Foundations & architecture

The layer a generator cannot emit — why the model is shaped as it is. Four foundational frames govern every term in the ontology: the UFO meta-category each class commits to, the three-graph separation that keeps meaning, validation, and advice apart, the six bounded contexts the standard partitions the industry into, and the inference / validation boundary that fixes what is entailed versus what is merely checked. Counts below are read at build time from the committed TTL corpus at source/03-standards/ontology/.

UFO meta-category legend

Every OPDA class commits to a Unified Foundational Ontology (UFO) stereotype with OntoClean meta-properties (rigidity, identity, dependence). This frame leads the reference — before any term table — because the stereotype determines how a thing may be classified, whether it may bear an identity criterion, and whether it may ever appear in a subclass tree. The crucial contract: a Role is anti-rigid and is never a subclass of a Kind (it borrows identity from its bearer); a Kind is rigid and carries its own identity criterion.

Source: opda-classes.ttl (the UFO meta-classes opda:Role, opda:RoleMixin, opda:Relator) and each module's rdfs:comment / skos:scopeNote, which record the Guizzardi 2005 and DOLCE (Masolo et al. 2003) provenance per class.

Three-graph separation (ODR-0004 §3a)

The ontology keeps three artefacts strictly orthogonal — OWL classes ⊥ SHACL shapes ⊥ annotations — and the separation is CI-enforced. This is the single most load-bearing architectural decision (ODR-0004, Council session-004): it prevents open-world class semantics from being contaminated by closed-world cardinality, and keeps advisory hints out of the normative model.

Shapes target classes via sh:targetClass; they never owl:imports them. No property carries an OWL cardinality restriction and a SHACL count constraint as if the two were equivalent. Inference materialises into a fourth, derived graph (…/pdtf/graph/inferred/entailment) and never pollutes the canonical three. The CI gate asserts, among others, that an ASK over the annotation graph for any sh:-prefixed predicate returns false — no SHACL triples may leak into the annotation graph.

Six bounded contexts

The standard partitions the UK property industry into 6 primary bounded contexts (DDD), each a skos:Concept in opda:BoundedContextScheme and each owning a SHACL overlay profile (ODR-0020). PDTF is the Published Language between them. Domain-term membership in a context is a derived, on-demand query, never materialised — and upstream conformist authorities (HMLR, MHCLG, DSIT) own no overlay, so they are linked by opda:consumesFrom and are not members of the scheme.

Read live from opda-contexts.ttl (6 concepts in the scheme).

Inference / validation boundary (ODR-0029)

The governing principle (ODR-0029, Council session-039): infer the relations whose closure the author wants materialised (subclass / subproperty hierarchy, inverse, symmetric, transitive) — and validate the constraints the author wants checked (domain, range, cardinality, datatype, identity keys) as SHACL. domain / range sit on the validation side; RDFS only ever put them on the wrong side.

The entailment regime is understood as minimal / dormant: only rdfs:subClassOf type-propagation currently fires (0 triples on the schema, ~30 trivially recoverable on instance data); the other six rules are dormant carriers that activate when a real construct lands. The closure adds 0 triples over the flat schema — it is kept not for current output but as a governed boundary and negative consistency gate (no owl:sameAs, no spurious EPCCertificate ⊑ Property). The rule logic is frozen; the ruleset is a sound but RL-incomplete RDFS-Plus fragment (config/opda-rdfs-plus.rules), explicitly not an OWL 2 RL reasoner.

The 7 frozen rules — the "Safe Group" (ODR-0025 §R1)

Deliberately excluded (validated as SHACL, never inferred)

This is what makes the regime RL-safe rather than RL or DL: no identity merging, no equivalence, no domain/range classification, no restriction reasoning. The corresponding domain / range constraints are validated by the ~273 sh:targetSubjectsOf → sh:class SHACL shapes (ODR-0029 R3) — see SHACL shapes.

Related

The implicit-Property crux and the classification doctrine are on Identity & classification. Browse the terms these frames govern: Classes, Properties, Vocabularies (SKOS). The full reference index is the Ontology section overview.