# Create a Hierarchical Category Structure

The IDOL Category component provides a single category, the root category, which you cannot delete or modify. The root category serves as a base for the hierarchical category structure that you create. You can create categories under the root category:

- from scratch

- from clusters

- from legacy topic sets

- by copying categories

- by generating a taxonomy

- from XML

All categories are stored on disk, and become available for querying only if they are indexed into the IDOL category index (IDOL Agentstore component).

After you create categories, you can:

- train the categories

- retrain the categories

- move the categories

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