📚 Year 13 Edexcel Computer Science: Key Terminology Quick Guide | Year 13 Edexcel 计算机：核心术语速记指南
Mastering the terminology is crucial for Year 13 Edexcel Computer Science. This guide provides memory-friendly explanations and vivid analogies to help you quickly recall key terms across the syllabus.
掌握术语对于 Year 13 Edexcel 计算机科学至关重要。本指南提供便于记忆的解释和生动的类比，帮助你快速回顾考纲中的关键术语。
1. Abstract Data Types & Data Structures | 抽象数据类型与数据结构
Stack: An abstract data type that follows Last In First Out (LIFO) ordering. The main operations are push (add to top), pop (remove from top) and peek (examine top). Think of a stack of plates: you can only take the top plate.
栈：一种遵循后进先出（LIFO）顺序的抽象数据类型。主要操作有 push（压入栈顶）、pop（弹出栈顶）和 peek（查看栈顶）。想象一叠盘子：只能拿最上面的盘子。
Queue: An ADT following First In First Out (FIFO). Items join at the rear and leave from the front. Visualise a checkout line — first come, first served.
队列：遵循先进先出（FIFO）的抽象数据类型。元素从队尾加入，从队首离开。联想超市结账排队：先到先服务。
Linked List: A dynamic data structure consisting of nodes, each containing data and a pointer to the next node. Unlike arrays, elements are not stored contiguously in memory. Think of a treasure hunt where each clue points to the next location.
链表：由节点组成的动态数据结构，每个节点包含数据和指向下一个节点的指针。与数组不同，元素不连续存储在内存中。想象寻宝游戏，每个线索指向下一个地点。
2. Algorithm Complexity & Big O Notation | 算法复杂度与大O表示法
Time Complexity: A measure of how the run time of an algorithm grows with input size n. Usually expressed using Big O notation O(f(n)), focusing on the dominant term.
时间复杂度：衡量算法运行时间随输入规模 n 增长如何变化的指标。通常用大O符号 O(f(n)) 表示，关注最高阶项。
Common growth orders: O(1) constant (hashing), O(log n) logarithmic (binary search), O(n) linear (linear search), O(n log n) linearithmic (merge sort), O(n²) quadratic (bubble sort).
常见增长阶：O(1) 常数阶（哈希），O(log n) 对数阶（二分查找），O(n) 线性阶（线性查找），O(n log n) 线性对数阶（归并排序），O(n²) 平方阶（冒泡排序）。
Big O, Theta, Omega: Big O gives worst-case upper bound (O), Omega gives best-case lower bound (Ω), Theta gives tight bound (θ) when O and Ω coincide. Memory aid: O for 'Oh, it's at most', Omega looking like a bottom, Theta is tight.
大O、θ、Ω：大O表示最坏情况的上界(O)，Ω表示最好情况的下界，θ表示紧界（当O和Ω相等）。记忆技巧：O像“哦，最多就这么慢”；Ω像一个底，表示最低；θ表示紧密贴合。
3. Graph Traversal and Pathfinding | 图遍历与寻路
BFS (Breadth-First Search): Traverses a graph level by level using a queue. Guarantees the shortest path in unweighted graphs. Visualize ripples spreading from a stone dropped in water.
广度优先搜索：使用队列逐层遍历图。在无权图中保证找到最短路径。想象石头落水后涟漪扩散。
DFS (Depth-First Search): Explores as far as possible along a branch before backtracking, using a stack (or recursion). Useful for maze generation. Like following a single thread in a labyrinth until you hit a dead end.
深度优先搜索：尽可能沿一条分支深入探索，无法前进时回溯，使用栈（或递归）。常用于迷宫生成。如同在迷宫中沿一条线走到死胡同再折返。
Dijkstra's Algorithm: Finds shortest paths from a start node in a weighted graph with non‑negative edges. Uses a priority queue. A* algorithm improves it with a heuristic (estimated distance to goal).
迪杰斯特拉算法：在非负权重的加权图中寻找从起点出发的最短路径。使用优先级队列。A*算法利用启发式函数（到目标的估计距离）对其进行改进。
4. Recursion and Divide & Conquer | 递归与分治法
Recursion: A function calling itself with a smaller subproblem. Must have base case to stop. Think of Russian nesting dolls: you open one doll to find a smaller one inside, until the smallest is reached.
递归：函数调用自身解决规模更小的子问题。必须有基本情况以终止。联想俄罗斯套娃：打开一个娃娃，里面有个更小的，直到最小的那个。
Merge Sort: A divide-and-conquer algorithm splitting the list into halves, recursively sorting them, then merging. Complexity O(n log n). Useful for large datasets.
归并排序：一种分治算法，将列表不断二分，递归排序子列表，然后合并。复杂度O(n log n)。适合大数据集。
Quick Sort: Chooses a pivot, partitions the array into elements less than and greater than pivot, recursively sorts partitions. Average O(n log n), but worst-case O(n²) with poor pivot choice.
快速排序：选取枢轴，将数组划分为小于和大于枢轴的两部分，递归排序。平均O(n log n)，但枢轴选择不当会导致最坏O(n²)。
5. Computational Theory: Turing Machines & Computability | 计算理论：图灵机与可计算性
Turing Machine: A theoretical model of computation consisting of a tape, head, state register and a finite set of instructions. It can simulate any algorithm. Basis of computability theory.
图灵机：包含纸带、读写头、状态寄存器和有限指令集的理论计算模型。能模拟任何算法。是可计算性理论的基础。
Halting Problem: It is impossible to write a program that can determine, for any arbitrary program and input, whether that program will halt or run forever. This proves limits of computation.
停机问题：不可能编写一个程序，对于任意程序和输入，判定该程序是否会终止。这证明了计算的局限性。
n polynomial time. NP problems can be verified in polynomial time; some NP problems are NP‑complete. Whether P = NP is a major open question.
P与NP问题：P类问题可在多项式时间内求解。NP类问题可在多项式时间内验证解；有些NP问题是NP完全的。P是否等于NP是一个重要的开放问题。
6. Programming Paradigms: OOP and Functional | 编程范式：面向对象与函数式
Object-Oriented Concepts: Encapsulation bundles data and methods; inheritance allows child class to reuse parent; polymorphism lets objects of different types respond to the same method call.
面向对象概念：封装将数据和方法绑定；继承允许子类重用父类；多态使不同类型的对象对同一方法调用做出不同响应。
Functional Programming: Emphasises pure functions, immutability, first-class functions, and higher-order functions (map, filter, fold). Avoids side effects. Think of a spreadsheet where formulas always produce the same output from given inputs.
函数式编程：强调纯函数、不可变性、一等函数和高阶函数（map, filter, fold）。避免副作用。想象电子表格：给定输入，公式总是产生相同输出。
Association vs Aggregation vs Composition: Association is a 'uses‑a' relationship; aggregation is a 'has‑a' weak ownership (child can exist independently); composition is a 'part‑of' strong ownership (child lifecycle dependent).
关联vs聚合vs组合：关联是“使用”关系；聚合是弱拥有“拥有”关系（子对象可独立存在）；组合是强拥有“部分”关系（子对象生命周期依赖于整体）。
7. Databases & SQL | 数据库与SQL
Normalisation: Process of organising data to reduce redundancy. 1NF: atomic values, no repeating groups. 2NF: meet 1NF and non‑key attributes fully depend on primary key. 3NF: meet 2NF and no transitive dependency.
规范化：减少数据冗余的组织过程。1NF：原子值，无重复组。2NF：满足1NF且所有非主属性完全依赖于主键。3NF：满足2NF且无传递依赖。
SQL JOINs: INNER JOIN returns matching rows from both tables; LEFT JOIN returns all rows from left table and matched rows; RIGHT JOIN returns all from right; FULL JOIN returns all when match exists.
SQL连接：内连接返回两表匹配行；左连接返回左表所有行及匹配行；右连接返回右表所有行及匹配；全连接返回任意匹配行。
Primary and Foreign Keys: Primary key uniquely identifies each record. Foreign key establishes a link to a primary key in another table, enforcing referential integrity.
主键与外键：主键唯一标识每条记录。外键建立与另一表主键的链接，强制引用完整性。
8. Networking & Protocols | 网络与协议
TCP/IP Stack Layers: Application (HTTP, DNS), Transport (TCP, UDP), Internet (IP), Network Access. Data passes down layers on sending, up on receiving. Memory trick: 'All Teachers Insist on Naps'.
TCP/IP协议栈分层：应用层(HTTP, DNS)、传输层(TCP, UDP)、网络层(IP)、网络接入层。发送时数据逐层向下，接收时向上。记忆口诀：“All Tigers Play Noisily”等。
Packet Switching: Data is split into packets, each containing source/destination address and sequence number. Routers forward packets independently; reassembled at destination. Like sending a book page by page via different postal routes.
分组
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