Feature Model, Tree, and Validation

This module serves the feature model, derives the tree and the default selection from it, and validates selections. Read it when you change a validation rule or the model response.

What the model endpoint returns

GET /api/feature-model returns everything the client needs to show and configure the model:

Field	Content
model	Id, name, version, and status of the model
features, relations, constraints	The model as it is stored
tree	The same features arranged as a tree
defaultSelectedFeatureIds	The starting selection
warnings	Model warnings, such as constraints the server cannot evaluate

The server sends both the flat lists and the tree, so the client never builds the tree itself.

Tree and default selection

FeatureModelTreeService builds the tree from the root and the relations. Children appear in the order of their relation, and each tree node carries the relation that connects it to its parent. The same order is used everywhere the server returns feature ids, so lists are stable.

The default selection is every selectable feature whose default state is enabled, in tree order. FeatureModelCatalogService computes it, and the Configurator starts from it.

Validating a selection

POST /api/feature-model/validate takes a list of feature ids and checks them against the loaded model:

curl -X POST http://localhost:8090/api/feature-model/validate \
  -H 'Content-Type: application/json' \
  -d '{"selectedFeatureIds": ["mysql", "postgresql"]}'

The answer says whether the selection is valid, returns the known ids in tree order as normalizedSelection, and lists violations and warnings. FeatureModelValidationService applies these rules:

Code	Rule
UNKNOWN_SELECTED_FEATURE	Every selected id exists in the model.
MANDATORY_FEATURE_MISSING	When a parent is active, its mandatory selectable children are selected. Root and group nodes always count as active.
ALTERNATIVE_GROUP_SELECTION_MISSING	An active alternative group has at least one selected child.
REQUIRES_CONSTRAINT_VIOLATED	A selected source of a requires constraint has its target selected.
EXCLUDES_CONSTRAINT_VIOLATED	The two features of an excludes constraint are not both selected.
UNSUPPORTED_EXPRESSION_CONSTRAINT	A warning: expression constraints are reported but not evaluated.

An alternative group allows at most one child because the model pairs it with excludes constraints, such as mysql excludes postgresql.

Every violation carries a message, the affected featureIds, and a suggestion such as "Enable 'modeling' or disable 'apollon'." The client shows these texts as they are, so a new rule needs no client change.

Model integrity

Before the model is used, FeatureModelIntegrityService checks that it is well formed: unique ids, exactly one root, relations and constraints that point to existing features, artifact mappings with a known source, and no two environment mappings that produce the same variable name. These checks also run at startup as part of loading the runtime bundle. A model that fails them never reaches a user.

Add a validation rule

1. Add a code to ValidationCode.
2. Add a small method to FeatureModelValidationService that returns violations for the rule, and call it from validationViolations.
3. Write a clear message and a suggestion that tells the user what to change.
4. Test the rule in FeatureModelValidationServiceTest with a synthetic model from TestFeatureModels.

Where it lives in the code

Path	Responsibility
catalog/service/FeatureModelCatalogService	Builds the model response and the default selection
catalog/service/FeatureModelIntegrityService	Checks that the model is well formed
catalog/repository/FeatureModelStore	Gives services the loaded model
visualization/service/FeatureModelTreeService	Builds the tree and the tree order
validation/service/FeatureModelValidationService	Validates a selection
validation/domain/ValidationCode	All integrity and validation codes

Paths are relative to src/main/java/de/tum/cit/aet/artemis/featuremodel/.