AFTER-CLASS · CHAPTER 10
Dependable Systems: a decision you can defend
Read the named source pages, check the five objectives, apply the concepts, then reassess your decision when new evidence appears. The total-time estimate includes preparation; report your actual time.
- Warm-up
- FIT → BOUND → ACT + EVIDENCE
- Commit Part A
- STRESS → REFIT
- Review and submit in LMS
1 · WARM-UP · 5 MINUTES · NOT GRADED
Start with one clear distinction.
An online timetable opens whenever requested, but sometimes displays yesterday’s timetable. Is availability alone enough to call it dependable?
Show / hide warm-up answer
No written warm-up response is required. Now transfer the reasoning to a different service in Part A.
Lecture guide and sentence stems
Use the lecture’s Chapter map to reconnect the concepts and Study & tools only when you need a source, rule or worksheet. You do not complete the 20-rule toolkit separately for this assignment. The required iSCARB disciplines are already built into the fields below: predict and bound the claim, label evidence honestly, name responsible roles, revise after STRESS, disclose AI assistance, read the rubric and finish with a bounded professional decision. Use Required source review to locate the assigned source slides.
FIT: The governing property is … because this service must …
BOUND: This decision remains acceptable only while …; reopen if …
ACT + EVIDENCE: My decision record says …; it is supported by …, checked by …
Chapter map · Relevant mechanism · 20-rule map · Practice card. Source and chapter-unit identifiers are not canonical rule numbers.
CURRENT EDITION · MASTERY V2
Required preparation and assessment scope
Read: Redundancy, diversity and shared causes: slides 26–31; Formal methods and their scope: slides 40–43.
Complete the five-objective preparation check after the assigned reading, before starting this task and before the next chapter discussion. Blackboard supplies the calendar deadline. All five chapter objectives, the classroom concepts and named reading are in assessment scope. Optional toolkit activities are enrichment unless assigned.
One assigned source application and one short transfer answer are included below, within the existing 4-point rubric. A reading click or a practice score is not proof of mastery.
Already started the previous edition? Resume or export your previous work using the same ID and browser. Previous drafts stay separate. Completed submissions do not need repeating unless the instructor requests it.
READ BEFORE ANSWERING
How your work is assessed · 4 points
| Criterion | Scoring |
|---|---|
| FIT · 1 point | 1: Relevant dependability property, a correctly linked mechanism, and a scenario-specific reason. The short transfer answer must correctly apply the second concept; FIT and transfer together earn this single point. Apply one named required source concept to the artifact and explain the connection. 0.75: The right dependability property and mechanism, but the scenario-specific reason is thin or the transfer answer applies the second concept only partly. 0.5: A property is named but not linked to the failure mechanism in the case, or the transfer answer is missing or incorrect. 0: No dependability property is applied, a property is chosen without justification, or the answer depends on invented facts. A generic “hold and test” statement does not satisfy this criterion. |
| BOUND · 1 point | 1: Observable condition and clear trigger to reopen, consistent with the plan. 0.75: A relevant boundary and trigger, but one is imprecise—for example, a trigger that cannot be observed as written. 0.5: The boundary is generic (“if problems occur”) or does not match the claim and the plan. 0: No boundary, or a boundary that contradicts the case facts. |
| ACT + EVIDENCE · 1 point | 1: Feasible immediate action with responsible role, plus inspectable evidence tied to its boundary; unknown or proposed evidence is labelled. 0.75: A feasible action and useful evidence, but one element is missing—for example, the responsible role, or whether the evidence is completed or proposed. 0.5: The action is vague or not feasible in the case, or the evidence cannot be inspected by someone else. 0: No action, or evidence that is invented or reported as completed when it is only proposed. |
| REFIT · 1 point | 1: Explains the effect on the original boundary, justifies RETAIN, REVISE or REPLACE, and supplies a coherent final plan. 0.75: The effect of the new evidence and the RETAIN / REVISE / REPLACE choice are justified, but the final record leaves one inconsistency with the new boundary. 0.5: A choice is stated but not justified from the new evidence, or the final record repeats Part A without addressing the change. 0: No REFIT, or a response that ignores or contradicts the new evidence. |
Any REFIT choice can earn full credit when justified; changing your answer earns no automatic credit. The instructor judges the reasoning, not language polish, length or box completion. The lecture’s L1–L4 maturity descriptions are a separate practice guide.
Lecture outcomes practised: explain dependability properties; build a bounded verdict with inspectable evidence; defend the verdict when a constraint changes. Comparing alternatives is practised when relevant; a full sociotechnical layer trace is not assessed in this first task.
How this assignment connects to the lecture
FIT: X01 / Rule 05 — properties and prediction. BOUND + EVIDENCE: Rules 07, 09 and 10 — decision card, failure conditions and risk. ACT: Rules 06 and 12 — engineering flow and accountable roles. REFIT: Rules 13 and 17 — breaking variables and changed constraints.
FIT → BOUND → ACT + EVIDENCE → STRESS → REFIT is the after-class record of the same decision-and-evidence approach used in the lecture.
Learning-outcome alignment
This task supports CLO 1 and 2 of the course specification (section B). It is course-written practice, not an official national readiness assessment or an approved item-weight mapping.
What distinguishes an unsupported answer from a stronger one?
Different practice example · weak: “Add another server; the system is reliable.”
Stronger: A second independently powered server can reduce a single-server outage. It does not remove a shared requirements error. Check failover under the relevant load before relying on it.
The stronger answer names a mechanism, its scope and inspectable evidence. It does not certify a real system. Your assessed answer must address this task’s own facts.
THIS WEEK · SUBMISSION CHECKLIST
Before you start
- Read the 4-point rubric first. It is the grading contract for this task.
- Save while you work. Download a backup before leaving a shared device.
- Commit Part A only when it represents your initial reasoning. Commitment freezes Part A and reveals STRESS; it is not Blackboard submission.
- After STRESS, complete REFIT + AI declaration + human review.
- Export the final PDF, open it and check it, upload it to Blackboard, then verify the Blackboard receipt.
For this staged exercise, do not read another student’s STRESS before committing. The new evidence opens automatically after you commit Part A. No unlock code is required. Your initial reasoning stays saved and read-only. The page sequences the task; it is not a secure examination system.
Identity
Loaded from the entry page. Drafts are separated by Student ID in this browser.
Submission details
Check the current deadline and submission instructions in the LMS.
ONE METHOD · TWO DIFFERENT CASES
From the classroom card to this assignment
The lecture has 20 slides and three short practice stations: claim + evidence; mechanism + limits; changed condition + revised decision. Here you transfer that reasoning to the separate assessed scenario below. Do not copy the practice answer or submit another full classroom report.
Unchanged: 4 raw points, existing deadline, local draft identity, confirmed Part A commitment, STRESS then REFIT, AI declaration and Blackboard submission. Already completed work does not need repeating merely because the lecture was updated.
No extra 20-rule forms are required. Accountability, evidence policy and the bounded final decision are already embedded in ACT + EVIDENCE, REFIT, the AI declaration and human review.
Five chapter objectives → existing evidence opportunities
These are local chapter objectives. They do not renumber the approved syllabus outcomes or establish an official national mapping. The lecturer judges correctness and sufficiency; a field being filled is not attainment.
| Chapter objective | Where it is practised / evidenced within this task |
|---|---|
| Objective 10.1 Distinguish the five properties using one example. | FIT + source application |
| Objective 10.2 Trace one failure through people, process and technology. | FIT + transfer question |
| Objective 10.3 Explain redundancy, diversity and common-cause failure. | BOUND + source application |
| Objective 10.4 Identify evidence from a dependable process. | ACT + EVIDENCE |
| Objective 10.5 Explain what formal verification assumes and what it cannot establish. | REFIT + EVIDENCE |
2 · PART A · 15 MINUTES
Assessed scenario · campus course registration
At 11:30, a fictional university's course-registration portal is experiencing intermittent errors during peak registration. Registration closes at 12:00. Two application servers support the portal, and automatic failover is enabled. The available failover test passed during a quiet period; no peak-load failover result is available. Current checks show that students can sign in and that confirmed registrations can be retrieved. No lost or duplicate registrations have been confirmed, but this has not yet been comprehensively checked. You are the duty software engineer. The registrar owns the registration deadline and may authorize an alternative submission route; you cannot change either policy yourself.
Your decision: Recommend one immediate operating plan: continue with stated controls, limit operation, or pause the affected function. Start with one governing dependability property, one observable boundary, one action with a responsible role, and one inspectable evidence item. Explain any mechanism you rely on. State what is known and what you would still need to verify. Your plan must address students' ability to complete registration and the integrity of confirmed registrations. There is no single required choice.
Keep the complete written response to about 180–260 focused words; use compact tables or notation. Include the source application and transfer answer in that budget. No external experiment is required. State facts, assumptions and proposed evidence separately. Quote or cite the assigned source precisely; explain its role. Report actual study time at the end.
A1 · FIT · 1 POINT
Select the leading dependability property, explain the consequence for users, and justify one relevant mechanism. Distinguish the property from the mechanism used to support it.
A2 · BOUND · 1 POINT
State an observable applicability condition and a trigger for reopening the decision. Name what remains unknown. Label any threshold you propose as proposed and requiring owner approval. Do not guess the later STRESS.
A3 · ACT · SCORED WITH EVIDENCE
State the action or verdict, its reason and operating condition, and the role responsible for it. This is your actual short artifact, not a promise to write one later.
A4 · EVIDENCE · SCORED WITH ACT
Name a record, test or measurement; say why it supports the decision, which version or conditions it must cover, and who checks it. Distinguish supplied scenario facts, assumptions, and evidence you still need. Label proposed tests or logs as requested evidence, not completed results. BOUND is the condition; EVIDENCE is how you check it.
ASSIGNED SOURCE APPLICATION · INCLUDED IN THE EXISTING RUBRIC
Write the source slide number, explain the concept in your own words, and identify the specific part of your artifact it supports or challenges. Use the assigned pages above. A citation alone is insufficient.
TRANSFER CHECK · SCORED WITH FIT
A proof establishes that a program satisfies its specification. Can you conclude that the service is safe in use? Name one assumption the proof does not establish.
Commit is not LMS submission. Confirmation freezes your original reasoning before the new constraint appears. Your final submission comes after REFIT and human review.