The contacts that are probably one party are proposed

Status: accepted

Amended 2026-10-19 by 20261019140000: a pair by name weighs each word by how few contacts of the company carry it, reads every word of the name at any length, and counts what the longer name adds. The first rule proposed "LG SERVICES" and "ASBL UCM SERVICES" on one shared trade.

Context

merge_contacts() joins two contacts once somebody has said which two (0074). Books taken over in two passes leave dozens of such pairs among thousands of contacts — "Marlow Jane" and "Jane Marlow", "Dupont" and "Dupont Holdings", one supplier imported with its VAT number and again with its bank account — and nobody reads two thousand contacts side by side to find them.

The books already know how a party is recognised. A statement line and a ledger line that name nobody are weighed by contact_candidates() (0045, 0070): the account, the learned motifs, the significant words of a name, and a doubt when those words reach several contacts (0072). A second way of saying that two names agree would sooner or later disagree with the first.

Decision

suggest_duplicate_contacts(company) proposes the pairs, and decides nothing. One row per probable pair of active contacts of the company, strongest first:

It writes nothing. merge_contacts(keep_id, absorb_id) is still the act, and a person still chooses it.

The evidence is what the books recognise a party by.

• The same VAT number or the same registration number, compared once punctuation and case are set aside: 1.
• The same bank account, on the contact or in a learned motif (counterparty_account): 1, as contact_candidates() scores it.
• The words of the name, each weighed by how rare it is among the company's contacts: 1 over the number of contacts that carry it, so a word carried by one contact weighs 1 and a legal form carried by thirty weighs 1/30. Every word counts, at any length — the initials "LG", "KBC", "DKV" that tell two parties apart are shorter than the minimum length. For the shorter name and the longer, a pair needs the rarest significant word of the shorter (at the company's minimum length) in the longer, and what only one of them says — every word of the shorter missing from the longer, the significant words of the longer missing from the shorter — weighing no more than the significant words they share. The words of the longer below the minimum length are not counted against it: a name written in full grows by its legal form ("Isabel" and "ISABEL NV"). So one shared trade, place or legal form never makes a pair on its own: "LG SERVICES" is not "ASBL UCM SERVICES", "Parking" is not "Parking Cathédrale SA", and "Garage Annez" is "Garage Annez et fils". The same name is always a pair. No list of legal forms: the core has none, and the count catches the trade and the town as well. The score is the one contact_candidates() gives a name — 0.950 for the same name, 0.900 otherwise — capped at 0.600 when the shorter name agrees with several contacts, since it cannot say which one is the twin; the threshold is the company's name_threshold. contact_candidates() is not changed by the weighing: a statement line and a ledger line are suggested as before.

One scoring path. The score of a name and its cap move out of contact_candidates() into name_agreement() and name_among_several(), which contact_candidates() now calls, as suggest_duplicate_contacts() does. How a bank account is compared moves into account_key(), and how a VAT or registration number is compared into party_identifier(), which merge_contacts() now reads to refuse different_identifiers. A pair the merge would refuse is therefore never proposed.

Never proposed: a pair across two companies; an inactive or merged contact; a contact and its own parent or branch, which are linked on purpose; two contacts carrying different VAT or registration numbers. A merged pair disappears at the next call, and the kept contact is proposed again with any third contact it still resembles.

Bounded by construction. The pairs of a name are found through the rarest significant word of each name, which a pair needs in the other — never by comparing every contact with every other; identifiers are joined on their value. The function plans its joins as hash joins whatever the statistics say. At 2 000 contacts on PGlite it answers in about 40 ms.

Security invoker. It reads the contacts, motifs, lines and documents the caller may read; a company of somebody else gives no row.

Consequences

• A screen lists the pairs, shows the two contacts and the sentences, and calls merge_contacts() on the pair a person confirms.
• A statement line, a ledger line and a pair of contacts are scored by one rule; a change to how a name scores changes all three. Which pairs of contacts are compared at all is the duplicates' own: the weighing of the words reads two names, where a line reads one text.
• Contacts with the same name and nothing else to tell them apart are proposed. Many contacts sharing one exact name are many pairs; that is what the books say.

See also

• supabase/migrations/20261019104812_the_contacts_that_are_probably_one_party.sql
• supabase/migrations/20261019140000_a_pair_by_name_weighs_its_words.sql
• tests/duplicate_contacts.test.ts
• 0045 — A counterparty is recognised from learned patterns
• 0072 — A line may be left unnamed, and a name among several is a doubt
• 0074 — Two contacts of one company are merged, and the absorbed one is retired