Re: [Wikidata] Stable Interface Policy: Database Schema as a stable API

Hi all! I plan to add the wikibase (SQL) database schema as a stable interface. Typically, a database schema is considered internal, but since we have tools on labs that may rely on the current schema, breaking changes to the schema should be announced as such. To address this, I plan to add the following paragraph to the Stable Public APIs section: The database schema as exposed on Wikimedia Labs is considered a stable interface. Changes to the available tables and fields are subject to the above notification policy. In addition, I plan to add the following paragraph to the Extensibility section: In a tabular data representation, such as a relational database schema, the addition of fields is not considered a breaking change. Any change to the interpretation of a field, as well as the removal of fields, are considered breaking. Changes to existing unique indexes or primary keys are breaking changes; changes to other indexes as well as the addition of new unique indexes are not breaking changes. If you have any thoughts ob objections, please let me know at <https://www.wikidata.org/wiki/Wikidata_talk:Stable_Interface_Policy#Database_Schema_as_a_stable_API>