Research note · Research note 06 — current edition

A Taxonomy of Web-Data Failure Modes

AG

Written by Aaron Grainger

Independent Content Strategist & Product-Marketing Writer · Published Aug 19, 2025

Primary audience
Product managers building AI features
Also useful for
AI engineers and technical founders
Tone
Authoritative
Reading time
2 min
Published
Aug 19, 2025

Abstract

Debugging a web-data pipeline is easier when failures have names. This note proposes a working taxonomy across five layers — access, retrieval, normalization, extraction, and interpretation — and notes which layer each symptom usually belongs to.

Key questions

  • Where do the symptoms of a bad output actually originate?
  • Which failures are detectable automatically and which require review?
  • What is the cheapest assertion for each class?

How this note was developed

  • Collection of observed failures during prototype construction.
  • Grouping by originating layer rather than by symptom.
  • Analytical framework; no frequency data is presented.

Central arguments

01Access failures: blocked, throttled, gated, or geo-restricted

Usually loud, sometimes disguised as a 200 with a challenge page. Cheapest assertion: detect known interstitial patterns and content length far below the page-type norm.

02Retrieval failures: empty shells, partial renders, soft 404s

The request succeeded and the content did not arrive. Assertion: require a minimum of meaningful text and the presence of an expected structural element such as a heading.

03Normalization failures: over-stripping and under-stripping

Tables and code blocks dropped, or navigation retained. Assertion: compare retained element counts against the page-type profile and flag outliers for review.

04Extraction failures: wrong field, plausible invention, unit confusion

The most dangerous class, because output looks valid. Assertion: schema validation plus a required source excerpt for each extracted value.

05Interpretation failures: correct data, wrong conclusion

A stale page treated as current, a regional price treated as global, one vendor's claim treated as fact. No automated assertion suffices; this layer needs review policy and explicit provenance display.

Limitations

  • The taxonomy is a working tool, not an exhaustive or validated classification.
  • Layer boundaries blur — a soft 404 can equally be described as an access or retrieval failure.
failure modesqualitydebugging

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Version history

Current: 1.0 · Published

  1. 1.0Aug 19, 2025First published.

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