Tim Allison created TIKA-4794:
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Summary: Normalize/simplify metadata keys in 4.x
Key: TIKA-4794
URL: https://issues.apache.org/jira/browse/TIKA-4794
Project: Tika
Issue Type: Task
Reporter: Tim Allison
*Background*
Tika's metadata keys are inconsistent, and 4.0.0 is the last free break until
5.0 (whatever ships is frozen for the 4.x line):
* Tika's own keys are scattered across ~8 prefixes (X-TIKA:, tika:, tika_pg:,
rendering:, signature:, imagereader:, bare hasSignature/embeddedResourceType),
with 3+ casings inside X-TIKA: alone (snake, camel, Title-Hyphen, UPPER
sub-namespaces).
* resourceName shipped half-migrated (bare → X-TIKA:resourceName) — the worst
state.
* The metadata object is also a control plane (media type drives routing,
resourceName drives detection, X-TIKA:* carries provenance/digests), but the
boundary is convention only: a crafted file can inject or overwrite Tika's own
keys.
* Format namespaces mix casings; QuattroPro reuses WordPerfect's prefix
(collision); there's no rule for "is this key Tika's or the file's".
Options
# Leave as-is. Ship the inconsistency + half-migrated resourceName +
convention-only boundary; frozen until 5.x
# tk:. Consolidate every Tika-asserted key under one kebab-cased tk: prefix;
finish resourceName → tk:resource-name; add a reserved-namespace trust
boundary. Format namespaces untouched.
# tk: + kebab. Everything in (2), plus apply the casing rule inside the
format namespaces.
*Guiding principles (2 and 3)*
1. Who asserted the key? Tika-computed → owned, normalized, trusted.
File/standard-authored → verbatim (the spelling/capitalization is the interop
contract).
2. Match enforcement to stakes. Control-plane / Tika-native keys → reserved,
writable only via a Property; cosmetic drift → convention.
3. Casing follows key-name authorship, not the namespace (the prefix is just
the domain). Tika coined the name → kebab; a standard/file authored it →
verbatim.
4. Clean 3→4 break, documented with a migration table; no auto-remap
machinery.
*2 — tk: (rationale + consistency)*
One prefix, one casing for everything Tika asserts, replacing the 8 scattered
prefixes and their mixed casings; resourceName finished. tk: (and legacy
X-TIKA:) become reserved: a String write to them is dropped unless trusted, so
a scraped file can't forge Tika's routing/provenance/digest/content keys or
inject fake tk:chunks embeddings — enforced once in tika-core, not per-parser
discipline. Consistency: any Tika key is now predictable (tk: + kebab), and the
trust boundary is mechanism rather than convention.
*3 — tk: + kebab (rationale + consistency)*
Extends "Tika-coined → kebab" into the format namespaces (e.g.
pdf:hasMarkedContent → pdf:has-marked-content, zip:compressedSize →
zip:compressed-size, access_permission: → access-permission:). Names from a
standard stay verbatim (dc:, xmp:, EXIF/tiff:, MAPI, email headers, ECMA-376
OOXML props, PDF/A/X sub-namespaces) — re-casing them would break
round-trip/interop. Also fixes the QuattroPro/WordPerfect prefix collision.
Consistency: a Tika-authored key is kebab wherever it lives (under tk: or a
format prefix); a standard/file key keeps its source spelling — one rule
answers casing everywhere.
If we did steps 2 or 3, we'd probably want to release a 4.0.0-beta-2
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