Hi,
If you are developing with Atlassian Connect, there are no predefined standards specifically for databases. There are some security requirements, and if you want to get a Cloud Security or Cloud Fortified badge there are some additional operational requirements that you will need meet in order to qualify for these programs. Perhaps the part about databases & security in this post helps: How Can I Deploy My Cloud App to PROD - #2 by remie
If you are developing with Forge, the Forge Storage API is available for key/value storage fo data.