ASSIGNMENT 2 · CHAPTER 11
Reliability Engineering: measure before you claim
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 → MEASURE → BOUND → ACT + EVIDENCE
- Commit Part A
- STRESS → REFIT
- AI declaration + human review
- Export and submit in LMS
1 · WARM-UP · 5 MINUTES · NOT GRADED
A high uptime number can still hide the wrong failure.
A payment service was reachable for 99.99% of a test, but some payment requests returned an error. Does the availability number alone establish reliability of payment authorization?
Show / hide warm-up answer
No written warm-up response is required. Assignment 2 adds only one new burden: make the reliability claim measurable before you defend the operating decision.
Lecture guide and sentence stems
Use the lecture’s Chapter map to reconnect reliability, requirements, architecture, programming and measurement. Open Study & tools only when you need a source, rule or worksheet. You do not complete the 20-rule toolkit separately for this assignment. The task already embeds the relevant disciplines: choose the correct metric and denominator, label evidence honestly, state the boundary, name responsible roles, revise after STRESS, disclose AI assistance, read the rubric and finish with a bounded professional decision.
FIT: Failure means …; the metric that fits this service is … because …
MEASURE: Observed rate = …; compared with the stated target, this means …
BOUND: This conclusion is valid only while …; reopen if …
ACT + EVIDENCE: My release decision is …; the mechanism is …; the evidence is …
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: Reliability metrics and requirements: slides 19–24; Measurement and operational profiles: slides 70–75.
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 5-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 · 5 points
| Criterion | Scoring |
|---|---|
| FIT · 1 point | 1: Defines the relevant service failure, selects an appropriate reliability metric, and links the metric to the demand pattern. The short transfer answer must correctly apply the second concept; FIT and transfer together earn this single point. 0.75: The right failure definition and metric, but the link to the demand pattern is thin or the transfer answer is only partly correct. 0.5: A metric is named but does not match the failure or the demand pattern—for example, availability used for a per-demand failure—or the transfer answer is missing. 0: No reliability metric is justified, or the answer depends on invented measurements. |
| MEASURE · 1 point | 1: Correctly computes/interprets the observed failure rate and compares it with the stated requirement without overstating what the test proves. Apply one named required source concept to the artifact and explain the connection. 0.75: Correct calculation and comparison, but one qualification is missing—for example, the test conditions or the number of demands observed. 0.5: A calculation error, a wrong unit or observation window, or a comparison that treats the test result as proof that the requirement is met. 0: No calculation, a result that contradicts the given data, or an invented measurement. |
| BOUND · 1 point | 1: States the operating/test conditions that make the claim applicable and a clear trigger to reopen it. 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: Gives a feasible release/restrict/hold action, relevant reliability mechanism, responsible role, and inspectable evidence tied to the boundary. 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 what the new evidence does to the original claim, justifies RETAIN/REVISE/REPLACE, and gives a coherent final record. 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. |
The increase from Assignment 1 is deliberately small: one additional scored step — MEASURE. Any REFIT choice can still earn full credit when it is defended.
Learning-outcome alignment
This task supports CLO 1, 2 and 3 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: “The test passed, so reliability is guaranteed.”
Stronger: In a different example, 2 failures in 1,000 transactions gives 0.002 failures per transaction. This estimates the observed sample under its profile; it is not a confidence bound or a guarantee about production.
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 5-point rubric first. MEASURE is its own criterion in Assignment 2.
- Save while you work. Download a backup before leaving a shared device.
- Commit Part A only when FIT, MEASURE, BOUND, ACT + EVIDENCE and the source/transfer responses represent 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.
The new evidence opens automatically after you commit Part A. No unlock code is required. Your initial reasoning stays saved and read-only. The sequence is designed to preserve your first judgment; 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: 5 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. Measurement/falsification, accountability, evidence policy and the bounded final decision are already embedded in MEASURE, 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 11.1 Distinguish reliability from availability and explain how use and recovery affect them. | FIT + transfer question |
| Objective 11.2 Select and calculate POFOD, ROCOF, MTTF and AVAIL; write a measurable requirement. | MEASURE |
| Objective 11.3 Compare fault-tolerant architectures and justify a choice with its independence assumptions. | ACT + EVIDENCE + source application |
| Objective 11.4 Apply the eight dependable programming guidelines to a failure scenario. | ACT + EVIDENCE (source application) |
| Objective 11.5 Design a statistical reliability test using an operational profile and explain its limits. | BOUND + REFIT |
2 · PART A · 20 MINUTES
Assessed scenario · fictional university payment authorization service
A candidate release of a fictional university payment-authorization service will be used during registration week. The service handles many short, similar requests. The stated non-functional requirement is: ROCOF shall be no greater than 0.0005 authorization failures per payment transaction during registration service hours.
In the latest reliability test, the candidate processed 20,000 payment-authorization transactions and logged 6 authorization failures. The service was reachable for 99.98% of the test period. Two application instances run behind automatic failover. The test report says the dataset is “registration-like,” but the detailed operational-profile distribution is not included in the brief you received. No duplicate confirmed payments were found in the inspected sample, but the duplicate-payment audit is not yet complete.
You are the duty software engineer preparing a recommendation to the service owner. Choose one immediate action: release, release with explicit restrictions/conditions, or hold. Your recommendation must distinguish what the measured data supports from what remains unverified.
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
Define what counts as failure for the payment-authorization service. Select the primary metric (POFOD, ROCOF/MTTF, or AVAIL) and explain why it fits this usage pattern. You may mention a secondary metric, but identify one primary metric.
A2 · MEASURE · 1 POINT
Calculate the observed authorization failure rate from the supplied numbers. Compare it with the stated ROCOF requirement. Then state one sentence about what this comparison does not prove.
A3 · BOUND · 1 POINT
State the operational/test conditions your conclusion depends on and a trigger that would make you reopen it. Include at least one uncertainty visible in the scenario.
A4 · ACT + EVIDENCE · 1 POINT
State release / restricted release / hold, the condition behind it, one reliability mechanism you rely on, and the responsible role.
Name the relevant test/log/audit, the conditions it must cover, who checks it, and what evidence is still missing. Do not describe requested evidence as if it already exists.
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 primary and backup service share one specification and one power supply. Compare this arrangement with diverse implementations: name a shared cause that remains and one cost of diversity.
Commit is not LMS submission. Confirmation freezes FIT, MEASURE, BOUND, ACT and EVIDENCE before the new information appears.