Federation: when standpoints disagree

Area: Standpoints & federation Teaches: across [...] joins standpoints by the four-valued information-join (FDE / Truth4). When two sources speak to the same individual, the join surfaces all four values — is, not, can, and crucially both, which arises only from one source asserting while another refutes. Prerequisites: standpoint visibility (DEFAULT vs scoped facts). Run: ox build examples/federation_disagreement && ox query examples/federation_disagreement --with-truth4

Two data sources rarely agree on everything. Most systems force you to pick a winner or crash on the conflict. Argon does neither: it federates them and reports the disagreement as a value. The four-valued truth space — is (asserted), not (refuted), can (neither), both (asserted and refuted) — is a bilattice, and across [...] combines standpoints by the information-join over it. A conflict does not corrupt the answer; it becomes both.

What to read in federation.ar

Two standpoints, each its own source of truth:

pub type Person;

pub standpoint historical;
pub standpoint public_record;

One source asserts with fact; the other refutes with not_fact (strong negation):

pub standpoint historical {
    pub fact Person(alice);
    pub fact Person(bob);
}

pub standpoint public_record {
    pub not_fact Person(alice);
    pub not_fact Person(carol);
    pub fact Person(dave);
}

not_fact is not absence — it is a positive refutation. historical says alice is a Person; public_record says alice is not. They overlap on alice and clash.

The federated query joins both sources:

pub query everyone() -> Person across [historical, public_record];

Running it

The query returns one row per individual, each tagged with the joined four-valued status:

alice  → Both   (historical asserts Person, public_record refutes)
bob    → Is     (only historical asserts)
carol  → Not    (only public_record refutes)
dave   → Is     (only public_record asserts)

All four Truth4 values appear in a single query. The decisive row is alice → Both: she is the only individual both asserted (by historical) and refuted (by public_record), and the information-join carries both polarities rather than discarding either. bob and dave are Is because exactly one source asserts and nothing refutes; carol is Not because she is refuted with no countervailing assertion. The can value is the join’s bottom — neither asserted nor refuted — and is what an individual no source mentions would read.

Honest caveats (what runs today)

• This is the default paraconsistent federation policy: a conflict is preserved as Both rather than resolved or rejected. A source declaring a contradiction does not poison the whole query.
• Rows are reported by individual id; the name mapping above is how the package declares its facts.

This example is compiled and run in CI; the per-row Truth4 verdicts under federation are pinned by a corpus test (oxc-runtime/tests/examples_corpus.rs), so the information-join can’t drift from the language.