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From Apache Wiki <wikidi...@apache.org>
Subject [Db-derby Wiki] Update of "DataTypeDescriptor" by BryanPendleton
Date Thu, 19 Apr 2007 15:19:52 GMT
Dear Wiki user,

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The following page has been changed by BryanPendleton:
http://wiki.apache.org/db-derby/DataTypeDescriptor

The comment on the change is:
capture some notes from Dan

New page:
Ignoring the "compiler" aspect for the moment there are two components to a DataTypeDescriptor,
the underlying SQL type (INTEGER, CHAR, VARCHAR, XML etc.) represented as TypeId and attributes
of the descriptor (nullablity, length, precision, scale and now collation).

Thus

 DTD = TypeId + {attributes}

Some functionality is applicable to a type regardless of a specific DTD's attributes, thus
methods for that functionality can be declared on TypeId instead of DTD.

Some functionality on the other hand needs the attribute information as well, say the display
length of a type is a function of its length/precision&scale and its underlying SQL type.

The collation changes have moved the comparable check from being only reliant on the SQL type
(TypeId) to being dependent on the type's attributes (collation type and implicit/explicit).
Thus the original location for the comparable method made sense, but now does not. 

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