At the moment Oracle database allows developers to add a single Comment to tables, views, columns, as well as a handful of other object types.
SQL Server supports the concept of "Extended Properties" which allow unlimited name/value pairs to be added to almost any schema object including:
- Database (== Oracle schema, I believe)
- Stored Procedures
- User-defined Functions
- Table
- Table Column
- Table Index
- Views
- Rules
- Triggers
- Constraints
https://www.mssqltips.com/sqlservertip/5384/working-with-sql-server-extended-properties/
"Extended Properties can be used to:
- Specify a caption for a table, view, or column.
- Specify a display mask for a column.
- Display a format of a column, define edit mask for a date column, define number of decimals, etc.
- Specify formatting rules for displaying the data in a column.
- Describe a specific database objects for all users."
I can think of other uses for this sort of thing as well, primarily to do with systematic markup of attributes to be used for automated code generation.
Of course, one could create a table and an API package to build something like this, and you'd then need a DDL trigger to detect dropped objects, etc. but it would be great to have this available as a builtin feature of the database.