Skip to content

owl:imports behavior

How OntoLogos handles imported ontologies when loading files.

Summary

Aspect Behavior
Remote URLs Not fetched — http:// or https:// import IRIs are not downloaded over the network
RDF/XML (.owl, .rdf, .xml) Local imports merged when using load_ontology() (merge_imports: true); ParseLimits::default() has merge_imports: false
Turtle (.ttl, .turtle) Not merged — only axioms in the loaded file
OWL Functional (.ofn, .func) Not merged — only axioms in the loaded file
Transitive imports RDF/XML merge follows import chains for local files only (visited-set deduplication)

OntoLogos does not implement a full OWL catalog resolver. Import IRIs must map to files relative to the loaded document (or sandbox base directory).

Decision table: which loader?

I use… merge_imports default Local RDF/XML imports merged? When to set merge_imports: false
load_ontology(path) on RDF/XML true Yes Single-document load only
load_ontology(path) on Turtle / OFN n/a No —
load_ontology_with_limits(path, ParseLimits::default()) false No Set merge_imports: true explicitly for RDF/XML bundles
load_ontology_in(base, path) same as above Same rules Untrusted uploads — prefer false unless sibling imports are trusted

Common mistake

load_ontology() merges imports; ParseLimits::default() does not. If you switch to load_ontology_with_limits for size caps, set merge_imports explicitly.

RDF/XML: default merge

For RDF/XML loads, load_ontology merges declared owl:imports that resolve to local files:

use ontologos_parser::{load_ontology, load_ontology_with_limits, ParseLimits};

// load_ontology() opts in to merge_imports = true for RDF/XML
let ontology = load_ontology(path)?;

// Single-document load only (no import merge)
let limits = ParseLimits {
    merge_imports: false,
    ..ParseLimits::default()
};
let ontology = load_ontology_with_limits(path, limits)?;

Imported documents are loaded recursively, but nested import merge is disabled per import file (merge_imports: false on nested loads) to avoid duplicate expansion — the visited set prevents cycles.

When to merge upstream

Merge with external tooling when:

  • Imports use remote IRIs (not on disk next to the ontology)
  • You load Turtle or OWL Functional and need a multi-file bundle
  • You need Protégé-style catalog resolution across arbitrary paths

ROBOT example:

robot merge --input ontology.owl --output merged.owl

Then load merged.owl with OntoLogos.

Diagnostics

owl:imports declarations appear in parse_meta.constructs whether or not merge succeeds. Unresolvable imports do not fail the load — axioms from those imports are simply absent. Check parse_meta.warnings for skipped imports (e.g. axiom limit exceeded).