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//! Structural transformation from `snomed_owl::Axiom`s into the EL normal
//! forms (NF1–NF3, role hierarchy, role composition) `spec/13-classification.md`
//! defines.
use snomed_core::sctid::SctId;
use snomed_owl::{Axiom, ClassExpression, ObjectPropertyExpression};
use crate::skipped::SkippedConstruct;
use crate::types::{ConceptId, RoleId};
/// The normalized TBox, plus every concept/role id (named or fresh) that
/// needs a seeded entry in the completion state.
#[derive(Debug, Default)]
pub(crate) struct NormalizedTBox {
/// `A1 ⊓ ... ⊓ An ⊑ B` rules (NF1).
pub(crate) nf1: Vec<(Vec<ConceptId>, ConceptId)>,
/// `A ⊑ ∃r.B` rules (NF2), as `(A, r, B)`.
pub(crate) nf2: Vec<(ConceptId, RoleId, ConceptId)>,
/// `∃r.A ⊑ B` rules (NF3), as `(r, A, B)`.
pub(crate) nf3: Vec<(RoleId, ConceptId, ConceptId)>,
/// `r ⊑ s` role hierarchy axioms.
pub(crate) role_hierarchy: Vec<(RoleId, RoleId)>,
/// `r ∘ s ⊑ t` role composition axioms.
pub(crate) role_composition: Vec<(RoleId, RoleId, RoleId)>,
/// Every concept id (named or fresh) that appeared anywhere — the
/// seed set for completion.
pub(crate) all_concepts: std::collections::HashSet<ConceptId>,
pub(crate) skipped: Vec<SkippedConstruct>,
}
struct Normalizer {
tbox: NormalizedTBox,
next_fresh_concept: u32,
next_fresh_role: u32,
}
pub(crate) fn normalize<'a>(axioms: impl IntoIterator<Item = &'a Axiom>) -> NormalizedTBox {
let mut n = Normalizer {
tbox: NormalizedTBox::default(),
next_fresh_concept: 0,
next_fresh_role: 0,
};
for axiom in axioms {
n.add_axiom(axiom);
}
n.tbox
}
impl Normalizer {
fn fresh_concept(&mut self) -> ConceptId {
let id = ConceptId::Fresh(self.next_fresh_concept);
self.next_fresh_concept += 1;
self.seed(id);
id
}
fn fresh_role(&mut self) -> RoleId {
let id = RoleId::Fresh(self.next_fresh_role);
self.next_fresh_role += 1;
id
}
fn seed(&mut self, id: ConceptId) {
self.tbox.all_concepts.insert(id);
}
fn named(&mut self, id: SctId) -> ConceptId {
let c = ConceptId::Named(id);
self.seed(c);
c
}
fn add_axiom(&mut self, axiom: &Axiom) {
match axiom {
Axiom::SubClassOf { sub, sup } => self.add_subclass_of(sub, sup),
Axiom::EquivalentClasses(ops) => {
// A cycle of pairwise SubClassOf axioms is sufficient for
// full mutual subsumption — the completion algorithm's
// own transitive rule-firing does the rest (spec/13).
for i in 0..ops.len() {
let j = (i + 1) % ops.len();
self.add_subclass_of(&ops[i], &ops[j]);
}
}
Axiom::SubObjectPropertyOf { sub, sup } => {
let target = RoleId::Named(*sup);
match sub {
ObjectPropertyExpression::Named(r) => {
self.tbox.role_hierarchy.push((RoleId::Named(*r), target));
}
ObjectPropertyExpression::Chain(ids) => self.add_role_chain(ids, target),
}
}
Axiom::SubDataPropertyOf { sub, .. } => {
self.tbox.skipped.push(SkippedConstruct::DataProperty(*sub));
}
Axiom::TransitiveObjectProperty(r) => {
let rid = RoleId::Named(*r);
self.tbox.role_composition.push((rid, rid, rid));
}
Axiom::ReflexiveObjectProperty(r) => {
self.tbox
.skipped
.push(SkippedConstruct::ReflexiveProperty(*r));
}
}
}
/// Folds an `ObjectPropertyChain` of any length into binary role
/// compositions, introducing fresh intermediate roles as needed
/// (length 2 — SNOMED's only observed real usage, spec/12 — needs
/// none).
///
/// `snomed-owl`'s parser rejects a chain with fewer than two operands,
/// but `Axiom` is a public type a caller can build by hand, so the
/// degenerate lengths are handled rather than left to panic
/// (spec/13 rule 1): one operand is exactly a role hierarchy axiom,
/// and zero operands say nothing at all and are reported as skipped.
fn add_role_chain(&mut self, ids: &[SctId], target: RoleId) {
match ids {
[] => {
if let RoleId::Named(t) = target {
self.tbox.skipped.push(SkippedConstruct::EmptyRoleChain(t));
}
}
[only] => {
self.tbox
.role_hierarchy
.push((RoleId::Named(*only), target));
}
[first, middle @ .., last] => {
let mut acc = RoleId::Named(*first);
for &next in middle {
let fresh = self.fresh_role();
self.tbox
.role_composition
.push((acc, RoleId::Named(next), fresh));
acc = fresh;
}
self.tbox
.role_composition
.push((acc, RoleId::Named(*last), target));
}
}
}
fn add_subclass_of(&mut self, sub: &ClassExpression, sup: &ClassExpression) {
let conjuncts = self.normalize_conjuncts(sub);
if conjuncts.is_empty() {
return; // sub contributed nothing classifiable (spec/13 scope)
}
self.emit_subsumption(&conjuncts, sup);
}
/// Flattens a top-level `ObjectIntersectionOf` into its conjunct
/// concept ids (recursively normalizing each operand); any other
/// expression normalizes to a single-element list.
fn normalize_conjuncts(&mut self, expr: &ClassExpression) -> Vec<ConceptId> {
match expr {
ClassExpression::ObjectIntersectionOf(ops) => ops
.iter()
.filter_map(|op| self.normalize_conjunct_operand(op))
.collect(),
other => match self.normalize_conjunct_operand(other) {
Some(id) => vec![id],
None => vec![],
},
}
}
/// `None` for a `DataHasValue` operand (dropped per spec/13 scope,
/// and reported in `skipped`); otherwise the operand's concept id.
fn normalize_conjunct_operand(&mut self, expr: &ClassExpression) -> Option<ConceptId> {
match expr {
ClassExpression::DataHasValue { attribute, .. } => {
self.tbox.skipped.push(SkippedConstruct::ConcreteValue {
attribute: *attribute,
});
None
}
other => Some(self.normalize_concept_to_id(other)),
}
}
/// Converts any class expression into a single concept id, defining
/// a fresh name equivalent to it (in both directions) when it isn't
/// already a plain concept reference.
fn normalize_concept_to_id(&mut self, expr: &ClassExpression) -> ConceptId {
match expr {
ClassExpression::Concept(id) => self.named(*id),
ClassExpression::ObjectIntersectionOf(ops) => {
let conjuncts: Vec<ConceptId> = ops
.iter()
.filter_map(|op| self.normalize_conjunct_operand(op))
.collect();
match conjuncts.as_slice() {
[] => self.fresh_concept(), // every operand was DataHasValue
[single] => *single,
_ => {
let fresh = self.fresh_concept();
self.tbox.nf1.push((conjuncts.clone(), fresh)); // conjunction ⊑ F
for c in conjuncts {
self.tbox.nf1.push((vec![fresh], c)); // F ⊑ each conjunct
}
fresh
}
}
}
ClassExpression::ObjectSomeValuesFrom { attribute, filler } => {
let filler_id = self.normalize_concept_to_id(filler);
let fresh = self.fresh_concept();
let role = RoleId::Named(*attribute);
self.tbox.nf2.push((fresh, role, filler_id)); // F ⊑ ∃r.D
self.tbox.nf3.push((role, filler_id, fresh)); // ∃r.D ⊑ F
fresh
}
ClassExpression::DataHasValue { attribute, .. } => {
self.tbox.skipped.push(SkippedConstruct::ConcreteValue {
attribute: *attribute,
});
self.fresh_concept() // isolated atom: matches/is matched by nothing
}
}
}
/// Distributes `sup` (a class expression appearing on the right of a
/// `SubClassOf`, or reached recursively while distributing a
/// top-level intersection) into NF1/NF2 rules keyed by `conjuncts`.
fn emit_subsumption(&mut self, conjuncts: &[ConceptId], sup: &ClassExpression) {
match sup {
ClassExpression::Concept(id) => {
let target = self.named(*id);
self.tbox.nf1.push((conjuncts.to_vec(), target));
}
ClassExpression::ObjectIntersectionOf(ops) => {
for op in ops {
self.emit_subsumption(conjuncts, op);
}
}
ClassExpression::ObjectSomeValuesFrom { attribute, filler } => {
let filler_id = self.normalize_concept_to_id(filler);
let role = RoleId::Named(*attribute);
let source = match conjuncts {
[single] => *single,
_ => {
// Multiple conjuncts on the left, existential on
// the right: NF2 needs a single source concept,
// so introduce one standing for "all conjuncts
// hold". Only the conjunction -> fresh direction
// is needed here (nothing needs to derive the
// conjuncts back out of this particular fresh
// name).
let fresh = self.fresh_concept();
self.tbox.nf1.push((conjuncts.to_vec(), fresh));
fresh
}
};
self.tbox.nf2.push((source, role, filler_id));
}
ClassExpression::DataHasValue { attribute, .. } => {
self.tbox.skipped.push(SkippedConstruct::ConcreteValue {
attribute: *attribute,
});
}
}
}
}