XML Catalogs demystified

The XML catalog is a file that tells tools like robot and Protégé where to find locally-stored OWL files when processing imports. It is a relatively simple, but important, piece of infrastructure that is vital for managing ontology imports.

Here is a sample line from an XML catalog:

<uri name="https://w3id.org/elmo/elmo/imports/ro_import.owl" uri="imports/ro_import.owl"/>

This tells the tool that if it sees the URI https://w3id.org/elmo/elmo/imports/ro_import.owl, replace that with imports/ro_import.owl which will access the local file. It is essentially redirecting internal requests from https://w3id.org/elmo/elmo/imports/ro_import.owl to the local file.

An XML catalog is used in the ODK to manage imports so that the tool does not have to constantly re-download imported ontologies.

Here are some additional resources about XML catalogs:

• robot XML Catalogs documentation
• Protégé and XML Catalogs