You find a column named EntityNum in a table you manage, but what data belongs in this column? Not every detail of usage is clear from just SQL data type and constraints. What is the sensible range of values? Unit of measure? How is the column used by applications? Who in the world knows? We need a way to add comments to the database schema, just as we would write comments in application code to document how programmers should use it. But comments are useful only if they're correct and current, and if they're easy to read and to update. Schemadoc is an experimental tool to help in these goals.