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Inheritance

K-types support single and multiple inheritance through the extends field. A child k-type IS-A instance of its parent and inherits its definitions.

Basic usage

# k-types/characterization-process/specs/k-type.spec.yaml
id: characterization-process
extends: ../process/specs/k-type.spec.yaml
# k-types/tensile-test/specs/k-type.spec.yaml
id: tensile-test
extends: ../characterization-process/specs/k-type.spec.yaml

This creates a chain: tensile-test IS-A characterization-process IS-A process.

What is inherited

Field Merge behaviour
ontology_classes Appended; child is an instance of all parent classes
semantic_schemas Merged by id; child adds entries or overrides a version
relations Merged by id; child inherits all parent relations
custom_properties sections Merged by section id; child adds sections or adds inputs to existing ones
tags Appended
kv_properties Inherited as-is; child overrides individual keys

Narrowing vs. widening: a child can make a field more restrictive (e.g. make a required: false relation required: true) but cannot relax a parent's constraint.

Multiple inheritance

A k-type can extend more than one parent:

extends:
  - ../manufacturing-process/specs/k-type.spec.yaml
  - ../material-forming/specs/k-type.spec.yaml

Merge order: parents are resolved left-to-right, with later entries taking precedence over earlier ones. The child's own definitions override everything. This is analogous to Python's MRO for linear chains.

If two parents declare a relation with the same id, the last parent's definition wins, then the child's definition overrides that.

extends resolution

During local development, use a relative path:

extends: ../process/specs/k-type.spec.yaml

At publish time, tooling replaces relative paths with the parent's $id (a pinned GitHub URL), making the published spec fully self-contained:

extends: "https://github.com/semantic-dataspace/knowledge-types/blob/v0.1.0/k-types/process/specs/k-type.spec.yaml"

Both forms are valid in the repository at all times.

Cycle detection

A k-type must not extend itself directly or indirectly. Tooling walks the extends chain and raises an error if the same $id is encountered twice. Authoring tools should validate this before accepting a pull request.

Practical example: tensile-test

tensile-test declares no relations of its own, but inherits three from characterization-process:

Relation id From Target k-type Ontology property
has_operator characterization-process expert prov:wasAssociatedWith
uses_instrument characterization-process measurement-device schema:instrument
has_specimen characterization-process specimen PMDCo property

And its effective ontology_classes are:

Class Source
pmdco:Process process (grandparent)
obi:Assay characterization-process (parent)
tto:TensileTest tensile-test (self)
SteelPO:TensileTest tensile-test (self)

The child only needs to declare the delta; the rest propagates automatically.