Transaction module — relational schema

transaction is a reified UFO Relator — the conveyancing relationship that founds the buyer and seller roles and concerns one or more legal estates. milestone rows are append-only lifecycle events; transaction_chain aggregates linked transactions.

Tables

Table	Realises	Kind	Key relationships
`transaction`	Transaction	relator	founds `seller` / `buyer`; FK → `transaction_chain` (`0..1`)
`transaction_legal_estate`	concerns `M:N`	junction	`transaction` × `legal_estate`
`milestone`	Milestone	event	FK → `transaction`; `UNIQUE(transaction_id, milestone_kind)`
`transaction_chain`	TransactionChain	aggregate	members via `transaction.transaction_chain_id`

Entity-relationship diagram

erDiagram accTitle: Transaction module — entity-relationship diagram accDescr: transaction as a reified relator with milestones, concerning legal estates via a junction, positioned in a transaction_chain. The buyer and seller roles it founds live in the agent module. transaction { uuid transaction_id PK text uri UK timestamptz occurred_at_time uuid transaction_chain_id FK } transaction_legal_estate { uuid transaction_id PK,FK uuid legal_estate_id PK,FK } milestone { uuid milestone_id PK text uri UK uuid transaction_id FK text milestone_kind FK timestamptz occurred_at_time timestamptz planned_at_time } transaction_chain { uuid transaction_chain_id PK text uri UK } transaction_chain ||--o{ transaction : "chain members" transaction ||--o{ milestone : "has milestone" transaction ||--o{ transaction_legal_estate : "concerns" legal_estate ||--o{ transaction_legal_estate : "concerned by"

Lookup tables

Lookup	Bound by	Members
`milestone_kind`	`milestone.milestone_kind`	5
`transaction_status`	overlay profiles	5

Mapping notes

Transaction is a reified Relator, not a pair of foreign keys. Its identity is the 5-tuple (LegalEstate-concerned, Sellers, Buyers, transaction-id lineage, founding event). Buyers and sellers attach as seller / buyer rows (agent module) whose transaction_id points back here; concerns is many-to-many via transaction_legal_estate.
milestone identity is (Transaction, MilestoneKind) — UNIQUE(transaction_id, milestone_kind). The derived hasVarianceDays (occurred_at_time − planned_at_time) is computed, not stored.
The ≤ 7 chain-member cap and chain-status are overlay-level SHACL rules, documented rather than enforced as base-table constraints. Membership is the inverse foreign key transaction.transaction_chain_id. (legal_estate lives in the property module.)

Cross-tier

Logical tier: transaction module.