NAF (NLP Annotation Format)

Model

NLP Annotation Format (NAF)

Origin

NewsReader project

Specification

NAF v3

Key Reference

Fokkens et al. 2014

Overview

NAF is a layered stand-off annotation format designed for NLP pipeline interoperability. It organizes annotations into explicitly named layers (text, terms, entities, chunks, dependencies, constituency, SRL, coreference, opinions, temporal expressions, factuality, etc.). NAF was developed as a successor to KAF (Kyoto Annotation Format) and is used in tools like the NewsReader pipeline.

Layer-by-Layer Mapping

Text Layer

NAF Element	Layers Equivalent	Notes
<text> layer	pub.layers.expression.text	Raw text.
<wf> (word form)	pub.layers.expression (kind: token)	Tokens with character offsets. @offset → token.textSpan.start; @length → derived from text; @sent → sentence grouping.

Terms Layer

NAF Element	Layers Equivalent	Notes
<terms> layer	pub.layers.annotation#annotationLayer(kind="token-tag")	Term-level annotations.
<term>	Multiple annotation objects across layers	NAF's <term> bundles POS, lemma, morphology, and sense into a single element. Layers separates these into distinct annotation layers: subkind="pos" for @pos, subkind="lemma" for @lemma, subkind="morph" for @morphofeat, subkind="sense" for <externalRef>.
<term @pos>	annotationLayer(kind="token-tag", subkind="pos")	POS tag.
<term @lemma>	annotationLayer(kind="token-tag", subkind="lemma")	Lemma.
<term @morphofeat>	annotationLayer(kind="token-tag", subkind="morph")	Morphological features.
<term><sentiment>	annotationLayer(kind="token-tag", subkind="sentiment") or features	Term-level sentiment.
<span> (within term)	annotation.anchor.tokenRefSequence	Multi-word terms spanning multiple word forms.

Entity Layer

NAF Element	Layers Equivalent	Notes
<entities> layer	annotationLayer(kind="span", subkind="entity-mention")	Entity mention layer.
<entity @type>	annotation.label	Entity type (PER, ORG, LOC, etc.).
<references><span>	annotation.anchor.tokenRefSequence	Token references for entity span.
<externalRef>	annotation.knowledgeRefs	Links to DBpedia, Wikipedia, etc. @resource → knowledgeRef.source; @reference → knowledgeRef.identifier.

Dependency Layer

NAF Element	Layers Equivalent	Notes
<deps> layer	annotationLayer(kind="graph", subkind="dependency")	Dependency parse.
<dep @rfunc>	annotation.label	Dependency relation label.
<dep @from @to>	annotation.headIndex / annotation.tokenIndex	Governor and dependent.

Constituency Layer

NAF Element	Layers Equivalent	Notes
<constituency> layer	annotationLayer(kind="tree", subkind="constituency")	Constituency parse.
<tree>	One parse tree per sentence	Tree structure.
<nt @label> (non-terminal)	annotation with parentId/childIds	Non-terminal node. @label → annotation.label.
<t> (terminal)	annotation with tokenIndex	Terminal node linked to token.
<edge>	Implicit in parentId/childIds relationships	Tree edges encoded in parent-child structure.

Chunk Layer

NAF Element	Layers Equivalent	Notes
<chunks> layer	annotationLayer(kind="token-tag", subkind="chunk") or annotationLayer(kind="span")	Chunking.
<chunk @phrase>	annotation.label	Chunk type (NP, VP, PP, etc.).

SRL Layer

NAF Element	Layers Equivalent	Notes
<srl> layer	annotationLayer(kind="span", subkind="frame")	Semantic role labeling.
<predicate>	annotation (frame instance)	@uri → annotation.knowledgeRefs (PropBank/NomBank).
<role @semRole>	argumentRef.role	Semantic role label (ARG0, ARG1, ARGM-TMP, etc.).
<role><span>	argumentRef.annotationId → span annotation	The span filling the role.

Coreference Layer

NAF Element	Layers Equivalent	Notes
<coreferences> layer	pub.layers.annotation#clusterSet(kind="coreference")	Coreference chains.
<coref>	cluster	A coreference chain. @type → cluster.features.
<span> (within coref)	cluster.memberIds → annotation UUIDs	Mentions in the chain.

Opinion Layer

NAF Element	Layers Equivalent	Notes
<opinions> layer	annotationLayer(kind="span", subkind="sentiment")	Opinion/sentiment annotation.
<opinion>	annotation	Opinion instance.
<opinion_holder>	argumentRef with role="holder"	The opinion holder.
<opinion_target>	argumentRef with role="target"	The opinion target.
<opinion_expression @polarity>	annotation.label (polarity) + anchor	The evaluative expression.

Temporal Expression Layer

NAF Element	Layers Equivalent	Notes
<timeExpressions> layer	annotationLayer(kind="span", subkind="temporal-expression")	TimeML TIMEX3 expressions.
<timex3 @type @value>	annotation.label (type) + annotation.value (normalized)	@type → label (DATE, TIME, DURATION, SET); @value → normalized value.

Factuality Layer

NAF Element	Layers Equivalent	Notes
<factualities> layer	annotationLayer(kind="span") with custom subkind via subkindUri	Factuality assessment (certain, probable, possible, counterfactual).
<factuality @prediction>	annotation.label	Factuality value.

NAF Header and Provenance

NAF Feature	Layers Equivalent	Notes
<nafHeader>	pub.layers.expression metadata + features	Document metadata.
<linguisticProcessors>	pub.layers.defs#annotationMetadata.tool per layer	Each layer records its producing tool.
<lp @name @version @timestamp>	annotationMetadata fields	Tool name, version, and timestamp.
<fileDesc>	Expression fields	File description.
<public>	Expression sourceUrl	Public identifier/URI.