🎯 What is Entity?
An Entity is any real-world object, concept, or thing that is uniquely identifiable and about which data can be stored in a database.
Entity: An Entity is a “thing” or “object” in the real world that is distinguishable from all other objects
It has physical existence. (e.g: Each student in a college is an entity)
Entity can be uniquely identified. (By a primary attribute, aka Primary Key)
🎯 Example Entities:
In a university database:
🧑🎓
Student📚
Course👨🏫
Teacher
Each of these is something the database needs to track and store information about.
<div class="infographic-entities">
<style>
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@keyframes entities-pulse {
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@media (max-width: 560px) {
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.infographic-entities .record {
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.infographic-entities .record-head {
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.infographic-entities .field-key {
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font-family: var(--mono-font);
font-size: 0.82rem;
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animation: entities-fade-in 0.35s ease forwards;
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@keyframes entities-fade-in {
to { opacity: 1; transform: translateX(0); }
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.infographic-entities .takeaway {
margin-top: 1.5rem;
font-size: 0.88rem;
color: var(--ink-soft);
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.infographic-entities .takeaway strong {
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.infographic-entities .hint {
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text-align: center;
margin-top: 0.6rem;
letter-spacing: 0.02em;
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.infographic-entities .progress-track {
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margin-top: 0.9rem;
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@keyframes entities-progress {
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to { width: 100%; }
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transition-duration: 0.001ms !important;
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</style>
<h2>Entities in a Database</h2>
<p class="subtitle">A university database needs to track and store information about several kinds of things. Each one is an <strong>entity</strong>. Click one to see what it actually stores.</p>
<div class="db-shell">
<div class="db-label">University Database</div>
<div class="compare" role="group" aria-label="Entity types">
<button class="compare-col" type="button" data-entity="student">
<span class="emoji">🧑🎓</span>
<span class="name">Student</span>
<span class="tag">who is learning</span>
</button>
<button class="compare-col" type="button" data-entity="course">
<span class="emoji">📚</span>
<span class="name">Course</span>
<span class="tag">what is taught</span>
</button>
<button class="compare-col" type="button" data-entity="teacher">
<span class="emoji">👨🏫</span>
<span class="name">Teacher</span>
<span class="tag">who is teaching</span>
</button>
</div>
<div class="record" id="entities-record">
<div class="record-head" id="entities-record-head">🧑🎓 Student record</div>
<div class="record-body" id="entities-record-body"></div>
</div>
<div class="progress-track"><div class="progress-fill" id="entities-progress"></div></div>
<div class="hint" id="entities-hint">auto-cycling · click any entity to pause & explore</div>
</div>
<p class="takeaway"><strong>Entity = a real thing the database remembers</strong>, and its fields are the specific facts it keeps about that thing.</p>
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var DATA = {
student: {
head: '🧑🎓 Student record',
fields: [
['student_id', 'STU-2041'],
['name', 'Ananya Rao'],
['email', 'ananya.rao@uni.edu'],
['enrolled_in', 'Data Structures, DBMS']
]
},
course: {
head: '📚 Course record',
fields: [
['course_id', 'CSE-303'],
['title', 'Database Systems'],
['credits', '4'],
['department', 'Computer Science']
]
},
teacher: {
head: '👨🏫 Teacher record',
fields: [
['teacher_id', 'FAC-118'],
['name', 'Dr. Vikram Shah'],
['department', 'Computer Science'],
['teaches', 'CSE-303, CSE-410']
]
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render(key);
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hint.textContent = 'auto-cycling · click any entity to pause & explore';
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</div>.demo {
font-family: system-ui, sans-serif;
padding: 16px;
}
.demo h1 {
color: #2563eb;
margin: 0 0 8px;
}
.demo p {
color: #4b5563;
margin: 0;
}document.querySelector('.demo h1')?.addEventListener('click', () => {
alert('Hello from live preview!');
});🧩 Entity vs Attribute
🧱 Term | 💡 Meaning | 📝 Example |
|---|---|---|
Entity | The object or thing being stored |
|
Attribute | Property/characteristic of the entity |
|
🧬 Types of Entities
🔹 Strong Entity
Exists independently
Has its own primary key
📌 Example:
Student(ID, Name, Age)
🔸 Weak Entity
Cannot exist without a related strong entity
Lacks a primary key on its own
Relies on a foreign key for identification
📌 Example:
Deparment(Dept_Name, Semester, Student_ID)(Here,
Student_IDis a foreign key from theStudententity)
<div class="infographic-entity-types">
<style>
.infographic-entity-types {
--ink: #1a1a1a;
--ink-soft: #5c5c5c;
--paper: #ffffff;
--paper-alt: #f0ece4;
--accent: #2563eb;
--accent-soft:#e3ebfd;
--line: #ddd6c9;
--error: #c0392b;
--error-soft: #fbe9e7;
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font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
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color: var(--ink);
padding: 2rem 1.5rem 2.5rem;
max-width: 780px;
margin: 0 auto;
box-sizing: border-box;
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--ink: #e8e6e1;
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--accent-soft:#202942;
--line: #2c313d;
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--success-soft: #1b3320;
}
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box-sizing: border-box;
}
.infographic-entity-types h2 {
font-size: 1.4rem;
margin: 0 0 0.25rem;
letter-spacing: -0.01em;
}
.infographic-entity-types .subtitle {
color: var(--ink-soft);
font-size: 0.92rem;
margin: 0 0 1.5rem;
max-width: 52ch;
}
.infographic-entity-types .stage {
position: relative;
display: grid;
grid-template-columns: 1fr 1fr;
gap: 2.5rem;
align-items: start;
padding-top: 0.5rem;
}
@media (max-width: 600px) {
.infographic-entity-types .stage { grid-template-columns: 1fr; gap: 2.75rem; }
}
.infographic-entity-types .ent-card {
background: var(--paper-alt);
border: 1px solid var(--line);
border-radius: 12px;
padding: 1.1rem 1rem 1.3rem;
position: relative;
transition: opacity 0.4s ease, transform 0.4s ease, filter 0.4s ease;
}
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font-size: 0.68rem;
text-transform: uppercase;
letter-spacing: 0.08em;
color: var(--accent);
font-weight: 700;
margin-bottom: 0.15rem;
}
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font-weight: 700;
font-size: 1.02rem;
margin-bottom: 0.15rem;
}
.infographic-entity-types .ent-desc {
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color: var(--ink-soft);
margin-bottom: 0.75rem;
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font-family: var(--mono-font);
font-size: 0.78rem;
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font-family: -apple-system, BlinkMacSystemFont, sans-serif;
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font-weight: 700;
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border-radius: 999px;
letter-spacing: 0.03em;
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background: var(--accent-soft);
color: var(--accent);
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color: var(--accent);
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margin-bottom: 0.4rem;
position: relative;
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display: inline-block;
transition: opacity 0.3s ease, filter 0.3s ease;
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@media (max-width: 600px) {
.infographic-entity-types .link-note { display: none; }
}
/* deleted / broken states */
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filter: grayscale(1);
transform: scale(0.97);
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border-color: var(--error);
}
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border-color: var(--success);
}
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margin-top: 0.65rem;
font-size: 0.76rem;
font-weight: 600;
min-height: 1.1em;
}
.infographic-entity-types .status-line.ok { color: var(--ink-soft); }
.infographic-entity-types .status-line.error { color: var(--error); }
.infographic-entity-types .status-line.success { color: var(--success); }
.infographic-entity-types .ent-card.shake {
animation: entity-shake 0.4s;
}
@keyframes entity-shake {
0%, 100% { transform: translateX(0); }
20% { transform: translateX(-5px); }
40% { transform: translateX(5px); }
60% { transform: translateX(-4px); }
80% { transform: translateX(3px); }
}
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display: flex;
justify-content: center;
gap: 0.6rem;
margin-top: 1.6rem;
flex-wrap: wrap;
}
.infographic-entity-types .btn {
font: inherit;
font-size: 0.82rem;
font-weight: 600;
padding: 0.55rem 1rem;
border-radius: 999px;
border: 1px solid var(--line);
background: var(--paper);
color: var(--ink);
cursor: pointer;
transition: background 0.15s, border-color 0.15s, color 0.15s, opacity 0.2s;
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.infographic-entity-types .btn:hover:not(:disabled) {
border-color: var(--accent);
color: var(--accent);
}
.infographic-entity-types .btn.primary {
background: var(--error);
border-color: var(--error);
color: #fff;
}
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opacity: 0.9;
color: #fff;
}
.infographic-entity-types .btn:disabled {
opacity: 0.4;
cursor: not-allowed;
}
.infographic-entity-types .takeaway {
margin-top: 1.5rem;
font-size: 0.88rem;
color: var(--ink-soft);
border-left: 3px solid var(--accent);
padding: 0.5rem 0 0.5rem 0.9rem;
transition: border-color 0.3s ease, color 0.3s ease;
}
.infographic-entity-types .takeaway strong { color: var(--ink); }
.infographic-entity-types .takeaway.is-error {
border-left-color: var(--error);
}
@media (prefers-reduced-motion: reduce) {
.infographic-entity-types *, .infographic-entity-types *::before, .infographic-entity-types *::after {
animation-duration: 0.001ms !important;
transition-duration: 0.001ms !important;
}
}
</style>
<h2>Strong vs Weak Entity</h2>
<p class="subtitle">One of these can stand on its own. The other can't. Delete the parent and watch what actually happens.</p>
<div class="stage">
<div class="ent-card" id="ety-strong">
<div class="ent-kicker">🔹 Strong Entity</div>
<div class="ent-title">Student</div>
<div class="ent-desc">Exists independently · has its own primary key</div>
<div class="schema">
<div class="schema-row"><span>ID</span><span class="badge pk">PK</span></div>
<div class="schema-row"><span>Name</span><span></span></div>
<div class="schema-row"><span>Age</span><span></span></div>
</div>
<div class="status-line ok" id="status-strong">alive</div>
</div>
<div class="ent-card" id="ety-weak">
<div class="ent-kicker">🔸 Weak Entity</div>
<div class="ent-title">Department</div>
<div class="ent-desc">No primary key of its own · identified through Student</div>
<div class="schema">
<div class="schema-row"><span>Dept_Name</span><span></span></div>
<div class="schema-row"><span>Semester</span><span></span></div>
<div class="schema-row" id="row-fk"><span>Student_ID</span><span class="badge fk">FK</span></div>
</div>
<div class="status-line ok" id="status-weak">alive · linked to Student.ID</div>
</div>
<div class="link-note"><span class="chain" id="chain-note">🔗 Student_ID references Student.ID</span></div>
</div>
<div class="controls">
<button class="btn primary" id="btn-delete-student" type="button">🗑️ Delete Student</button>
<button class="btn" id="btn-delete-dependent" type="button">🗑️ Delete Department</button>
<button class="btn" id="btn-reset" type="button" disabled>↺ Reset</button>
</div>
<p class="takeaway" id="ety-takeaway"><strong>Weak entities borrow their identity</strong> from a strong entity — remove the parent, and the dependent has nothing left to point to.</p>
<script>
(function () {
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strongCard.classList.add('is-safe');
takeaway.classList.remove('is-error');
takeaway.innerHTML = '<strong>Student is untouched.</strong> A strong entity never depends on a weak one — the relationship only runs one way.';
}
function reset() {
strongCard.classList.remove('is-deleted', 'is-safe');
weakCard.classList.remove('is-deleted', 'is-orphaned');
rowFk.classList.remove('is-broken');
chainNote.style.opacity = '';
chainNote.style.filter = '';
statusStrong.textContent = 'alive';
statusStrong.className = 'status-line ok';
statusWeak.textContent = 'alive · linked to Student.ID';
statusWeak.className = 'status-line ok';
takeaway.classList.remove('is-error');
takeaway.innerHTML = '<strong>Weak entities borrow their identity</strong> from a strong entity — remove the parent, and the dependent has nothing left to point to.';
btnDeleteStudent.disabled = false;
btnDeleteDependent.disabled = false;
btnReset.disabled = true;
}
btnDeleteStudent.addEventListener('click', deleteStudent);
btnDeleteDependent.addEventListener('click', deleteDependentOnly);
btnReset.addEventListener('click', reset);
})();
</script>
</div>.demo {
font-family: system-ui, sans-serif;
padding: 16px;
}
.demo h1 {
color: #2563eb;
margin: 0 0 8px;
}
.demo p {
color: #4b5563;
margin: 0;
}document.querySelector('.demo h1')?.addEventListener('click', () => {
alert('Hello from live preview!');
});🧠 Summary Table
🔤 Concept | 📖 Description |
|---|---|
Entity | Real-world object to store data about |
Attribute | Describes a property of an entity |
Entity Set | Collection of entities of the same type |
Strong Entity | Independent, has a primary key |
Weak Entity | Depends on another entity, no independent key |