User Defined Data Types

I have reviewed every book I have, tahiti (I'd rather wish it had been the island), asktom, etc. and can find not a single example of something so I'm tossing it out to the community at large.

I can create user defined data types and attach methods ... well documented and quite simple.

But what I can't seem to do is mimic the ability of Oracle's date data type to only accept dates and number data type (for example NUMBER(5,2)) to constraint what it accepts. What I'd like is some way to create something like a social security number data type that would only accept entiries in the format 999-99-9999 without writing an independent constraint.

Any thoughts? Any examples? Thanks.

-- 
Daniel Morgan
http://www.outreach.washington.edu/ext/certificates/oad/oad_crs.asp
http://www.outreach.washington.edu/ext/certificates/aoa/aoa_crs.asp
damorgan_at_x.washington.edu
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