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Semester Storage Estimator

Run the Semester Storage Estimator Fullscreen

About This MicroSim

LRS-Lite keeps each student's learning record in a small database inside the browser, so the design has to show that a semester of statements is small enough to live there. This estimator repeats the design's back-of-the-envelope arithmetic. You set the daily activity of one student and the emission mode, and the chart shows the raw and gzipped size of a semester against the 10 MB budget.

The model uses the design's own rules:

  • Summary mode statements per day = page reads + sim sessions + quiz answers.
  • Full mode statements per day = page reads + quiz answers + sim sessions × (drags + 2).
  • Raw size = statements × 980 bytes. Gzipped size ≈ raw ÷ 10 (the design's approximate ratio).
  • Headroom = 10 MB ÷ gzipped size.

The figures are modelled from synthetic statements, not from real learners. The Load design cases button steps through the four measured cases from the chapter's table and shows the measured values next to the model's. The measured gzip ratio is about 10 times for summary statements but about 15 to 17 times for Full mode, so "÷ 10" is only an approximation.

Learning objective: The learner will calculate the statement count and storage footprint of a semester from activity assumptions, and judge how much headroom remains under a 10 MB limit.

Bloom's taxonomy level: Apply (verb: calculate)

How to Use

  1. Start with the defaults, the design's typical student: 6 page reads, 4 sim sessions and 15 quiz answers per active day for 90 days, in Summary mode. Check the readout: 25 statements a day, 2,250 per semester, about 0.22 MB gzipped, about 45 times headroom.
  2. Hover a bar to see its exact value and the formula that produced it.
  3. Press Full to switch the emission mode. Every sim session now costs drags + 2 statements. Move the Drags / session slider and watch the bars.
  4. Press Load design cases repeatedly to snap the controls to each of the four cases in the chapter's table. Compare the model's gzip figure with the measured one.
  5. Try to find settings that cross 6 MB gzipped (60% of the budget) or 10 MB. Which mode and which slider does it take?

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

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<iframe src="https://dmccreary.github.io/microsims/sims/lite-semester-storage-estimator/main.html"
        height="602px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Audience

Teachers, instructional designers, learning-technology developers and learning-analytics practitioners (college undergraduate and professional development).

Duration

15 minutes

Prerequisites

  • What an xAPI statement is (Chapter 16)
  • The difference between Full mode and Compact (summary) mode (Chapter 22)
  • Megabytes as 1,000,000 bytes

Activities

  1. Check the worked example (3 min): With the defaults, compute the statements per day, the statements per semester, the raw size and the gzipped size by hand. Confirm each number against the readout.
  2. Full mode (4 min): Switch to Full. Before touching anything, predict the statements per day for 40 drags per session. Then verify: 6 + 15 + 4 × (40 + 2) = 189.
  3. Design cases (4 min): Step through the four design cases. For each, record the model's gzip size and the measured one. Explain why the model overstates Full mode.
  4. Stress test (4 min): Find the smallest number of drags per session that pushes a heavy student in Full mode over 6 MB gzipped. Discuss whether the 10 MB budget is a working constraint or a safety rail.

Assessment

  • Given reads, sessions, answers, days and mode, the learner computes the statements per semester and the gzipped size to within rounding.
  • The learner states the headroom multiple for a case and explains what it means.
  • The learner explains which two levers (summarizing and compression) keep a semester small.

References

  1. Experience API - Wikipedia. The statement format whose size this estimator models.
  2. xAPI specification - Advanced Distributed Learning (ADL) on GitHub. The structure of a statement.
  3. gzip - Wikipedia. The compression format used to size the stored segments.
  4. Chart.js bar chart documentation - Chart.js. The library used to draw the chart.