Is your feature request related to a problem? Please describe.

We need a way to describe schemas of a dataset.

Describe the solution you'd like

Describe schemas in the DSL:

schema MySchema {
    "column name": ColumnType
}

Here, we can refer to MySchema from other places of the program and the data types of the attributes can refer to other classes.

Describe alternatives you've considered

Describe schemas as JSON. Overall, it's the inferior solution since we can provide less support. This is particularly an issue if the user writes the schema by hand.