I see the line of thinking you're going down. There are ISO standards for data types, in a sense I could see why one would seek a standard language for defining the metadata/specification of a type as data. Have to really think about that some more.. in a way a regex could be seen as a compact form of expressing the capability of a column in terms of value ranges or domains, but to define the meaning of the data, not so much.
Your interpretation of the atomic columns requirement is a little different than my understanding. That requirement of normalization only applies to the "cells" of columnar data, it says nothing about encoding meaning into column names, which are themselves simply descriptive metadata.
I mean, for sure you wouldn't want to encode many values/meanings into a column name (some systems have length restrictions that would make that impossible, I'm not sure it makes sense anyway), but just pointing out that technically the spec does not make that illegal. Certainly, adding minor annotations within the name of a column separated by a supported delimiter does not, in my opinion, violate normalization rules at all. I mean things like "ID_" or similar.
Have you looked at INFORMATION_SCHEMA in SQL databases? [1] You mentioned SQL metadata and constraints, that is as close to a standard feature for querying that information there is, some databases do it using similar but non-standard ways (Oracle for example).
Also, not standard but, many relational databases support extended properties or Metadata for objects (tables, views, columns, etc.) - you can often come up with your own scheme although rarely do I see people utilize these features. [2] [3]
At some point it feels like we are more talking about type definitions and annotations, applied to data columns.
Maybe like, BNF [4] for purely data table columns (which are essentially types)?
Your interpretation of the atomic columns requirement is a little different than my understanding. That requirement of normalization only applies to the "cells" of columnar data, it says nothing about encoding meaning into column names, which are themselves simply descriptive metadata.
I mean, for sure you wouldn't want to encode many values/meanings into a column name (some systems have length restrictions that would make that impossible, I'm not sure it makes sense anyway), but just pointing out that technically the spec does not make that illegal. Certainly, adding minor annotations within the name of a column separated by a supported delimiter does not, in my opinion, violate normalization rules at all. I mean things like "ID_" or similar.
Have you looked at INFORMATION_SCHEMA in SQL databases? [1] You mentioned SQL metadata and constraints, that is as close to a standard feature for querying that information there is, some databases do it using similar but non-standard ways (Oracle for example).
Also, not standard but, many relational databases support extended properties or Metadata for objects (tables, views, columns, etc.) - you can often come up with your own scheme although rarely do I see people utilize these features. [2] [3]
At some point it feels like we are more talking about type definitions and annotations, applied to data columns.
Maybe like, BNF [4] for purely data table columns (which are essentially types)?
[1] https://en.wikipedia.org/wiki/Information_schema
[2] http://www.postgresql.org/docs/current/static/sql-comment.ht...
[3] https://docs.microsoft.com/en-us/sql/relational-databases/sy...
[4] https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form