XML and "Federated" Data

Chris Maden crism at oreilly.com
Fri Aug 6 17:20:23 BST 1999

[John Martin]
> Data Element/Attribute Name:  Zip Code
> Element Definition: As defined by USPS: The address element that
> identifies a geographic region or specific location defined by the
> postal service within the US.
> Valid values: USPS Table
> Element Format: 5N
> Element Length: 5 Bytes
> Element Type: Numeric

What about 9- or 14-digit zip codes?  What about foreign customers
with their own postal code notations?

I think a better approach is to define a "postal code" element or
attribute, and use application validation to check for a number of
possible legal values; for US addresses, it must be 5, 5-4, or 5-9 (I
think) syntax; for Britain and Canada, I believe the syntax is 3 3
with numbers or letters (9X9 X9X maybe?).  You could also, if they're
few enough, just not attempt to automate validation of non-US postal

The federation effort is going to be as difficult, or more so, than
any other document or database analysis effort.  Don't get in the way
of future expansion.  (A friend working on a prison database system
tells me they have six values for gender.)  That goes two ways: if you
start with a tight definition, you can loosen it later and old
documents still comply.  But if the validation is done in software,
then newer documents may be rejected by older systems; if that's what
you want, then that's fine, but it may be better to start loose and
tighten down later.

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