Relationship Constraints Reference

Pair-Wise Constraints

Constraints restrict which element types a relationship type can connect. They are defined as a list of valid pairs — each specifying a source element type and a target element type.

Constraint structure

"constraints": {
  "validPairs": [
    { "source": "application-component", "target": "application-service" },
    { "source": "application-component", "target": "application-component" }
  ]
}

Each pair references element types by their $id.

Enforcement

• When drawing a relationship on the Canvas, only valid source/target pairs are allowed
• The relationship type picker only shows types that have a valid pair for the selected source and target
• Invalid attempts are silently prevented — no relationship is created

Editing constraints

A relationship type’s constraints are edited as a grid in the Constraints section of its Properties: rows are sources, columns are targets. Changes to the grid are held until you click Save; Discard puts it back. See How to create a relationship type.

Unconstrained Relationships

A relationship type with no constraints (empty validPairs or omitted constraints) can connect any two elements. This is useful for general-purpose relationships like Association.

"constraints": {}

Wildcard Constraints

Some built-in relationship types use "*" as a wildcard for one end:

{ "source": "note", "target": "*" }

This means the source must be a Note, but the target can be any element type.

Constraint Validation

The integrity checker can detect M1 relationships that violate their M2 type’s constraints. This can happen when:

• An M2 constraint is added or tightened after M1 relationships were already created
• A .farki file is imported with relationships that don’t match the available M2 constraints

Violations are reported as warnings — existing relationships are not automatically deleted.