The “base” name appears to be misleading. I assumed this feature would add a structured data format to Obsidian, but it does not. This is exclusively a query engine for your existing markdown files.

An obsidian base is primarily defined as a code block in an existing markdown file. That code block defines a series of queries (filters, really) that produce a result set of markdown file names.

So… more a way to work with a large collection of markdown files than a relational database.