What is a data structure?

An organised collection of related data items, stored together in a defined arrangement so that the data can be accessed and manipulated efficiently. The structure defines both how the items are held in memory and the operations that may be performed on them.

What is the difference between an abstract data type and a data structure?

An abstract data type is a logical description of what data is held and which operations may be performed on it, with no statement of how it is implemented. A data structure is the concrete implementation that actually stores the data in memory. For example, a stack is an abstract data type with push and pop operations; it may be implemented as a data structure using an array plus a top pointer, or using a linked list.

Give four everyday contexts that behave like a data structure you have studied.

A queue at a supermarket till behaves like a queue (first in, first out). A stack of plates behaves like a stack (last in, first out). A telephone contacts list that finds a number from a name behaves like a dictionary (a value looked up by its key). A road map with towns and roads behaves like a weighted graph.

Why do programmers choose a particular data structure for a problem?

Because the structure determines how efficiently the operations the program needs most can be carried out. Choosing a structure whose natural operations match the problem gives faster code and simpler logic — for example a queue for jobs waiting for a printer, a stack for undo history, a graph for a road network, a hash table for fast lookup by key.

Describe a one-dimensional array.

A run of elements that all share one data type, stored under a single identifier and reached by an index. For example an array of ten integers might be indexed 0 to 9, and element 3 is accessed as a[3]. One-dimensional arrays are a natural fit for holding a vector.

What is a two-dimensional array a useful way of representing?

A matrix — or more generally any table of values with rows and columns, such as a grid, a game board, or an adjacency matrix for a graph. Each element is accessed by two integer indices, one for the row and one for the column.

AQA AS-Level Computer Science 7517

Fundamentals of Programming

Topic overview Data types Programming concepts and program structure Arithmetic operations Relational Operations, Constants and Variables Boolean operations String-handling operations Random numbers and exception handling Subroutines, parameters and return values Variable scope and stack frames Programming paradigms and the procedural approach

Fundamentals of Data Structures

Topic overview Data Structures and Abstract Data Types

Theory of Computation

Topic overview Logic Problems and Algorithm Constructs Pseudo-Code, Hand-Tracing and Program Correctness Representational Abstraction, Generalisation and Information Hiding Procedural and Functional Abstraction Data Abstraction and Problem Reduction Decomposition and Composition Automation and Finite State Machines

Fundamentals of Data Representation

Topic overview Number systems and the sets of numbers Number bases: decimal, binary and hexadecimal Bits, bytes and units of information Unsigned binary and binary arithmetic Signed binary using two's complement Fixed point and floating point representation Character coding systems Error checking and correction Bit patterns, analogue and digital Bitmapped graphics Digital representation of sound MIDI and Data Compression Encryption

Fundamentals of Computer Systems

Topic overview Hardware, Software and Its Classification System Software and the Operating System Translators and the Role of the Operating System Classification of programming languages Types of program translator Logic Gates and Their Truth Tables Boolean algebra

Fundamentals of Computer Organisation and Architecture

Topic overview Internal components, buses and von Neumann and Harvard architectures The Stored Program Concept and the Processor The Fetch-Execute cycle The processor instruction set Addressing modes Machine-Code Operations Shifts, Halting and Assembly Language Programs Factors affecting processor performance Input and output devices Secondary storage devices

Fundamentals of Communication and Networking

Topic overview Communication methods Communication basics Network Topology and Types of Networking Wireless networking

Consequences of Uses of Computing

Topic overview The Four Kinds of Issue in Computing Legislation, Ethical Dilemmas and Case Studies

Systematic Approach to Problem Solving

Topic overview Analysis, Design and Implementation Testing and Evaluation

Fundamentals of Data Structures

1 subtopics
25 things to know
Paper 1

What Fundamentals of Data Structures covers

Arrays, records and files, then the abstract data types — stacks, queues, graphs, trees, hash tables and dictionaries — with the operations and traces each is examined through. Examined on Paper 1.

Where it is assessed

Paper 1

The on-screen programming exam, 2 hours 30 minutes and 40% of the A-level.

Check the AQA specification ↗

The 1 subtopics

Each one has its own page. AQA AS Computer Science students sit this topic in the first year.

Data Structures and Abstract Data TypesRecall questions on what a data structure is, how it differs from an abstract data type and why a particular structure is chosen.Open →

What is a priority queue, and what decides the order items leave it?

Evaluation

Compare a linear queue with a circular queue.

Take Fundamentals of Data Structures further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

Stack vs Queue
Stack: a last-in-first-out collection accessed at one end. Queue: a first-in-first-out collection entered and left at opposite ends.
Static structure vs Dynamic structure
Static structure: a collection whose allocated size stays fixed during execution. Dynamic structure: a collection whose allocated size can change during execution.
Text file vs Binary file
Text file: stored characters interpreted through a character encoding. Binary file: stored bit patterns interpreted through an agreed record format.

Questions from this topic

Each one with the model answer underneath.

1
What is a data structure?
Model answer
An organised collection of related data items, stored together in a defined arrangement so that the data can be accessed and manipulated efficiently. The structure defines both how the items are held in memory and the operations that may be performed on them.
2
What is the difference between an abstract data type and a data structure?
Model answer
An abstract data type is a logical description of what data is held and which operations may be performed on it, with no statement of how it is implemented. A data structure is the concrete implementation that actually stores the data in memory. For example, a stack is an abstract data type with push and pop operations; it may be implemented as a data structure using an array plus a top pointer, or using a linked list.
3
Give four everyday contexts that behave like a data structure you have studied.
Model answer
A queue at a supermarket till behaves like a queue (first in, first out). A stack of plates behaves like a stack (last in, first out). A telephone contacts list that finds a number from a name behaves like a dictionary (a value looked up by its key). A road map with towns and roads behaves like a weighted graph.
4
Why do programmers choose a particular data structure for a problem?
Model answer
Because the structure determines how efficiently the operations the program needs most can be carried out. Choosing a structure whose natural operations match the problem gives faster code and simpler logic — for example a queue for jobs waiting for a printer, a stack for undo history, a graph for a road network, a hash table for fast lookup by key.
5
Describe a one-dimensional array.
Model answer
A run of elements that all share one data type, stored under a single identifier and reached by an index. For example an array of ten integers might be indexed 0 to 9, and element 3 is accessed as a[3]. One-dimensional arrays are a natural fit for holding a vector.
6
What is a two-dimensional array a useful way of representing?
Model answer
A matrix — or more generally any table of values with rows and columns, such as a grid, a game board, or an adjacency matrix for a graph. Each element is accessed by two integer indices, one for the row and one for the column.

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Fundamentals of Programming

Fundamentals of Data Structures

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Fundamentals of Data Representation

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Fundamentals of Data Structures revision questions

Is Fundamentals of Data Structures examined at AS in AQA Computer Science?: Yes. It sits in Paper 1, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.
What does Fundamentals of Data Structures cover in AQA AS-Level Computer Science?: 1 subtopics: data structures and abstract data types. Each one has its own page with questions and model answers.
How is Fundamentals of Data Structures organised?: By the AQA 7517 specification, subtopic by subtopic, so it matches the order you are taught it in.

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