📚 Year 13 AQA Computer Science: Key Terms Memorisation Guide | AQA A-level计算机科学：词汇术语速记指南
For AQA A-Level Computer Science, a precise command of terminology can make the difference between a pass and a top grade. This article breaks down the essential vocabulary from Year 13 topics, pairing concise definitions with memory hooks and exam-ready explanations. Use it as a quick-reference glossary to reinforce your understanding and to ensure you always use terms correctly in written answers.
在AQA A-level计算机科学中，对术语的精确掌握往往决定了最终的成绩档位。本文梳理了Year 13核心主题中的关键词汇，为每个术语提供简明定义、记忆线索及适合答题的规范表述。你可以把它当作速查手册，巩固理解，并确保在笔答中始终准确使用专业术语。
1. Data Structures and ADTs | 数据结构与抽象数据类型
Abstract Data Types (ADTs) are logical descriptions of how data can be accessed and manipulated, without specifying the underlying implementation. They are defined by their behaviour (operations) rather than their concrete representation. Common ADTs at A-Level include stacks, queues, priority queues, lists, trees and graphs.
抽象数据类型（ADT）是对数据如何被访问与操作的逻辑描述，而不规定底层实现细节。它们由行为（操作）而非具体表示来定义。A-Level中常见的ADT包括栈、队列、优先队列、列表、树和图。
Stack: a Last-In-First-Out (LIFO) structure. The most recent item pushed onto the stack is the first to be popped off. Visualise a pile of plates: you can only take or place a plate from the top. Key operations: push(item), pop(), peek() or top(), and isEmpty(). Stacks are used for undo mechanisms, backtracking in recursion, and expression evaluation.
栈：后进先出（LIFO）结构。 最后推入栈的项最先被弹出。可以想象一摞盘子：你只能从顶部取放。主要操作：push(item)、pop()、peek()/top()以及isEmpty()。栈用于撤销机制、递归中的回溯以及表达式求值。
Queue: a First-In-First-Out (FIFO) structure. Items join at the rear and leave from the front, just like a real-world queue. Operations: enqueue(item), dequeue(), peek() and isEmpty(). Linear queues may suffer from wasted space; a circular queue reuses array slots by wrapping pointers around, improving efficiency. Queues underlie print spooling, breadth-first search and buffered I/O.
队列：先进先出（FIFO）结构。 元素从队尾加入，从队首离开，就像现实中的排队。操作：enqueue(item)、dequeue()、peek()和isEmpty()。线性队列可能出现空间浪费，而循环队列通过指针绕回重用数组槽位，效率更高。队列用于打印缓冲、广度优先搜索和I/O缓冲。
Linked List: a dynamic collection of nodes. Each node contains data and a pointer (or link) to the next node. In a doubly linked list, nodes also store a pointer to the previous node, enabling bidirectional traversal. No shifting is needed on insertion or deletion, unlike arrays, but access is sequential (O(n)). Variants include circular linked lists, useful for round-robin scheduling.
链表：动态的节点集合。 每个节点包含数据和指向下一个节点的指针（链接）。在双向链表中，节点还存储指向前一个节点的指针，支持双向遍历。插入或删除时无需移动元素（与数组不同），但访问是顺序的（O(n)）。变体包括循环链表，常用于轮转调度。
Binary Tree & Binary Search Tree (BST): hierarchical structures. A binary tree has at most two children per node. A BST enforces ordering: for any node, left subtree values are less, right subtree values are greater. This allows searching in O(log n) on average if the tree is balanced. Terminology: root, leaf, parent, child, subtree, depth. Traversals: pre-order, in-order, post-order.
二叉树与二叉搜索树（BST）：层次结构。 二叉树每个节点最多有两个子节点。BST强制有序：对任意节点，左子树值较小，右子树值较大。若树保持平衡，平均查找时间为O(log n)。术语：根、叶、父、子、子树、深度。遍历方式：前序、中序、后序。
Graph: a set of vertices (nodes) connected by edges. Edges can be directed or undirected, weighted or unweighted. Representation methods include adjacency matrix and adjacency list. A graph is used to model networks, social connections, road maps. A tree is a connected acyclic graph. Important graph algorithms: depth-first search (DFS), breadth-first search (BFS), Dijkstra’s shortest path.
图：由边连接的顶点（节点）集合。 边可以是有向/无向、带权/无权。表示方式包括邻接矩阵和邻接表。图用于建模网络、社交关系、道路地图。树是一种连通无环图。重要图算法：深度优先搜索（DFS）、广度优先搜索（BFS）、Dijkstra最短路径。
Hash Table: a key-value store with O(1) average lookup. A hash function maps a key to an index in an array. Collisions occur when two keys map to the same index; they are resolved by chaining (linked list at each bucket) or open addressing (probing for the next empty slot). Loading factor and a good hash function are critical to performance. Hash tables power dictionaries, caches, and associative arrays.
哈希表：平均O(1)查找的键值存储。 哈希函数将键映射为数组索引。当两个键映射到同一索引时发生冲突，通过链地址法（每个桶挂链表）或开放地址法（探测下一个空槽）解决。装载因子和良好的哈希函数对性能至关重要。哈希表用于字典、缓存和关联数组。
2. Object-Oriented Programming (OOP) | 面向对象编程
OOP models software as interacting objects rather than a sequence of procedures. It emphasises modularity, reusability and maintainability through four core principles: encapsulation, inheritance, polymorphism and abstraction. AQA questions frequently ask you to identify and explain these concepts in the context of a given scenario.
面向对象编程将软件建模为交互的对象而非线性过程。它通过四大核心原则——封装、继承、多态和抽象——来强调模块化、复用性和可维护性。AQA考题常要求你在给定情境中识别并解释这些概念。
Class and Object: A class is a blueprint or template defining attributes (fields) and behaviours (methods). An object is an instance of a class, with its own state. For example, a Car class describes properties like colour and speed; a specific red Toyota is an object of that class. Instantiation creates the object, typically via the new keyword and a constructor.
类与对象： 类是定义属性（字段）和行为（方法）的蓝图或模板。对象是类的实例，拥有自己的状态。例如，Car类描述颜色、速度等属性；一辆红色丰田则是该类的一个对象。实例化通过new关键字和构造函数创建对象。
Encapsulation: Bundling data with the methods that operate on that data, and restricting direct access to an object’s internal state. In practice, attributes are declared as private, and public getter and setter methods control access. This protects integrity and allows internal changes without affecting external code. Encapsulation is often summed up as “data hiding”.
封装： 将数据与操作数据的方法绑定，并限制对对象内部状态的直接访问。实践上，属性声明为私有，通过公有的getter和setter方法控制访问。这保护了完整性，并允许在不影响外部代码的情况下修改内部实现。封装常被概括为“数据隐藏”。
Inheritance: A mechanism where a child class (subclass) derives properties and behaviours from a parent class (superclass). The keyword extends is used in Java and similar syntax in other languages. This promotes code reuse and establishes an “is-a” relationship. For example, a Dog class inherits from Animal. Overriding allows a subclass to provide a specific implementation of a method defined in the superclass.
继承： 子类从父类（超类）派生属性和行为的机制。代码中常使用extends关键字（Java等）。这促进了代码复用，并建立“是”的关系。例如，Dog类继承自Animal。重写（Override）允许子类提供父类方法的具体实现。
Polymorphism: The ability of objects of different classes to respond to the same method call in their own way. Method overriding achieves runtime polymorphism; a parent reference can point to a child object, and the correct overridden method is called dynamically. Method overloading (compile-time polymorphism) allows multiple methods with the same name but different parameter lists. Polymorphism simplifies code and enhances flexibility.
多态： 不同类的对象能够以自己的方式响应同一方法调用。方法重写实现运行时多态：父类引用可指向子类对象，在运行时动态调用正确的重写方法。方法重载（编译时多态）允许同名方法但参数列表不同。多态简化代码并增强灵活性。
Abstraction: Hiding complex implementation details and exposing only essential features. In OOP, abstract classes cannot be instantiated; they define a common interface for subclasses. Interfaces (Java) or pure virtual classes (C++) take abstraction further by specifying only method signatures. The user of a class needs to know what it does, not how it does it.
抽象： 隐藏复杂实现细节，仅暴露必要功能。在OOP中，抽象类不能被实例化；它们为子类定义公共接口。接口（Java）或纯虚类（C++）进一步抽象，仅指定方法签名。类的使用者只需知道它做什么，无需知道如何做。
3. Computational Theory | 计算理论
The Hardware and Software topic stretches into theoretical models of computation. You need to understand Turing machines, the limits of computation, and the significance of complexity classes. This section also touches on the Universal Turing Machine and the Halting Problem, which underpin the notion of computability.
硬件与软件专题延伸到计算的理论模型。你需要理解图灵机、计算的极限以及复杂度类的重要性。本节还涉及通用图灵机和停机问题，它们是可计算性概念的基石。
Turing Machine (TM): An abstract computational model consisting of an infinite tape divided into cells, a read/write head that can move left or right, a finite set of states, and a transition function. Despite its simplicity, a TM can simulate any algorithm that a modern computer can execute—this is the Church-Turing thesis. A TM is deterministic if each state-symbol pair maps to at most one action.
图灵机： 一种抽象计算模型，包含划分为单元格的无限长纸带、可左右移动的读写头、有限状态集和转移函数。虽然简单，TM可以模拟现代计算机能执行的任何算法——这就是丘奇-图灵论题。若每个状态-符号对最多映射为一个动作，则TM是确定性的。
Universal Turing Machine (UTM): A TM that can simulate any other TM. The UTM’s input consists of a description of the target TM and that TM’s own input. This concept is the theoretical foundation of stored-program computers: a single machine can be reprogrammed to perform any computable task, just like loading different software.
通用图灵机（UTM）： 能模拟任何其他图灵机的TM。UTM的输入包含目标TM的描述和该TM自身的输入。这一概念是存储程序计算机的理论基础：一台机器可通过重编程执行任何可计算任务，正如加载不同软件。
Halting Problem: The decision problem of determining, given a description of a TM and an input, whether the machine will eventually halt or run forever. Alan Turing proved that no general algorithm can solve this problem for all possible TM-input pairs—it is undecidable. This demonstrates fundamental limits to computation.
停机问题： 给定一个TM的描述和输入，判定该机器最终会停机还是永远运行的决策问题。艾伦·图灵证明不存在通用算法能对所有可能的TM-输入对解决此问题——它是不可判定的。这证明了计算的固有局限。
Complexity Classes – P, NP, NP-complete, NP-hard: P is the set of decision problems solvable in polynomial time by a deterministic TM. NP can be solved in polynomial time by a non-deterministic TM, and a proposed solution can be verified in polynomial time. NP-complete problems are the hardest in NP; if any one of them can be solved in polynomial time, then P = NP. NP-hard problems are at least as hard as NP-complete, but not necessarily in NP. The TSP (decision version) is a classic NP-hard example.
复杂度类——P、NP、NP完全、NP难： P是可在确定性TM上多项式时间内解决的判定问题集合。NP可在非确定性TM上多项式时间解决，且其候选解可在多项式时间内验证。NP完全问题是NP中最难的一类；若其中任意一个能在多项式时间解决，则P=NP。NP难问题至少与NP完全一样难，但不一定属于NP。旅行商问题（判定版）是经典的NP难例子。
Big-O Notation for Expressing Time Complexity Growth: Big-O quantifies the worst-case growth of an algorithm’s resource usage relative to input size n. Examples: O(1) – constant, O(log n) – logarithmic (e.g., binary search), O(n) – linear, O(n log n) – linearithmic (e.g., merge sort), O(n²) – quadratic, O(2ⁿ) – exponential. Ignoring constants and lower-order terms makes comparisons meaningful.
用大O表示法描述时间复杂度增长： 大O量化了算法资源消耗相对输入规模n的最坏情况增长。例如：O(1)——常数，O(log n)——对数（如二分查找），O(n)——线性，O(n log n)——线性对数（如归并排序），O(n²)——平方，O(2ⁿ)——指数。忽略常数和低阶项使得比较有意义。
4. Networking Fundamentals | 网络基础
Computer networks underpin modern distributed applications. The AQA specification covers layered protocol models, the TCP/IP stack, common application-level protocols, and infrastructure services such as DNS and DHCP. Understanding encapsulation and the purpose of each layer is essential.
计算机网络支撑着现代分布式应用。AQA考纲涵盖分层协议模型、TCP/IP协议栈、常见应用层协议以及DNS、DHCP等基础服务。理解数据封装和每层的职责至关重要。
TCP/IP Stack: layers and their roles. The Application layer (HTTP, FTP, SMTP, DNS) provides services to user applications. The Transport layer (TCP, UDP) manages end-to-end communication, error recovery and flow control (TCP) or connectionless delivery (UDP). The Internet layer (IP) handles packet routing and logical addressing. The Network Access layer (Ethernet, Wi-Fi) deals with the physical transmission of frames. Data moves down the stack adding headers (encapsulation) and up the stack stripping them (de-encapsulation).
TCP/IP协议栈：分层与职责。 应用层（HTTP、FTP、SMTP、DNS）向用户程序提供服务。传输层（TCP、UDP）管理端到端通信，TCP提供错误恢复和流量控制，UDP提供无连接交付。网际层（IP）处理数据包路由和逻辑寻址。网络接入层（以太网、Wi-Fi）负责帧的物理传输。数据在栈中向下时添加首部（封装），向上时剥离首部（解封装）。
TCP vs UDP: TCP is connection-oriented, offers reliable, ordered delivery using sequence numbers, acknowledgements and retransmissions; it also implements flow and congestion control. UDP is connectionless, lightweight, with no guarantee of delivery or order—ideal for real-time audio/video streaming and DNS queries, where speed is prioritised over reliability. Think “TCP = careful delivery truck, UDP = fire-and-forget courier”.
TCP与UDP： TCP面向连接，通过序列号、确认和重传提供可靠、有序的交付；还实现流量控制和拥塞控制。UDP是无连接的，轻量级，不保证交付或顺序——适用于实时音视频流和DNS查询，这类应用优先速度而非可靠性。可记作”TCP = 谨慎的快递货车，UDP = 即发即走的信使”。
DNS (Domain Name System): Resolves human-readable domain names (e.g., aleveler.com) into IP addresses. It uses a hierarchical, distributed database with recursive and iterative resolution. DNS servers cache records to reduce lookup time. Record types include A (IPv4 address), AAAA (IPv6), CNAME (alias), MX (mail exchange). DNS runs over UDP (port 53) normally, but TCP fallback is used for large responses.
DNS（域名系统）： 将人类可读的域名（如aleveler.com）解析为IP地址。它采用层次化分布式数据库，支持递归和迭代解析。DNS服务器缓存记录以缩短查询时间。记录类型包括A（IPv4地址）、AAAA（IPv6）、CNAME（别名）、MX（邮件交换）。DNS通常运行在UDP端口53上，大响应时可回退至TCP。
DHCP (Dynamic Host Configuration Protocol): Automatically assigns IP configurations to devices on a network. The DORA process: Discover, Offer, Request, Acknowledgement. DHCP reduces manual configuration errors and reclaims addresses when devices leave. A DHCP server provides IP address, subnet mask, default gateway and DNS server addresses.
DHCP（动态主机配置协议）： 自动为网络上的设备分配IP配置。DORA流程：发现(Discover)、提供(Offer)、请求(Request)、确认(Acknowledgement)。DHCP减少了手动配置错误，并在设备离开时回收地址。DHCP服务器提供IP地址、子网掩码、默认网关和DNS服务器地址。
NAT and Port Forwarding: Network Address Translation modifies IP headers to allow multiple devices on a private LAN to share a single public IP. It conserves IPv4 addresses and adds a layer of security. Port forwarding maps a specific port on the public IP to a private internal IP and port, enabling external access to services such as a web server or game server hosted inside the LAN.
NAT与端口转发： 网络地址转换修改IP首部，使一个私有局域网内的多台设备共享单个公网IP。这节省了IPv4地址并增添了一层安全防护。端口转发将公网IP上的特定端口映射至内部私有IP和端口，从而允许外部访问局域网内托管的Web服务器或游戏服务器等服务。
5. Database Concepts & SQL | 数据库概念与SQL
Relational databases remain central to the AQA databases topic. You must understand normalization, the ACID properties of transactions, indexing, and SQL for both definition and manipulation. Being able to compare normal forms and justify design decisions is a typical exam skill.
关系数据库在AQA数据库课题中仍居核心地位。你需要理解规范化、事务的ACID特性、索引，以及用于定义和操控数据的SQL。能够比较范式并论证设计决策是典型的考试技能。
Relational Model & Keys: Data is stored in tables (relations) with rows (tuples) and columns (attributes). A primary key uniquely identifies each row. A foreign key links a column in one table to the primary key of another, enforcing referential integrity. Composite keys use multiple columns. Candidate keys are all columns that could serve as a primary key.
关系模型与键： 数据存储在表（关系）中，由行（元组）和列（属性）构成。主键唯一标识每一行。外键将一个表中的列与另一个表的主键关联，确保引用完整性。复合键使用多列。候选键是能作为主键的所有列。
Normalization (1NF, 2NF, 3NF): First Normal Form (1NF) eliminates repeating groups each column contains atomic values. Second Normal Form (2NF) removes partial dependencies (non-key attributes must depend on the whole primary key). Third Normal Form (3NF) eliminates transitive dependencies (non-key attributes must depend only on the primary key, not on another non-key column). A mnemonic: “Every non-key attribute must provide a fact about the key, the whole key, and nothing but the key.”
规范化（1NF、2NF、3NF）： 第一范式（1NF）消除重复组，每列含原子值。第二范式（2NF）消除部分依赖（非键属性必须依赖整个主键）。第三范式（3NF）消除传递依赖（非键属性必须只依赖于主键，而不能依赖另一个非键列）。一句助记：“每个非键属性必须给出关于键、整个键、且仅仅是键的事实。”
ACID (Atomicity, Consistency, Isolation, Durability): Guarantees of reliable transactions. Atomicity: a transaction is all-or-nothing. Consistency: a transaction brings the database from one valid state to another. Isolation: concurrent transactions do not interfere. Durability: once committed, a transaction’s changes persist even after a system failure. ACID is crucial for banking and booking systems.
ACID（原子性、一致性、隔离性、持久性）： 可靠事务的保证。原子性：事务要么全做，要么全不做。一致性：事务将数据库从一个有效状态带入另一个有效状态。隔离性：并发事务互不干扰。持久性：一旦提交，事务的更改在系统故障后依然存在。ACID对银行和预订系统至关重要。
Indexing: An index is a separate data structure (often a B-tree) that speeds up data retrieval on a column at the cost of extra storage and slower writes. Think of it as the index in the back of a textbook. A clustered index physically orders rows on disk by the indexed column (only one per table), whereas a non-clustered index stores a separate list of pointers. SQL: CREATE INDEX idx_name ON table(column);
索引： 索引是独立的数据结构（通常是B树），可加快对某列的检索，但会消耗额外存储并减慢写入。可以把它想象为教科书末尾的索引。聚集索引按索引列在磁盘上物理排列行（每表仅限一个），非聚集索引则存储单独的指针列表。SQL示例：
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