Rules stored as data | ESSA rule the system stores as rows is the system's to evaluate; the specification types its parts, injects its verdict and folds stored results with a row-set guard.ESShow-toesshow-toadopterdevelopertry-spec-driven-developmentspecify

Rules stored as data

A rule stored as data is evaluated by the system

Some systems store their rules as rows, written at run time: a condition's expression, operator and expectation, and a fold of ALL or ANY. ESS does not evaluate such a rule. The specification states the rule's parts as typed rows and leaves the verdict to the system's evaluator, as an external: outcome the suite injects:

format: ess/16
system: demo
version: v1
domain: demo.rules
summary: Conditions stored as rows; whether a rule holds is the evaluator's decision.
types:
  - {name: demo.rules.ConditionId, kind: newtype, of: Uuid}
  - {name: demo.rules.RuleId, kind: newtype, of: Uuid}
  - {name: demo.rules.Operator, kind: enum, variants: [Equals, GreaterThan, Matches]}
  - {name: demo.rules.Fold, kind: enum, variants: [All, Any]}
entities:
  - name: demo.rules.Condition
    identity: {name: condition_id, type: demo.rules.ConditionId}
    fields:
      - {name: rule_id, type: demo.rules.RuleId}
      - {name: expression, type: String}
      - {name: operator, type: demo.rules.Operator}
      - {name: expectation, type: String}
      - {name: fold, type: demo.rules.Fold}
    lifecycle: {initial: Active, states: [Active], terminal: [Active]}
errors:
  - {name: demo.rules.RuleNotMet, fields: [{name: rule_id, type: demo.rules.RuleId}]}
events:
  - name: demo.rules.ConditionAdded
    fields: [{name: condition_id, type: demo.rules.ConditionId}]
  - name: demo.rules.RuleMet
    fields: [{name: rule_id, type: demo.rules.RuleId}]
commands:
  - name: demo.rules.AddCondition
    input:
      - {name: condition_id, type: demo.rules.ConditionId}
      - {name: rule_id, type: demo.rules.RuleId}
      - {name: expression, type: String}
      - {name: operator, type: demo.rules.Operator}
      - {name: expectation, type: String}
      - {name: fold, type: demo.rules.Fold}
    outcomes:
      - name: added
        creates: demo.rules.Condition
        instance: condition_id
        sets:
          rule_id: input.rule_id
          expression: input.expression
          operator: input.operator
          expectation: input.expectation
          fold: input.fold
        emits: [demo.rules.ConditionAdded]
        payload: {demo.rules.ConditionAdded: {condition_id: input.condition_id}}
  - name: demo.rules.TestRule
    input: [{name: rule_id, type: demo.rules.RuleId}]
    outcomes:
      - name: not-met
        external: the evaluator finds the rule's stored conditions do not hold
        error: demo.rules.RuleNotMet
      - name: met
        emits: [demo.rules.RuleMet]
        payload: {demo.rules.RuleMet: {rule_id: input.rule_id}}
components:
  - component: rules
    owns: {domains: [demo.rules]}
    accepts: {commands: [demo.rules.AddCondition, demo.rules.TestRule]}
    reached_by: network

The synthesized suite forces not-met and requires its error, and sends TestRule with no verdict forced for met. Where the system stores each condition's result as a row field, such as holds: Boolean, the ALL/ANY fold over those results is a fact the specification can state: from ess/22, a when_related row-set guard with forall or exists. The boundary, and why ESS does not interpret stored rules, is in the stored-rules design note.

A rule stored as data is evaluated by the system​

A rule stored as data is evaluated by the system