Chapter 50 — Final defense
Lesson map
Lesson 50 published. Map, example, EX148.
flowchart TD
N0["Learning outcomes"]
N1["50.1 Defense"]
N2["50.2 Questions"]
N3["50.3 Answers"]
N4["50.4 Reflection"]
N5["50.5 Next"]
N6["Preparing the defense"]
N7["Examiners' view"]
N0 --> N1 --> N2 --> N3 --> N4 --> N5 --> N6 --> N7
N7 --> EX["Worked example"]
EX --> Q["Exercise EX148"]
Logical drawing
flowchart LR
N0["Learning outcomes"]
N1["50.1 Defense"]
N2["50.2 Questions"]
N3["50.3 Answers"]
N4["50.4 Reflection"]
N5["50.5 Next"]
N6["Preparing the defense"]
N7["Examiners' view"]
N0 --> N1 --> N2 --> N3 --> N4 --> N5 --> N6 --> N7 --> Q["EX148"]
[Learning outcomes]
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[50.1 Defense]
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[50.2 Questions]
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[50.3 Answers]
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[50.4 Reflection]
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[50.5 Next]
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[Preparing the defense]
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[Examiners' view]
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[Worked example] --> [Exercise EX148]
Learning outcomes
You will (1) defend the thesis; (2) answer questions; (3) reflect on professional growth.
50.1 Defense
Mateo presents in thirty minutes and answers questions.
The presentation follows the thesis: problem, design, evidence, limits and lessons, with one slide for each. Mateo leaves more than half the time for questions, since that is where examiners test understanding. He brings a lab PC so he can show the out-of-service screen and a restore if asked. The rehearsals with classmates kept the talk within the time. He also prints the evidence index in case examiners want to check a claim during questions.
50.2 Questions
Examiners ask about privacy, accessibility and long-term costs.
The three topics reflect the project's main tensions. Privacy asks whether a design that monitors PCs also monitors people. Accessibility asks whether restrictions shut some patrons out. Long-term cost asks whether Fernhill can afford to keep the service running after the student leaves. The examiners also asked how firmware risk would be handled as models age. Mateo had prepared for all four during rehearsal, using questions his classmates and Marta had suggested, and kept a page reference ready for each.
50.3 Answers
Logs hold no content; accessibility tools were protected by audit-first; costs are mainly staff time, which fell.
Each answer points to evidence in the dossier: the list of logged fields approved by the data protection officer, the two audit weeks and the reader's addition, and the call study with the maintenance hours. Mateo keeps each answer short and offers the evidence rather than repeating it. When asked about firmware risk, he points to the residual risk register and the dashboard check for unapproved versions.
50.4 Reflection
Mateo learned that users shape security designs as much as threats do.
The clearest example was the accessibility reader: no threat analysis would have found that problem, but a week of audit data and a conversation with a librarian did. Patron needs also shaped the notices, the logoff warning and the saving guidance. Mateo now starts any design by asking who uses the system and what they need, before asking what could go wrong. Examiners asked for an example and he gave this one.
50.5 Next
Fernhill hires him part-time to maintain the service.
The part-time role continues the work under Marta's supervision while Mateo looks for a full-time post. He will run the annual review, the recovery trial and the maintenance tasks listed in the handover pack. Fernhill's decision is also a sign that the documentation works, since he is no longer the only person who can run the service. The course ends here, and the service carries on. Dr Novak remains a contact for advice.
Preparing the defense
Mateo rehearses with classmates, who ask hard questions. He prepares short answers with evidence for privacy, accessibility, costs, firmware risk and generalisation. He also prepares to admit limits: one organisation, older hardware and estimates mixed with measurements, clearly labelled.
Rehearsal helps him keep answers short.
Examiners' view
Examiners praise the link between requirements and evidence, the care for accessibility and privacy, and the honest labelling of estimates.
Course review
The course moved from mathematics and physics through programming, systems, security, requirements, design, implementation, verification, operations and research to a thesis and defense, all anchored in one public-service project.
Continuing
Mateo plans to follow vendor firmware notices, benchmark updates and research on endpoint integrity.
Boundaries
All testing used lab PCs and synthetic data or agreed trials outside opening hours.
Thanks
Mateo thanks everyone who helped.
Outcome
Mateo passes with minor corrections.
Final reflection
He notes that patient, careful testing mattered more than clever technology.
Advice to future students
Mateo advises future students to start conversations with users early, test assumptions with data and label estimates honestly.
Legacy
The service continues to run at Fernhill using the documented design and runbooks.
Feedback
Examiners recommend the thesis to future students.
Worked example
An examiner asks what he would change. He says he would involve librarians from the first week.
Synthetic case. Synthetic.
Errors and limits
Reflection should name specific changes.
Exercises
- EX148 — Examiner topics. Which topics did examiners raise? Rubric: 3 = privacy, accessibility, costs; 2 = two; 1 = one; 0 = none.
- EX149 — Accessibility answer. How was accessibility protected? Rubric: 3 = audit-first allowlist; 2 = partial; 1 = vague; 0 = none.
- EX150 — Change. What would Mateo change? Rubric: 3 = involve librarians from week one; 2 = partial; 1 = vague; 0 = none.
Synthesis
Defend with evidence and reflect specifically.
Continue studying — chapter 50 of 50
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