The knowledge layer

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The knowledge layer is powered by ex_datalog. It contains business facts, accounting facts, event facts, entity facts, account facts, relationship facts, policy facts, template facts, mapping facts, and constraint facts.

What the knowledge layer answers

  • Should this event be processed?
  • Is this event blocked?
  • Does this event require approval?
  • Which accounting policy applies?
  • Which posting template applies?
  • Which debit/credit account should be used?
  • Which dimensions are required?
  • Which account mapping applies?
  • Which warnings should be attached?

The important rule

Datalog should not construct Elixir structs. Datalog decides facts and relationships. Elixir materializes journals, postings, and persisted records.

Program

Logistiki.Knowledge.Program is an ExDatalog.Schema that declares:

  • Relations for per-event runtime facts (event_type, event_amount_cents, event_account, event_cash_account, event_fee_income_account, ...).
  • Relations for derived business rules (blocked, requires_approval).
  • Relations for accounting policy selection (policy).
  • Relations for posting templates and account roles (template, template_posting, requires_dimension, account_role_static, account_role).
  • Static facts for templates, template postings, required dimensions, and static account mappings.
  • Rules that derive blocked, requires_approval, policy, and account_role from the per-event facts.

Runtime facts

Logistiki.Knowledge.Facts.generate/1 builds a list of {relation, values} facts from a Logistiki.Event.Normalized event. The event is represented by the fixed atom :evt inside the Datalog program. Logistiki.Knowledge.KnowledgeBase loads Program.program/0 (which includes the compile-time static facts), adds the runtime facts via ExDatalog.Program.add_fact/3, materializes the knowledge, and interprets the result into a Logistiki.Knowledge.Result.

Result

Logistiki.Knowledge.Result captures:

  • blocked, requires_approval
  • policy — the selected accounting policy atom
  • template — the selected template (= the policy in v0.1.0)
  • template_postings — ordered posting specs
  • account_roles — role => account_code
  • required_dimensions
  • explanation

Public API

Logistiki.Knowledge.evaluate(normalized_event)
Logistiki.Knowledge.materialize(normalized_event)
Logistiki.Knowledge.load_program()
Logistiki.Knowledge.assert_fact(predicate, arguments)

Logistiki.Knowledge.PolicySelector and Logistiki.Knowledge.TemplateResolver are thin façades for callers that only need the policy or template decision.