# fiftyone.core.annotation.hydrate_label_schemas Annotation label schema hydration Resolves `applied_ontology` references in label schemas by merging the referenced annotation ontology’s attributes into the schema’s `attributes` list, tagging merged attributes with a `_source` marker. Copyright 2017-2026, Voxel51, Inc.
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**Functions:** | [`attributes_with_source`](#fiftyone.core.annotation.hydrate_label_schemas.attributes_with_source)(ontology) | Returns ontology attributes as dicts tagged with a `_source` marker. | |------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------| | [`hydrate_applied_ontology`](#fiftyone.core.annotation.hydrate_label_schemas.hydrate_applied_ontology)(label_schema) | Merges a referenced annotation ontology's attributes into a label schema. | | [`dehydrate_applied_ontology`](#fiftyone.core.annotation.hydrate_label_schemas.dehydrate_applied_ontology)(label_schema) | Strips hydration artifacts from a label schema before it is saved. | | [`inline_applied_ontology`](#fiftyone.core.annotation.hydrate_label_schemas.inline_applied_ontology)(label_schema, ontology) | Permanently inlines an annotation ontology's attributes into a label schema as local copies and removes the `applied_ontology` reference. | ### fiftyone.core.annotation.hydrate_label_schemas.attributes_with_source(ontology: Any) → [list](fiftyone.core.session.events.md#fiftyone.core.session.events.Colorscale.list)[dict[str, Any]] Returns ontology attributes as dicts tagged with a `_source` marker. * **Parameters:** **ontology** – an ontology object whose `.attributes` are attribute specs with a `.to_dict()` method and whose `.name` identifies the ontology * **Returns:** a list of attribute dicts, each carrying `_source: ontology.name` ### fiftyone.core.annotation.hydrate_label_schemas.hydrate_applied_ontology(label_schema: dict) → dict Merges a referenced annotation ontology’s attributes into a label schema. If `label_schema` has an `applied_ontology` key that resolves to an annotation ontology, returns a new dict with the ontology’s attributes merged into the `attributes` list. Each merged attribute carries a `_source: ` marker. Attributes are matched by `name` and ontology values win on collision. When the ontology has a bundled taxonomy, an `applied_taxonomy` key is also surfaced on the response; it is never persisted on the schema itself. If the schema has no `applied_ontology` reference, the schema is returned unchanged. If the reference is dangling (deleted ontology) or points at a non-annotation ontology, the `applied_ontology` key is stripped from the returned schema and a WARNING is logged. This lets a subsequent save silently persist a clean schema rather than failing validation on the dangling reference. * **Parameters:** **label_schema** – a label schema dict * **Returns:** a hydrated copy of `label_schema`, a copy with `applied_ontology` stripped if the reference is dangling, or the schema unchanged when there is nothing to do ### fiftyone.core.annotation.hydrate_label_schemas.dehydrate_applied_ontology(label_schema: dict) → dict Strips hydration artifacts from a label schema before it is saved. Companion to [`hydrate_applied_ontology()`](#fiftyone.core.annotation.hydrate_label_schemas.hydrate_applied_ontology). When the schema has an `applied_ontology` that resolves to an annotation ontology, drops any attribute whose `name` matches an ontology-owned attribute, strips the `_source` marker from the remaining attributes, and drops the `applied_taxonomy` key (surfaced at hydrate time, never persisted). Otherwise (no reference, dangling reference, or non-annotation reference) the schema is returned unchanged — the validator will surface the reference-level problem. * **Parameters:** **label_schema** – a label schema dict, possibly carrying hydration artifacts from [`hydrate_applied_ontology()`](#fiftyone.core.annotation.hydrate_label_schemas.hydrate_applied_ontology) * **Returns:** a deep-copied schema with hydration artifacts removed, or `label_schema` unchanged when there is nothing to dehydrate ### fiftyone.core.annotation.hydrate_label_schemas.inline_applied_ontology(label_schema: dict, ontology: Any) → dict Permanently inlines an annotation ontology’s attributes into a label schema as local copies and removes the `applied_ontology` reference. Used when the referenced ontology is about to be deleted (or for any other “freeze the current ontology state into the schema” operation). Unlike [`hydrate_applied_ontology()`](#fiftyone.core.annotation.hydrate_label_schemas.hydrate_applied_ontology), the merged attributes are NOT marked with `_source` — they are now first-class local attributes — and the `applied_ontology` key is stripped from the result. The caller is responsible for resolving the ontology; this function does not load anything. * **Parameters:** * **label_schema** – a label schema dict * **ontology** – an `AnnotationOntology` whose attributes should be inlined * **Returns:** a deep-copied schema with the ontology’s attributes merged in as locals and the `applied_ontology` reference removed