in Cybersecurity launched in 2024 as a fully online and flexible program ideal for busy professionals like Obiora who want to study without taking a career break.
The course integrates technical and leadership expertise, equipping students to not only implement cybersecurity solutions but also lead cybersecurity initiatives. The curriculum combines technical training with real-world applications, emphasizing hands-on experience and soft skills development alongside hard technical know-how.
The course is led by Tom Vazdar, the Area Chair for Cybersecurity at OPIT, as well as the Chief Security Officer at Erste Bank Croatia and an Advisory Board Member for EC3 European Cybercrime Center. He is representative of the type of faculty OPIT recruits, who are both great teachers and active industry professionals dealing with current challenges daily.
Experts such as Matthew Jelavic, the CEO at CIM Chartered Manager Canada and President of Strategy One Consulting; Mahynour Ahmed, Senior Cloud Security Engineer at Grant Thornton LLP; and Sylvester Kaczmarek, former Chief Scientific Officer at We Space Technologies, join him.
Course content includes:
- Cybersecurity fundamentals and governance
- Network security and intrusion detection
- Legal aspects and compliance
- Cryptography and secure communications
- Data analytics and risk management
- Generative AI cybersecurity
- Business resilience and response strategies
- Behavioral cybersecurity
- Cloud and IoT security
- Secure software development
- Critical thinking and problem-solving
- Leadership and communication in cybersecurity
- AI-driven forensic analysis in cybersecurity
As with all OPIT’s MSc courses, it wraps up with a capstone project and dissertation, which sees students apply their skills in the real world, either with their existing company or through apprenticeship programs. This not only gives students hands-on experience, but also helps them demonstrate their added value when seeking new opportunities.
Obiora’s Experience
Speaking of his experience with OPIT, Obiora said that it went above and beyond what he expected. He was not surprised by the technical content, in which he was already well-versed, but rather the change in perspective that the course gave him. It helped him move from seeing himself as someone who implements cybersecurity solutions to someone who could shape strategy at the highest levels of an organization.
OPIT’s MSc has given Obiora the skills to speak to boards, connect risk with business priorities, and build organizations that don’t just defend against cyber risks but adapt to a changing digital world. He commented that studying at OPIT did not give him answers; instead, it gave him better questions and the tools to lead. Of course, it also ticks the MSc box, and while that might not be the main reason for studying at OPIT, it is certainly a clear benefit.
Obiora has now moved into a leading Chief Information Security Officer Role at MoMo, Payment Service Bank for MTN. There, he is building cyber-resilient financial systems, contributing to public-private partnerships, and mentoring the next generation of cybersecurity experts.
Leading Cybersecurity in Africa
As well as having a significant impact within his own organization, studying at OPIT has helped Obiora develop the skills and confidence needed to become a leader in the cybersecurity industry across Africa.
In March 2025, Obiora was featured on the cover of CIO Africa Magazine and was then a panelist on the “Future of Cybersecurity Careers in the Age of Generative AI” for Comercio Ltd. The Lagos Chamber of Commerce and Industry also invited him to speak on Cybersecurity in Africa.
Obiora recently presented the keynote speech at the Hackers Secret Conference 2025 on “Code in the Shadows: Harnessing the Human-AI Partnership in Cybersecurity.” In the talk, he explored how AI is revolutionizing incident response, enhancing its speed, precision, and proactivity, and improving on human-AI collaboration.
An OPIT Success Story
Talking about Obiora’s success, the OPIT Area Chair for Cybersecurity said:
“Obiora is a perfect example of what this program was designed for – experienced professionals ready to scale their impact beyond operations. It’s been inspiring to watch him transform technical excellence into strategic leadership. Africa’s cybersecurity landscape is stronger with people like him at the helm. Bravo, Obiora!”
Learn more about OPIT’s MSc in Cybersecurity and how it can support the next steps of your career.

Open Institute of Technology (OPIT) masterclasses bring students face-to-face with real-world business challenges. In OPIT’s July masterclass, OPIT Professor Francesco Derchi and Ph.D. candidate Robert Mario de Stefano explained the principles of regenerative businesses and how regeneration goes hand in hand with growth.
Regenerative Business Models
Professor Derchi began by explaining what exactly is meant by regenerative business models, clearly differentiating them from sustainable or circular models.
Many companies pursue sustainable business models in which they offset their negative impact by investing elsewhere. For example, businesses that are big carbon consumers will support nature regeneration projects. Circular business models are similar but are more focused on their own product chain, aiming to minimize waste by keeping products in use as long as possible through recycling. Both models essentially aim to have a “net-zero” negative impact on the environment.
Regenerative models are different because they actively aim to have a “net-positive” impact on the environment, not just offsetting their own use but actively regenerating the planet.
Massive Transformative Purpose
While regenerative business models are often associated with philanthropic endeavors, Professor Derchi explained that they do not have to be, and that investment in regeneration can be a driver of growth.
He discussed the importance of corporate purpose in the modern business space. Having a strong and clearly stated corporate purpose is considered essential to drive business decision-making, encourage employee buy-in, and promote customer loyalty.
But today, simple corporate missions, such as “make good shoes,” don’t go far enough. People are looking for a Massive Transformational Purpose (MTP) that can take the business to the next level.
Take, for example, Ben & Jerry’s. The business’s initial corporate purpose may have been to make great ice cream and serve it up in a way that people will enjoy. But the business really began to grow when they embraced an MTP. As they announced in their mission statement, “We believe that ice cream can change the world.” Their business activities also have the aim of advancing human rights and dignity, supporting social and economic justice, and protecting and restoring the Earth’s natural systems. While these aims are philanthropic, they have also helped the business grow.
RePlanet
Professor Derchi next talked about RePlanet, a business he recently worked to develop their MTP. Founded in 2015, RePlanet designs and implements customized renewable energy solutions for businesses and projects. The company already operates in the renewable energy field and ranked as the 21st fastest-growing business in Italy in 2023. So while they were already enjoying great success, Derchi worked with them to see if actively embracing a regenerative business model could unlock additional growth.
Working together, RePlanet moved towards an MTP of building a greener future based on today’s choices, ensuring a cleaner world for generations. Meeting this goal started with the energy products that RePlanet sells, such as energy systems that recover heat from dairy farms. But as the business’s MTP, it goes beyond that. RePlanet doesn’t just engage suppliers; it chooses partners that share its specific values. It also influences the projects they choose to work on – they prioritize high-impact social projects, such as recently installing photovoltaic energy systems at a local hospital in Nigeria – and how RePlanet treats its talent, acknowledging that people are the true energy of the company.
Regenerative Business Strategies
Based on work with RePlanet and other businesses, Derchi has identified six archetypal regenerative business strategies for businesses that want to have both a regenerative impact and drive growth:
- Regenerative Leadership – Laying the foundation for regeneration in a broader sense throughout the company
- Nature Regeneration – Strategies to improve the health of the natural world
- Social Regeneration – Regenerating human ecosystems through things such as fair-trade practices
- Responsible Sourcing – Empowering and strengthening suppliers and their communities
- Health & Well-being – Creating products and services that have a positive effect on customers
- Employee Focus – Improve work conditions, lives, and well-being of employees.
Case Studies
Building on the concept of regenerative business models, Roberto Mario de Stefano shared other case studies of businesses that are having a positive impact and enjoying growth thanks to regenerative business models and strategies.
Biorfarm
Biorfarm is a digital platform that supports small-scale agriculture by creating a direct link between small farmers and consumers. Cutting out the middleman in modern supply chains means that farmers earn about 50% more for their produce. They set consumers up as “digital farmers” who actively support and learn about farming activities to promote more conscious food consumption.
Their vision is to create a food economy in which those who produce food and those who consume it are connected. This moves consumers from passive cash cows for large corporations that prioritize profits over the well-being of farmers to actively supporting natural production and a more sustainable system.
Rifo Lab
Rifo Lab is a circular clothing brand with the vision of addressing the problem of overproduction in the clothing industry. Established in Prato, Italy, a traditional textile-producing area, the company produces clothes made from textile waste and biodegradable materials. There are no physical stores, and all orders must be placed online; everything is made to order, reducing excess production.
With an eye on social regeneration, all production takes place within 30 kilometers of their offices, allowing the business to support ethical and local production. They also work with companies that actively integrate migrants into the local community, sharing their local artisan crafts with future generations.
Ogyre
Ogyre is a digital platform that allows you to pay fishermen to fish for waste. When fishermen are out conducting their livelihood, they also collect a significant amount of waste from the ocean, especially plastic waste. Ogyre arranges for fishermen to get paid for collecting that waste, which in turn supports the local fishing communities, and then transforms the waste collected into new sustainable products.
Moving Towards a Regenerative Future
The masterclass concluded with a Q&A session, where it explained that working in regenerative businesses requires the same skills as any other business. But it also requires you to embrace a mindset where value comes from giving and that growth is about working together for a better future, and not just competition.
Have questions?
Visit our FAQ page or get in touch with us!
Write us at +39 335 576 0263
Get in touch at hello@opit.com
Talk to one of our Study Advisors
We are international
We can speak in: