# `Logistiki.Knowledge.Rules`
[🔗](https://github.com/thanos/logistiki/blob/v0.1.0/lib/logistiki/knowledge/rules.ex#L1)

Documentation and helpers for the three rule categories in Logistiki.

## Business rules (Datalog-backed)

Answer: should this event be processed? Is it blocked? Is approval needed?
Is compliance review needed? Is it operationally allowed?

Implemented as Datalog rules in `Logistiki.Knowledge.Program` (`blocked`,
`requires_approval`).

## Accounting policies (Datalog-backed)

Answer: which accounting policy applies? Which posting template applies?
Which account roles are used? Which dimensions are required? Which valuation
method applies?

Implemented as Datalog rules (`policy`) and facts (`template`,
`template_posting`, `requires_dimension`, `account_role_static`).

## Ledger invariants (pure Elixir)

Answer: what must *always* be true? Implemented in
`Logistiki.Accounting.InvariantValidator`. These must never depend on Datalog.

Datalog may say what should happen. Elixir enforces what must always be true.

# `categories`
*since 0.1.0* 

```elixir
@spec categories() :: keyword()
```

Returns the rule categories with descriptions.

## Returns

  * `keyword()` — a keyword list of `category_atom => description_string`.

## Examples

    iex> Logistiki.Knowledge.Rules.categories()
    [
      business_rules: "Datalog-backed: should the event be processed / blocked / approved?",
      accounting_policies: "Datalog-backed: which policy, template, roles, dimensions apply?",
      ledger_invariants: "Pure Elixir: debits equal credits, postings positive, immutable, etc."
    ]

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*Consult [api-reference.md](api-reference.md) for complete listing*