📚 Case Study Practical Exercises | 案例分析实战演练
Case studies form a core part of the Eduqas GCSE Computer Science assessment, especially in Component 2: Computational Thinking and Programming. They require you to read a scenario, analyse requirements, design algorithms, and evaluate solutions in a structured way. This practical guide will walk you through each stage of tackling a case study, with hands-on examples and revision-ready techniques to help you achieve top marks.
案例分析是 Eduqas GCSE 计算机科学考核的核心部分，尤其是在组件二《计算思维与编程》中。它要求你阅读场景，分析需求，设计算法并以结构化方式评估解决方案。本实战指南将带你走完案例分析的每一个环节，配合可上手的示例和备考技巧，帮助你拿下高分。
1. Understanding the Case Study | 理解案例研究
Begin by reading the given scenario at least twice. Underline or highlight the command words – verbs such as 'calculate', 'design', 'explain', 'evaluate' – because they tell you exactly what the mark scheme expects. Also circle the key nouns, like 'bus timetable', 'user input', 'touch screen', 'real-time updates'. This initial scan ensures you do not miss vital functional details.
首先，把给出的场景至少读两遍。用下划线或高亮标出指令词——比如 'calculate'、'design'、'explain'、'evaluate' 这样的动词——因为它们直接告诉了你评分方案的要求。同时圈出关键名词，如 'bus timetable'、'user input'、'touch screen'、'real-time updates'。这第一遍浏览能确保你不会遗漏重要的功能性细节。
Next, summarise the problem in one sentence: 'The system must allow a passenger to find the next bus from a stop and display the arrival time on a screen.' This simple statement keeps you focused during decomposition and design. Always refer back to it if you feel the solution is drifting.
接着，用一句话概括问题：'系统必须让乘客从公交站查询下一班车，并在屏幕上显示到达时间。' 这个简单陈述能让你在分解和设计过程中保持专注。如果你觉得方案开始跑偏，就回来看看这句话。
2. Identifying Functional and Non-Functional Requirements | 识别功能性与非功能性需求
Functional requirements describe what the system must do. In a bus timetable app, examples include: accept a stop number, retrieve timetable data, calculate the next departure, and display it. Write these in a bullet list as user stories or simple 'shall' statements, e.g., 'The app shall accept a 4-digit stop code.'
功能性需求描述了系统必须做什么。以公交时刻表应用为例：接受一个站台编号，调取时刻表数据，计算下一班发车时间，并显示出来。把这些写成要点列表，用用户故事或简单的“应……”陈述，比如 'The app shall accept a 4-digit stop code.'
Non-functional requirements specify how the system performs. Think about speed ('response time under 2 seconds'), usability ('accessible to visually impaired users via audio output'), reliability, and security. Eduqas examiners often reward identification of these 'quality' aspects, even if the scenario does not state them explicitly.
非功能性需求规定了系统的性能表现。考虑速度（'响应时间低于2秒'）、可用性（'通过音频输出对视障用户可访问'）、可靠性和安全性。即使情景中没有明确说明，Eduqas 的考官通常也会奖励对这些“质量”要素的识别。
3. Decomposition and Abstraction | 问题分解与抽象
Decomposition breaks the problem into smaller, manageable sub-problems. For the bus app, you could split it into: input handling, timetable storage, matching the current time to the next bus, and output generation. Each sub-problem can then be solved independently, which mirrors the modular approach expected in good programming.
问题分解将问题拆分成更小、更易管理的子问题。对于公交应用，可以拆分成：输入处理、时刻表存储、当前时间与下一班车的匹配，以及输出生成。每个子问题都可以独立解决，这正好体现了优秀编程所期望的模块化思想。
Abstraction is about hiding unnecessary complexity. A passenger does not need to see the raw database; a simple 'next bus in 5 min' message is sufficient. When modelling, you might represent the timetable as a 2D array of times and route IDs, ignoring GPS coordinates or driver names. Knowing what to leave out is just as important as what to include.
抽象就是隐藏不必要的复杂性。乘客不需要看到原始数据库；一条简单的 “下一班车 5 分钟后到达” 的信息就够了。建模时，你可以用时间与线路 ID 构成的二维数组来表示时刻表，忽略 GPS 坐标或司机姓名。知道该舍去什么与知道该引入什么同样重要。
4. Creating an IPO Chart | 创建输入-处理-输出表
An IPO (Input-Process-Output) chart captures the data flow at a high level. It is a simple, examiner-friendly way to show you understand the system boundaries before coding. For the bus timetable case, a basic IPO might look like this:
IPO （输入-处理-输出）表能在高层面上捕捉数据流。这是一种简单又讨考官喜欢的方法，能在编码前体现你对系统边界的理解。对于公交时刻表案例，一个基本的 IPO 表可能长这样：
| Input | Process | Output |
|---|---|---|
| Stop code (string) Current time (system clock) | Search timetable file for matching stop Compare current time with departure times Select first time greater than current time | Next bus route number Departure time (hh:mm) Wait time in minutes |
The chart can be refined further by adding data stores (e.g., timetable database) or feedback loops, but a clear, three-column IPO is often sufficient for GCSE tasks.
还可以通过添加数据存储（比如时刻表数据库）或反馈环路来细化，但对 GCSE 任务来说，清晰的三列 IPO 表通常就足够了。
5. Designing an Algorithm with Pseudocode | 用伪代码设计算法
Eduqas does not prescribe a single pseudocode syntax; you may use a style similar to OCR or AQA, as long as it is clear and consistent. The key constructs—assignment, selection, iteration—must be unambiguous. Below is a pseudocode solution for finding the next bus:
Eduqas 没有规定单一的伪代码语法；你可以使用类似 OCR 或 AQA 的风格，只要清晰、一致即可。赋值、选择、迭代等关键结构必须无歧义。以下是查找下一班车的伪代码解法：
INPUT stopCode currentHour ← SYSTEM_HOUR currentMinute ← SYSTEM_MINUTE nextBusTime ← "No bus today" minGap ← INFINITY OPEN timetable AS file WHILE NOT end of file DO READ record IF record.stop = stopCode THEN recordHour ← record.hour recordMinute ← record.minute gap ← (recordHour×60 + recordMinute) − (currentHour×60 + currentMinute) IF gap ≥ 0 AND gap < minGap THEN minGap ← gap nextBusTime ← record.route & " at " & recordHour & ":" & recordMinute ENDIF ENDIF ENDWHILE OUTPUT nextBusTime, minGap, "minutes wait"
The pseudocode uses a WHILE loop to scan each record, selection to check the stop code, and arithmetic to calculate the time gap. It assumes times are stored as 24-hour integers. Notice how variables are explicitly initialised, which helps trace tables and verification.
这段伪代码用 WHILE 循环逐条扫描记录，用选择结构检查站台代码，再通过算术计算时间差。它假设时间以 24 小时制整数的形式存储。请注意变量被显式初始化，这对后续的跟踪表和验证很有帮助。
6. Flowchart Notation and Drawing | 流程图符号与绘制
Flowcharts give a visual representation of the algorithm, which can often reveal logic flaws invisible in text. The Eduqas specification expects you to recognise standard symbols: an oval for Start/End, a parallelogram for Input/Output, a rectangle for Process, and a diamond for Decision. Arrows show the flow of control.
流程图提供了算法的可视化表示，往往能揭示文字中看不见的逻辑缺陷。Eduqas 考纲希望你识别标准符号：椭圆表示开始/结束，平行四边形表示输入/输出，矩形表示处理过程，菱形表示判断。箭头指示控制流。
For the bus timetable algorithm, the flowchart would begin with a 'Start' oval, followed by an input symbol for the stop code and a process box to load the system time. Then a decision diamond checks 'More records?'. The 'Yes' branch leads to another diamond to validate the stop match, and subsequent processes update nextBusTime. The loop continues until the file ends. Finally, the output symbol displays the result, and the flow reaches 'End'.
对于公交时刻表算法，流程图以一个 'Start' 椭圆开始，接着是一个用于输入站台代码的输入符号和一个加载系统时间的处理框。然后一个判断菱形检查 '还有更多记录吗？'。'是' 分支通向另一个菱形来验证站台匹配，后续处理框更新 nextBusTime。循环持续到文件结束。最后，输出符号显示结果，流程到达 'End'。
While you do not always have to draw the full chart in an exam, being able to sketch the main decision paths quickly demonstrates strong algorithmic thinking and earns marks for design.
虽然在考试中你不一定要画出完整流程图，但能快速勾画出主要决策路径能展现扎实的算法思维，并为设计环节赢得分数。
7. Building a Trace Table | 构建跟踪表
A trace table is a systematic way to test an algorithm manually. You list all variables in columns and step through the pseudocode line by line, updating values. This technique is essential for identifying logical errors and is regularly examined.
跟踪表是一种通过手动模拟来测试算法的系统方法。你把所有变量列入各列，然后逐行步进伪代码，更新数值。这种技术对于发现逻辑错误至关重要，也是常见的考核内容。
Take the above pseudocode with a scenario where current time is 10:05 and the timetable contains stops with times 09:45, 10:10, and 10:20 for the requested stop. A partial trace table would appear as:
以上述伪代码为例，假设当前时间是 10:05，而时刻表中请求站台包含 09:45、10:10 和 10:20 的记录。部分跟踪表如下：
| Line | recordHour | recordMinute | gap | minGap | nextBusTime |
|---|---|---|---|---|---|
| Initial | – | – | – | INF | 'No bus' |
| Read 09:45 | 9 | 45 | -20 | INF | 'No bus' |
| Read 10:10 | 10 | 10 | 5 | 5 | 'R2 at 10:10' |
| Read 10:20 | 10 | 20 | 15 | 5 | 'R2 at 10:10' |
The negative gap for 09:45 is ignored (gap < 0 not satisfied), and the smallest non-negative gap correctly identifies the 10:10 bus. Trace tables like this prove your algorithm works before any code is written.
09:45 的负时间差被忽略（不满足 gap ≥ 0），而最小的非负时间差正确识别出了 10:10 的班次。像这样的跟踪表能在编写任何代码之前就证明你的算法有效。
8. Developing a Test Plan | 制定测试计划
A thorough test plan covers normal, boundary, and erroneous data. For the bus app, normal data might be a valid stop code during service hours, expecting the correct next departure. Boundary cases include the first and last bus of the day, as well as the exact current time coinciding with a departure. Erroneous data would be an invalid stop code or a corrupted timetable file.
一份完整的测试计划包含正常数据、边界数据和错误数据。对于公交应用，正常数据可能是在服务时段内的有效站台代码，预期输出正确的下一班发车。边界情形包括当天的首班和末班车，以及当前时间恰好与某一发车时间重合的情况。错误数据则可以是无效站台代码或损坏的时刻表文件。
Present your test plan as a table with columns: Test ID, Input, Expected Output, Purpose, and Actual Result (if you later run the program). This structured approach is exactly what examiners want to see when they ask for a 'test strategy' or 'test plan'. Below is a simplified example:
用表格来呈现你的测试计划，包含列：测试编号、输入、预期输出、目的以及实际结果（如果你后续运行了程序）。考官问到“测试策略”或“测试计划”时，想看到的就是这种结构化方法。以下是一个简化示例：
| ID | Input | Expected Output | Type |
|---|---|---|---|
| T1 | Stop 'ST04', time 10:05 | 'Route 2 at 10:10, 5 min wait' | Normal |
| T2 | Stop 'ST04', time 23:50 (last bus 23:45) | 'No bus today' | Boundary |
| T3 | Stop 'FAKE' | 'Stop not found' | Erroneous |
Remember to justify why you chose each test case—briefly note the condition it covers, such as 'tests handling of stop code not in file'. This elevates your answer from a mere table to an analytical reasoning piece.
记住要说明你为什么选择每个测试用例——简要说明它覆盖的条件，比如 'tests handling of stop code not in file'。这能让你的答案从一个单纯的表格提升为带有分析推理的解答。
9. Considering Legal, Ethical, and Environmental Issues | 考虑法律、伦理与环境问题
Eduqas case studies often include a 'wider issues' requirement. Legally, any system that stores personal data (e.g., a passenger's stop history) must comply with GDPR: data must be processed lawfully, kept secure, and not kept longer than necessary. You should state that anonymisation and encryption are key technical measures.
Eduqas 的案例分析经常会包含“更广泛问题”的要求。法律上，任何存储个人数据（比如乘客的站台历史记录）的系统都必须遵守 GDPR：数据必须合法处理、安全保管，并且保留时间不超过必要期限。你应当指出匿名化和加密是关键技术措施。
Ethically, consider accessibility—can a person with visual impairment use the app? Does the system provide equal service regardless of language or disability? Also, does the timetable data fairly represent all communities served by the bus network? These subtle points show critical thinking.
伦理上，要考虑可访问性——视障人士能使用这个应用吗？系统是否不论语言或残疾情况都提供平等服务？此外，时刻表数据是否公平地反映了公交网络所服务的所有社区？这些细致的点能展现你的批判性思维。
Environmentally, digital systems still consume energy. Optimising algorithms to reduce server load, using dark mode on displays to save battery, and encouraging digital timetables over printed ones can all be mentioned. While these may seem minor, examiners appreciate awareness of sustainability.
环境方面，数字系统依然消耗能源。可以提及优化算法以减少服务器负载、在显示器上使用深色模式以节省电量、鼓励使用数字时刻表替代纸质打印。这些看起来虽小，但考官欣赏你对可持续性的关注。
10. Evaluating the Solution | 评估解决方案
Evaluation goes beyond 'it works'. Consider efficiency: does the algorithm scan every record even after finding the next bus? If so, it could be improved with a 'break' after the first valid match. Discuss robustness—what happens if the timetable file is empty or time data is in an unexpected format?
评估不仅仅是“它运行正常”。要考虑效率：算法在找到下一班车后是否还在继续扫描每一条记录？如果是，可以加入一个找到第一个有效匹配后的“跳出”来改进。讨论健壮性——如果时刻表文件为空，或时间数据的格式出乎意料，会发生什么？
Compare your solution with possible alternatives. A binary search on a sorted timetable could be faster, but might require more memory. Describe trade-offs clearly. Also, tie back to the original requirements: does the solution fully meet them? If any requirement is partially met, suggest future enhancements, such as integrating real-time GPS tracking for live delays.
将你的方案与可能的替代方案进行比较。对排好序的时刻表使用二分查找可能更快，但可能需要更多内存。清晰地描述这种权衡。同时，回头对照原始需求：方案是否完全满足需求？如果有需求只是部分满足，就提出未来的增强方案，比如整合实时 GPS 追踪以应对延误。
This reflective commentary often appears in the higher-mark band. Use phrases like 'a limitation of my algorithm is …' and 'this could be mitigated by …' to demonstrate a mature, evaluative mindset.
这类反思性评述通常会出现在高分区间。使用诸如“我的算法的一个局限是……”以及“这可以通过……来缓解”这样的句式，展示出一种成熟的评估思维。
11. Common Pitfalls and Tips | 常见陷阱与技巧
Pitfall 1: Overlooking explicit command words. If the question says 'design', don't just explain—you must provide pseudocode or a flowchart. If it says 'evaluate', you must give balanced pros and cons, not just a description. Keep a checklist of Eduqas command words and their meanings during revision.
陷阱一：忽略明确的指令词。如果题目说 'design'，你不要只是解释，必须给出伪代码或流程图。如果题目说 'evaluate'，你必须给出平衡的优缺点，而不仅仅是描述。复习时请备好一份 Eduqas 指令词及其含义的清单。
Pitfall 2: Poor variable initialisation. In trace tables and pseudocode, always set initial values for counters, accumulators, and flags. An uninitialised variable can lead to unpredictable results and lost marks. Write a comment or explicit assignment at the top of your algorithm.
陷阱二：变量初始化不当。在跟踪表和伪代码中，一定要为计数器、累加器和标志变量设置初始值。未初始化的变量可能导致不可预测的结果并丢分。在你的算法顶部写一段注释或显式赋值。
Pitfall 3: Ignoring non-functional requirements. Many candidates focus only on features, forgetting reliability, usability, and performance. Even a brief mention of 'the system shall respond within 3 seconds' or 'the interface shall use large, high-contrast text' can gain extra marks.
陷阱三：忽视非功能性需求。很多考生只关注功能，忘记了可靠性、可用性和性能。即使只是简单提一句 'the system shall respond within 3 seconds' 或 'the interface shall use large, high-contrast text' 也能多拿分。
Tip: Practise with past case studies and create your own variations. Time yourself: in Component 2 you will have roughly 20–25 minutes for the case study section. Being fluent in constructing IPO charts, pseudocode, and trace tables will save precious exam time.
技巧：用往年的案例研究进行练习，并自己创造变式。给自己计时：在组件二考试中，案例研究部分大约只有 20 到 25 分钟。能够熟练构建 IPO 表、伪代码和跟踪表，会为你节省宝贵的考试时间。
12. Practice Case Study: Bus Timetable App | 实战案例：公交时刻表应用
Here is a condensed case study to apply everything you have learned. Imagine a brief: 'A local council wants a digital display at bus stops. Passengers enter a 5-digit stop code on a touch keypad. The system looks up the next three bus departures from an internal schedule file and shows them with route numbers and wait times. It must be usable by elderly passengers and work even when the network is slow.'
以下是一个浓缩案例，用于应用你学到的所有内容。假设题干如下：“本地市议会希望在公交站安装数字显示屏。乘客在触摸键盘上输入一个 5 位站台代码。系统从内部时刻表文件中查找接下来的三趟公交车
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