DefaultDbValue
Initial value used when evolving the database or creating the database.
This value should be in the format expected by the database engine. For example 0 or 1 for a boolean using SQL Server.
Should be 'stringvalue' for a string default value.
Initial value
Initial value used in-memory.
Should be true/false or nothing for null (if nullable) or other value depending on type of attribute.
Allow Null
Controls both the in-memory nullability and database attribute setting. If this is false, most database engines require a DefaultDbValue to evolve the database. If no value is provided, the existing rows (objects) in database will get an invalid value and the evolve will fail.