a default value (not specified) exists for the value
value can be set to NULL (in the SQL sense)
the value is not valid (with regards to the context)
the value can be resetted to its "original" value (i.e. before it was modified)
value is defined as the default value (the value itself is not specified)
value is NULL (in the SQL sense)
the value has not been changed (in the context of the attribute usage)
no specific attribute
the value can't be modified
Attributes of a value, used internally by Libgda in different contexts. Values can be OR'ed.