XwkOnt Core Ontology Specification

Local identifier: xwkont:ontology:core Editorial status: reviewed Created: 2026-07-01 Canonical artifact: this Markdown specification Companion representation: data/ontology/core.ttl Diagram source: docs/ontology/core-ontology.mmd Closed glossary: docs/ontology/core-glossary.md Logical axiom notes: docs/ontology/core-axioms.md

Purpose and Scope

This document defines the first XwkOnt core ontology specification. "Core ontology" means a conservative XwkOnt working vocabulary for organizing top-level foundational-ontology comparison, not a replacement for BFO, DOLCE, SUMO, UFO, or any other source ontology.

The core is intentionally limited to concepts and relationships that are repeatedly needed to compare foundational ontologies at a high level. It is a scaffolding artifact for later glossary closure, logical axiom work, validation, publication, and governance.

In Scope

• Candidate top-level concepts needed for crosswalk navigation and comparison.
• Candidate inheritance relationships among those concepts.
• Core relationship types with intended meanings.
• Domain and range notes where supportable from common foundational-ontology practice or prior XwkOnt crosswalk method.
• Explicit uncertainty where source ontologies diverge or evidence is insufficient.
• A lightweight RDF/RDFS/SKOS-compatible companion representation for structural review.
• A maintainable Mermaid diagram source.

Out of Scope

• Declaring a new authoritative foundational ontology.
• Resolving disagreements among source ontologies.
• Logical axiom-level definitions for every term; closed glossary definitions are documented in docs/ontology/core-glossary.md.
• OWL logical axioms, disjointness, property characteristics, cardinalities, and reasoner-grade constraints beyond the conservative notes in docs/ontology/core-axioms.md.
• Exhaustive source-specific mappings; concept crosswalks remain the place for detailed source comparison.
• Final URI/IRI publication policy.

Representation Decision

This Markdown document is the canonical ontology specification; data/ontology/core.ttl is an initial RDF/RDFS/SKOS-compatible companion representation.

Rationale:

• Markdown remains reviewable and repository-first, consistent with the information architecture's human-readable canonical approach.
• RDF was already adopted as the future graph data model, SKOS as the concept-centric vocabulary, and selected RDFS vocabulary as the lightweight vocabulary description layer.
• Turtle is compact, reviewable in Git, and structurally validatable without adopting OWL as the default modeling layer.
• OWL formalization is deferred to later logical-axiom work to avoid premature logical commitments.

This is an implementation-level decision rather than a new ADR because it applies the direction already accepted in ADR-0004 and does not change the project architecture.

Top-Level Concepts

Concept	Local identifier	Parent	Rationale	Status and uncertainty
Entity	xwkont:core:Entity	none	Broad comparison root needed because source foundational ontologies usually distinguish what exists or is modeled before subdividing it.	Candidate root; definition closure deferred.
Continuant	xwkont:core:Continuant	Entity	Needed to compare enduring entities such as objects, qualities, and roles across sources that distinguish continuants from occurrents or similar categories.	Candidate; not all source ontologies use this label or boundary.
Occurrent	xwkont:core:Occurrent	Entity	Needed to compare processes, events, and temporally unfolding entities across sources.	Candidate; event/process distinctions vary significantly.
Object	xwkont:core:Object	Continuant	A central comparison concept already identified in project scope and planned construction work.	Candidate; exact treatment differs across sources.
Quality	xwkont:core:Quality	Continuant	Needed because many foundational ontologies model dependent characteristics or qualities of bearers.	Candidate; dependence semantics deferred.
Role	xwkont:core:Role	Continuant	Needed because roles are prominent in applied ontology and differ from intrinsic object or quality categories.	Candidate; role, function, disposition, and relator boundaries deferred.
Process	xwkont:core:Process	Occurrent	Needed to compare temporally extended happenings, activities, or processes.	Candidate; process/event equivalence is not assumed.
Event	xwkont:core:Event	Occurrent	Needed because project scope explicitly names Event and several sources use event-like categories differently from process.	Candidate sibling of Process for now; formal relation to Process deferred.
Relation	xwkont:core:Relation	Entity	Needed to document first-class relation concepts and relationship types used in comparison.	Candidate; whether relations are entities is source-dependent and uncertain.
Information Artifact	xwkont:core:InformationArtifact	Entity	Needed for XwkOnt's own references, definitions, mappings, and specifications without treating them as source ontology commitments.	Candidate support concept; may move to metadata vocabulary later.
Abstract	xwkont:core:Abstract	Entity	Added for the 0.2.0 batch (ADR-0018); needed to compare entities lacking spatiotemporal location or embodiment.	Candidate; modeled as a class pair sibling to Continuant/Occurrent per maintainer-confirmed recommendation (docs/crosswalks/concepts/abstract-concrete.md).
Concrete	xwkont:core:Concrete	Entity	Added for the 0.2.0 batch; needed to compare entities with spatiotemporal location or embodiment.	Candidate; modeled as Abstract's sibling class pair per the same recommendation.
Universal	xwkont:core:Universal	Entity	Added for the 0.2.0 batch; needed to compare type/kind/category concepts distinct from a particular individual.	Candidate; modeled as a direct Entity subclass paralleling GFO's own top-level Category/Individual split (docs/crosswalks/concepts/universal-type.md); SUMO's narrower Abstract-subtype framing and UFO's rigidity typology are not yet formalized.
Time	xwkont:core:Time	Entity	Added for the 0.2.0 batch; needed to compare temporal region/instant/interval concepts.	Candidate; modeled as a direct Entity subclass since most sources with a Time category treat it as independent of Continuant/Occurrent (docs/crosswalks/concepts/time.md); BFO is the sole exception.
Space	xwkont:core:Space	Entity	Added for the 0.2.0 batch; needed to compare spatial region/place concepts.	Candidate; modeled as a direct Entity subclass consistent with Time, though source classification diverges more here (docs/crosswalks/concepts/space.md).
Aggregate	xwkont:core:Aggregate	Continuant	Added for the 0.2.0 batch; needed to compare uniform-membership-criterion pluralities distinct from Object.	Candidate; one of two sibling sub-concepts (with Sum) per maintainer-confirmed recommendation, reflecting an even source split on unity-criterion strictness (docs/crosswalks/concepts/mereology-parthood-aggregate.md).
Sum	xwkont:core:Sum	Continuant	Added for the 0.2.0 batch; needed to compare criterion-free mereological sums distinct from Aggregate.	Candidate; Aggregate's sibling sub-concept per the same recommendation.
Boundary	xwkont:core:Boundary	Continuant	Added for the 0.2.0 batch; needed to compare part-of-host, fiat-demarcated boundary concepts.	Candidate; one of two sibling sub-concepts (with Site) per maintainer-confirmed recommendation, reflecting BFO's and DOLCE's independently-converging split (docs/crosswalks/concepts/boundary-site.md).
Site	xwkont:core:Site	Continuant	Added for the 0.2.0 batch; needed to compare not-part-of-host dependent place concepts.	Candidate; Boundary's sibling sub-concept per the same recommendation.
Quantity	xwkont:core:Quantity	Concrete	Added for the 0.2.0 batch; needed to compare amount-of-matter/quantity concepts.	Candidate; covers several related but distinct source-ontology senses that this placement does not assume resolve to one class (docs/crosswalks/concepts/quantity-amount-of-matter.md); modeled under Concrete per the DOLCE/UFO/GFO majority.
Proposition	xwkont:core:Proposition	Abstract	Added for the 0.2.0 batch; needed to compare purely combinatorial, representation-independent content concepts.	Candidate; modeled under Abstract following all three confirmed sources' (DOLCE, SUMO, YAMATO) own treatment (docs/crosswalks/concepts/proposition-content.md).
Change	xwkont:core:Change	Entity	Added for the 0.3.0 batch (ADR-0021); needed to compare alteration/transition concepts.	Candidate; modeled as a direct Entity subclass since sources diverge on Continuant/Occurrent framing — GFO's Change is disjoint with its own Process class, SUMO's InternalChange is typically a Process subtype (docs/crosswalks/concepts/change.md).
Continuous	xwkont:core:Continuous	Entity	Added for the 0.3.0 batch; needed to compare gapless/densely-ordered concepts.	Candidate; one of two sibling sub-concepts (with Discrete) per maintainer-confirmed recommendation, reflecting GFO's own sibling-class split under its top-level Individual category (docs/crosswalks/concepts/continuous-discrete.md).
Discrete	xwkont:core:Discrete	Entity	Added for the 0.3.0 batch; needed to compare separated/countable/gap-bounded concepts.	Candidate; Continuous's sibling sub-concept per the same recommendation.
Ontological Level / Stratum	xwkont:core:OntologicalLevelStratum	Entity	Added for the 0.3.0 batch; needed to compare level/stratum/layer classifier concepts.	Candidate; modeled as a direct Entity subclass and single umbrella class, a meta-level classifier orthogonal to Continuant/Occurrent, paralleling Universal's treatment; source GFO's Ontological_layer further splits into unformalized Stratum/Level branches (docs/crosswalks/concepts/ontological-level-stratum.md).
List / Sequence	xwkont:core:ListSequence	Entity	Added for the 0.3.0 batch; needed to compare ordered-collection concepts.	Candidate; modeled as a direct Entity subclass since sources diverge — SUMO places List under Abstract, GUM places OrderedObject under its own concrete DecomposableObject lineage (docs/crosswalks/concepts/list-sequence.md).
Mind / Conscious Being / Agent	xwkont:core:MindConsciousBeingAgent	Continuant	Added for the 0.3.0 batch; needed to compare mind/conscious-being/agent concepts.	Candidate; modeled as a sibling of Object under Continuant, reflecting a convergent cross-source pattern (SUMO, DOLCE, YAMATO) that specializes an object-like layer without folding into it (docs/crosswalks/concepts/mind-conscious-being-agent.md).
Non-physical Object	xwkont:core:NonPhysicalObject	Continuant	Added for the 0.3.0 batch; needed to compare non-physical endurant concepts.	Candidate; modeled under Continuant as a single umbrella class only — DOLCE-Lite's own base module supports only the broader non-physical-object class, not a separate Social Object split, which lives only in DOLCE's DnS extension (docs/crosswalks/concepts/non-physical-social-object.md).
Disposition	xwkont:core:Disposition	Continuant	Added for the 0.3.0 batch; needed to compare tendency/capacity/potential concepts.	Candidate; modeled as a sibling of Role under Continuant, following BFO's own treatment as a specifically dependent continuant; BFO's own Function subtype is not split out separately, not yet cross-source-confirmed (docs/crosswalks/concepts/disposition-capacity.md).
Modality	xwkont:core:Modality	Quality	Added for the 0.3.0 batch; needed to compare necessity/possibility/contingency-qualifying concepts.	Candidate; modeled under Quality following GUM's own direct structural treatment (ModalQuality as subclass of SimpleQuality), consistent with SUMO's AlethicAttribute (docs/crosswalks/concepts/modality.md).
Symbol / Sign / Representation	xwkont:core:SymbolSignRepresentation	Universal	Added for the 0.3.0 batch (last of the nine, session-059); needed to compare symbol/sign/representation-form type concepts.	Candidate; class-plus-relation-family resolution (maintainer-confirmed) of the single-class-vs-family question the concept's own Uncertainty section flagged — this class covers GFO's type-side Symbol_structure evidence (rdfs:subClassOf Category, paralleling Universal's own GFO-Category parallel); GUM's relation-type evidence (Symbolization family) is covered instead by the new symbolizes/symbolizedBy relation pair, mirroring the Role/bearsRole/roleOf pattern (docs/crosswalks/concepts/symbol-sign-representation.md).
Situation / State of Affairs	xwkont:core:SituationStateOfAffairs	Continuant	Added for the 0.2.0 batch (placed last, session-060); needed to compare configuration/comprehended-whole concepts.	Candidate; modeled as a sibling of Object under Continuant, following GFO's own Presential-side Situation and DOLCE's own non-agentive-social-object placement of situation (DnS module) — both continuant-committing sources place their evidence on the continuant side. Resolves the three-way sense split external review flagged: this class covers only the configuration/comprehended-whole sense, not DOLCE's occurrent State or TUpper's unreified fluent-like state (docs/crosswalks/concepts/situation-state-of-affairs.md).

Candidate Inheritance Relationships

Subject	Relationship	Object	Rationale	Uncertainty
Continuant	rdfs:subClassOf	Entity	Common high-level organizing distinction for comparison.	Label and formal semantics vary by source.
Occurrent	rdfs:subClassOf	Entity	Common high-level organizing distinction for comparison.	Label and formal semantics vary by source.
Object	rdfs:subClassOf	Continuant	Objects are treated as continuant-like comparison targets in the first core.	Source-specific boundaries require crosswalk evidence.
Quality	rdfs:subClassOf	Continuant	Qualities are compared as dependent continuant-like entities in the first core.	Dependence axioms deferred.
Role	rdfs:subClassOf	Continuant	Roles are compared as dependent/contextual continuant-like entities in the first core.	Role/function/disposition distinctions deferred.
Process	rdfs:subClassOf	Occurrent	Processes are treated as occurrent-like comparison targets.	Relation to Event remains open.
Event	rdfs:subClassOf	Occurrent	Events are treated as occurrent-like comparison targets.	Relation to Process remains open.
Relation	rdfs:subClassOf	Entity	Lets relationship concepts be discussed in the same scaffold.	Some source ontologies may not reify relations this way.
Information Artifact	rdfs:subClassOf	Entity	Supports XwkOnt records and evidence artifacts.	May be refactored into a separate metadata layer.
Abstract	rdfs:subClassOf	Entity	Class-pair sibling of Continuant/Occurrent for entities lacking spatiotemporal location.	Maintainer-confirmed recommendation; boundary with Concrete is source-dependent.
Concrete	rdfs:subClassOf	Entity	Class-pair sibling of Continuant/Occurrent for entities with spatiotemporal location.	Maintainer-confirmed recommendation; boundary with Abstract is source-dependent.
Universal	rdfs:subClassOf	Entity	Direct Entity subclass paralleling GFO's Category/Individual top-level split.	SUMO's narrower Abstract-subtype framing not yet formalized.
Time	rdfs:subClassOf	Entity	Direct Entity subclass since most sources treat Time as independent of Continuant/Occurrent.	BFO alone classifies Time as occurrent.
Space	rdfs:subClassOf	Entity	Direct Entity subclass, consistent with Time's placement.	Source classification diverges more for Space than Time (three-way split).
Aggregate	rdfs:subClassOf	Continuant	Sibling of Object for uniform-membership-criterion pluralities.	One of two sibling sub-concepts with Sum; even source split on unity-criterion strictness.
Sum	rdfs:subClassOf	Continuant	Sibling of Object/Aggregate for criterion-free mereological sums.	Aggregate's sibling sub-concept.
Boundary	rdfs:subClassOf	Continuant	Part-of-host, fiat-demarcated boundary concepts.	One of two sibling sub-concepts with Site; reflects BFO/DOLCE convergence.
Site	rdfs:subClassOf	Continuant	Not-part-of-host dependent place concepts.	Boundary's sibling sub-concept.
Quantity	rdfs:subClassOf	Concrete	Amount-of-matter/quantity concepts, modeled under Concrete per the DOLCE/UFO/GFO majority.	Covers multiple related but distinct source senses; SUMO/YAMATO diverge.
Proposition	rdfs:subClassOf	Abstract	Purely combinatorial, representation-independent content.	Follows DOLCE/SUMO/YAMATO's own Abstract-subtype treatment.
Change	rdfs:subClassOf	Entity	Direct Entity subclass since sources diverge on Continuant/Occurrent framing.	GFO's Change is disjoint with Process; SUMO's InternalChange is typically a Process subtype.
Continuous	rdfs:subClassOf	Entity	Sibling of Discrete for gapless/densely-ordered concepts.	One of two sibling sub-concepts with Discrete; reflects GFO's own sibling-class split.
Discrete	rdfs:subClassOf	Entity	Sibling of Continuous for separated/countable/gap-bounded concepts.	Continuous's sibling sub-concept.
Ontological Level / Stratum	rdfs:subClassOf	Entity	Direct Entity subclass, meta-level classifier orthogonal to Continuant/Occurrent.	Single umbrella class; GFO's own Stratum/Level branches not yet formalized.
List / Sequence	rdfs:subClassOf	Entity	Direct Entity subclass since sources diverge on Abstract/Concrete framing.	SUMO places List under Abstract; GUM places OrderedObject under a concrete lineage.
Mind / Conscious Being / Agent	rdfs:subClassOf	Continuant	Sibling of Object for mind/conscious-being/agent concepts.	Convergent cross-source object-layer pattern (SUMO, DOLCE, YAMATO).
Non-physical Object	rdfs:subClassOf	Continuant	Single umbrella class for non-physical endurants.	DOLCE-Lite's base module supports only the broader class, not a Social Object split.
Disposition	rdfs:subClassOf	Continuant	Sibling of Role for tendency/capacity/potential concepts.	Follows BFO's specifically-dependent-continuant treatment; Function subtype not split out.
Modality	rdfs:subClassOf	Quality	Necessity/possibility/contingency-qualifying concepts.	Follows GUM's ModalQuality-under-SimpleQuality treatment, consistent with SUMO's AlethicAttribute.
Symbol / Sign / Representation	rdfs:subClassOf	Universal	Symbol/sign/representation-form type concepts, covering GFO's Symbol_structure evidence.	Maintainer-confirmed class-plus-relation-family resolution; GUM's relation-type evidence is covered by symbolizes/symbolizedBy instead.
Situation / State of Affairs	rdfs:subClassOf	Continuant	Sibling of Object for configuration/comprehended-whole concepts.	Follows GFO's Presential-side and DOLCE's non-agentive-social-object placement; resolves the three-way sense split by excluding DOLCE's occurrent State and TUpper's unreified state.

Core Relationship Types

Relationship	Local identifier	Intended meaning	Candidate domain	Candidate range	Rationale	Status and uncertainty
has part	xwkont:core:hasPart	A whole includes another entity as a part.	Entity	Entity	Part-whole comparison is broadly needed across foundational ontologies.	Structural only; mereological axioms deferred.
part of	xwkont:core:partOf	An entity is part of a larger entity.	Entity	Entity	Inverse navigation for part-whole notes.	Inverse formalization deferred.
participates in	xwkont:core:participatesIn	A continuant is involved in an occurrent.	Continuant	Occurrent	Needed to relate objects, roles, and other continuants to processes/events.	Domain/range are candidate only.
has participant	xwkont:core:hasParticipant	An occurrent involves a continuant.	Occurrent	Continuant	Inverse navigation for participation.	Inverse formalization deferred.
has quality	xwkont:core:hasQuality	An entity bears or is characterized by a quality.	Entity	Quality	Needed to compare quality-bearing patterns.	Whether all entities can bear qualities is deferred.
quality of	xwkont:core:qualityOf	A quality characterizes or depends on a bearer.	Quality	Entity	Inverse navigation for quality comparison.	Dependence semantics deferred.
bears role	xwkont:core:bearsRole	An entity has a role in some context.	Entity	Role	Needed for role comparison.	Context qualification deferred.
role of	xwkont:core:roleOf	A role is borne by an entity.	Role	Entity	Inverse navigation for role comparison.	Dependence and context axioms deferred.
symbolizes	xwkont:core:symbolizes	A symbol, sign, or representation-form entity symbolizes another entity.	Entity	Entity	Needed for GUM's Symbolization relation family (Symbolization/Signification/NameOf/NameRelation), which XwkOnt does not further subdivide.	GUM's own SYMBOL/SYMBOLIZED domain-range roles not separately formalized.
symbolized by	xwkont:core:symbolizedBy	An entity is symbolized by a symbol, sign, or representation-form entity.	Entity	Entity	Inverse navigation for symbolization comparison.	Inverse formalization deferred.
depends on	xwkont:core:dependsOn	One entity depends on another in some sense.	Entity	Entity	Captures common dependency language without committing to a subtype.	Dependency kinds deferred.
maps to	xwkont:core:mapsTo	An XwkOnt concept or relationship has a candidate mapping to another concept or relationship.	Entity	Entity	Bridges core ontology work with crosswalk methodology.	Use detailed mapping categories in crosswalk artifacts.
documented by	xwkont:core:documentedBy	A concept, relationship, or claim is documented by an information artifact.	Entity	Information Artifact	Supports repository-first provenance.	Exact provenance model deferred to publication/governance work.

Structural Consistency Rules

The initial representation is considered structurally consistent when:

1. Every local class used as a domain, range, or superclass is declared.
2. Every local property referenced in the specification is declared.
3. Every subclass edge connects declared classes.
4. Every property with a candidate domain or range points to a declared class.
5. The Turtle companion parses as RDF.
6. No OWL-only constructs are required for this artifact.

Unresolved Modeling Questions

Question	Impact	Assigned follow-up
Are Process and Event siblings, overlapping concepts, or should one specialize the other?	Affects top-level hierarchy and source crosswalks.	Glossary for evidence; axiom review for formalization.
Should Relation remain under Entity or move into a separate vocabulary layer?	Affects whether relationship concepts are modeled as first-class core concepts.	Later architecture review.
Should Information Artifact be part of the core ontology or only metadata/provenance infrastructure?	Affects boundary between ontology content and repository metadata.	Validation work or publication planning.
Which dependency subtypes are needed: existential, generic, specific, historical, or contextual?	Affects qualities, roles, and participation semantics.	Later logical-axiom work.
What are the exact source correspondences for each top-level concept across BFO, DOLCE, SUMO, and UFO?	Affects confidence and acceptance of candidate concepts.	Glossary and concept crosswalk work.
Should mapsTo be retained in the core ontology or replaced entirely by SKOS and crosswalk mapping records?	Affects machine-readable export design.	Later logical-axiom work or publication planning.

Deferred Formalization Work

A conservative logical review was completed in docs/ontology/core-axioms.md. The following remain deferred:

• OWL class axioms, disjointness, property inverses, transitivity, and constraints.
• Competency questions and example knowledge base validation.
• URI/IRI publication policy and namespace governance.
• Rendered diagrams and publication-ready documentation.

Validation Notes

This specification validates the companion Turtle file for parseability and verifies that all local domain, range, and subclass references resolve to declared local classes. This validation is structural only; it does not prove logical consistency. The closed glossary adds a dependency graph for the terms used in this specification. The axiom review adds conservative logical axiom notes, classifies candidate inheritance and relationship axioms, and removes RDFS domain/range commitments from the transitional mapsTo property.