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This is a Java API that presents a number of DDL type operations, however it is not as comprehensive as the Metastore API. The HCatClient was intended to the Java based the entry point to WebHCat HCatalog API although this was never realised. Currently HCatClientHMSImpl is the only concrete implementation of the API; it integrates directly with the Metastore using the Metastore API and does not utilise WebHCat whatsoever despite being packaged inside the WebHCat project. The HCatClientHMSImpl was originally provided as a reference implementation but it has over time gained traction a public client. Anecdotally, it is now the officially preferred API for issuing DDL type operations from external programs and feature contributions are encouraged. There is some minimal documentation on the wiki in the form of a design document describing the interface but not the implementation.

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