Introduction to Data Structures: Terminology and Classification: quick revision, 15 bites

Data Structures Are Classified in Two Ways

Two lenses classify every data structure.

Every data structure can be classified along **two independent axes** — by whether it is built into the language, and by how its elements are arranged.

Takeaway. Classification answers two questions: is it built-in, and how are its elements arranged?

Primitive Data Structures: The Building Blocks

The raw bricks of every program.

Takeaway. Primitive structures are the language's built-in single-value types — the raw materials for everything else.

Non-Primitive Data Structures: Built From Primitives

Complex structures grown from simple types.

Takeaway. Non-primitive structures are user-defined groupings built on top of primitive types.

Primitive vs Non-Primitive: Side by Side

Built-in or built-up? Know the difference.

Takeaway. Primitive types store one value; non-primitive types organize many values into a structure.

Linear vs Non-Linear: How Elements Are Arranged

One line, or many branches?

Non-primitive data structures split further by **how their elements are arranged** — in a single sequence, or in a hierarchy.

Takeaway. Linear structures are sequential; non-linear structures are hierarchical.

Spotting the Category in Real Code

Name the type in one glance.

Takeaway. A single built-in variable is primitive; a collection like an array is non-primitive and linear.

Full Classification Map at a Glance

One table, the whole classification.

Takeaway. Primitive has no sub-types; non-primitive splits into linear and non-linear.

Non-Primitive Splits Into Two Groups

Non-primitive isn't the end of the story.

Takeaway. The linear/non-linear split applies only to non-primitive structures, not to primitive ones.

Don't Call an Array Primitive

Arrays are not primitive — here's why.

Takeaway. If it holds multiple values or is derived from basic types, it is non-primitive.

How to Classify Any Data Structure

Three questions, instant classification.

Takeaway. Classify in order: primitive first, then linear vs non-linear for non-primitive.

Where Each Type Shows Up in Real Systems

From undo buttons to maps.

Takeaway. Choosing the right structure — linear or non-linear — decides how efficiently a real system runs.

Remember the Split With 'P-N-L-N'

Four letters, full classification.

Recall the hierarchy as **P → N → L → N**: **P**rimitive, then **N**on-primitive, which splits into **L**inear and **N**on-linear.

Takeaway. P-N-L-N chains the entire classification in order.

Exam Favourite: Give Examples With Each Category

Examiners want examples, not just names.

Takeaway. Category + example + linear/non-linear label = full marks.

Primitive Types Differ Across Languages

Same idea, different names.

The **set of primitive types** is not identical in every language — for example, some languages treat strings as primitive while others treat them as non-primitive. The **classification idea stays the same**, but the exact list can vary.

Takeaway. The primitive/non-primitive concept is universal, but the exact primitive list is language-dependent.

What You Need Before Going Deeper

Lock these basics first.

Takeaway. Knowing variables, data types, and memory makes classification click instantly.