IndexPDF Standards
Subject Indexing Rules
These are IndexPDF's standards for how subject indexing should be carried out.
The companion Subject Index Evaluation Standard 0.2 measures these rules through six scored dimensions and thirteen independent release gates.
1. Coverage and selectivity (Analysis)
Meaningful subjects
IPDF-ANA-01The index SHOULD provide access to substantively treated concepts, entities, processes, events, relationships, causes, consequences, arguments, conclusions, and reader tasks—not merely repeated words.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 5(a)–(h), 7.1.2
Cf.
- ISO 999:1996 § 4, Function of an index — ISO 999 covers the same retrieval function and conceptual access at a broader level.
Evidence
IPDF-ANA-02Every access point SHALL be supportable from source evidence establishing its subject, relationship, scope, chronology, attribution, and stance.
Related standards
Cf.
- ANSI/NISO Z39.4-2021 §§ 9, 9.1, 9.3 — Z39.4 connects headings and locators to indexed content; IndexPDF adds an explicit, auditable source-evidence obligation.
Coverage
IPDF-ANA-03Every essential and major source treatment SHALL have at least one useful access route unless it is explicitly excluded. A central omission is a critical defect.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 5(c), 7.1.2, 7.5.1
Selectivity
IPDF-ANA-04Passing mentions, contentless citations, and incidental names or examples SHALL NOT be treated like meaningful discussion.
A comparative fact or attributed observation may be substantive or mixed when it supplies independently useful information about the complete heading path. Its rhetorical form does not automatically make it weak.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 5(d), 9.2.2.2
Specificity
IPDF-ANA-05A heading SHOULD be specific enough to identify the treatment for the intended reader. It SHOULD NOT fragment coherent subjects into unfindable microentries or collapse distinct subjects under vague umbrella terms.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 5(f), 7.1, 7.5.2
2. Terminology and meaning (Vocabulary)
Reader-facing terminology
IPDF-VOC-01Preferred headings SHOULD use terminology that is faithful to the source and intelligible to likely readers.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 5(e), 7.1.5, 8.1–8.2
Variants
IPDF-VOC-02Synonyms, spelling variants, abbreviations, acronyms, former names, and likely user terms SHOULD reach the preferred concept through direct posting or a valid cross-reference.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 8.1, 8.2.2, 8.4, 8.7
- ANSI/NISO Z39.19-2005 (R2010) §§ 6.6.2, 8.2
Disambiguation
IPDF-VOC-03People, organizations, places, works, events, products, and scientific names SHALL be represented consistently and disambiguated where confusion is plausible.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 8.2.5, 8.3
- ANSI/NISO Z39.19-2005 (R2010) § 6.2.1
Fidelity
IPDF-VOC-04Headings SHALL preserve the source's attribution, negation, uncertainty, chronology, contested status, and degree of confidence. An index SHALL NOT convert a rejected, hypothetical, quoted, attributed, or qualified claim into an unqualified assertion.
Related standards
Cf.
- ANSI/NISO Z39.4-2021 §§ 2.6, 8 — Z39.4 requires care against introduced bias; IndexPDF extends fidelity to attribution, negation, uncertainty, chronology, contested status, and stance.
3. Entry architecture
Heading form
IPDF-ARC-01A heading SHOULD be concise, meaningful, and understandable without requiring the reader to reconstruct an unexplained keyword fragment. Grammar, spelling, capitalization, abbreviation, and punctuation SHOULD be internally consistent.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 2.6, 8.2, 9.1
Hierarchy
IPDF-ARC-02The baseline display SHALL use no more than a main heading and one subheading level. A third visible heading level is a publication-readiness failure under the baseline profile.
Related standards
Contra
- ANSI/NISO Z39.4-2021 §§ 9.1, 10.2.5.1, 10.2.5.3 — Z39.4 permits sub-subheadings and entries extending through several levels. The IndexPDF baseline permits only a main heading and one subheading level.
Cf.
- ANSI/NISO Z39.4-2021 § 10.2.5.2 — Z39.4 independently limits run-in layout to a main heading plus subheadings.
Subheadings
IPDF-ARC-03Sibling subheadings SHOULD be logically coordinate, grammatically parallel, and meaningful with their main heading. Subdivision SHOULD be used when it improves navigation, not solely because a locator count crosses a numerical threshold.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 9.1, 10.2.2, 11.5
Compound headings
IPDF-ARC-04A compound heading SHALL receive a locator only when the target supports the complete combined concept or relationship. If a page supports only separate components, those components must be indexed separately or the heading must be reformulated.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 8.2.4, 9.2.1.3
- ANSI/NISO Z39.19-2005 (R2010) § 7
Cf.
- ANSI/NISO Z39.4-2021 § 8.2.4 — IndexPDF applies the single-concept principle to the evidence at each locator, not only to the form of the heading.
Cross-references
IPDF-ARC-05A see reference SHOULD replace locators only from a genuinely nonpreferred heading to a valid target that provides the complete intended access. A see also reference SHOULD add useful related access.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 8.4, 8.6, 8.8.1.1, 8.8.1.3
Reference graph
IPDF-ARC-06Cross-references SHALL NOT be broken, self-referential, circular, or needlessly chained. Direct posting is preferred when it materially reduces reader effort without creating false equivalence.
Related standards
Cf.
- ANSI/NISO Z39.4-2021 §§ 8.8.1.3, 11.7 — Z39.4 governs cross-reference placement and arrangement; IndexPDF formalizes the references as a graph and expressly bars broken, self-referential, circular, and avoidably chained paths.
4. Locators
Existence
IPDF-LOC-01Every locator SHALL resolve to an existing destination in the declared source and locator scheme. Fabricated or nonexistent locators are critical defects.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 9.3, 9.3.1
Scope
IPDF-LOC-02Every locator SHALL point into indexable matter unless a recorded evaluation-policy exception applies.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 7.1.1, 9.3
Directness
IPDF-LOC-03A locator SHOULD identify the most direct useful destination available. A nearby page cannot supply meaning that is absent from the cited destination.
Related standards
With
- ANSI/NISO Z39.4-2021 § 9.3
Complete-path support
IPDF-LOC-04The destination SHALL provide independently useful information about the complete heading path. Treatment strength does not cure a mismatch in subject, relationship, scope, chronology, attribution, compound meaning, or stance.
Related standards
Cf.
- ANSI/NISO Z39.4-2021 §§ 9.1, 9.3 — Z39.4 requires headings to connect to the content they describe and locators to be direct and precise. IndexPDF makes support for the complete heading path an atomic requirement.
Ranges
IPDF-LOC-05A continuous range SHOULD begin and end within one continuous treatment. One displayed range counts as one displayed locator but expands into atomic page assignments for support auditing.
Related standards
With
- ANSI/NISO Z39.4-2021 § 9.1
Cf.
- DITA 2.0 index ranges Index range semantics — DITA defines explicit start and end markers for index ranges; IndexPDF additionally requires one continuous treatment and expands the displayed range for support auditing.
Review thresholds
IPDF-LOC-06More than six displayed locators under one undivided heading path or a continuous range longer than ten pages triggers editorial review. Exactly six displayed locators or a ten-page range does not trigger review.
A trigger is not automatically a defect. A scored architecture defect requires evidence that the entry combines conceptually distinct treatments, that a useful alternative organization exists, and that the current presentation materially harms retrieval.
Related standards
Cf.
- ANSI/NISO Z39.4-2021 § 9.1 — Z39.4 advises against long undifferentiated locator strings but sets no universal numeric limit. IndexPDF's six-locator and ten-page values are review triggers, not automatic defects.
Redundancy
IPDF-LOC-07Duplicate assignments, redundant overlapping ranges, and unexplained repeated access SHOULD be removed or justified.
Related standards
Cf.
- ANSI/NISO Z39.4-2021 §§ 8.8.1.1, 9.1 — Z39.4 sometimes favors double posting under alternative headings. IndexPDF therefore allows repeated access when justified while rejecting unexplained duplication and overlap.
5. Mechanics and presentation
Parseable structure
IPDF-MEC-01The delivered artifact SHALL be complete enough to identify headings, hierarchy, locators, ranges, cross-references, and termination reliably.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 9–10
Consistency
IPDF-MEC-02Spelling, capitalization, punctuation, locator style, indentation, and alphabetization SHOULD be consistently applied.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 8.2.2–8.2.3, 10.2, 11
- NISO TR03-1999 Alphabetical arrangement guidance
Readability
IPDF-MEC-03The index SHOULD be legible and scannable at its intended delivery size. Indentation, continuations, locator separation, cross-reference styling, and section labels should be unambiguous.
Related standards
With
- ANSI/NISO Z39.4-2021 §§ 10.1–10.5
Cf.
- ISO 999:1996 Presentation of indexes — ISO 999 covers index presentation broadly; the public catalogue does not support a clause-level equivalence claim.
Independent quality dimensions
IPDF-MEC-04Mechanical correctness does not compensate for inadequate coverage, poor selectivity, misleading headings, unsupported locators, or failed navigation.
Related standards
Cf.
- ANSI/NISO Z39.4-2021 §§ 2.6, 5, 7–10 — Z39.4 treats retrieval function, design, vocabulary, syntax, locators, and display as distinct concerns. IndexPDF expressly prevents good mechanics from compensating for failures in the other quality dimensions.