[HAPI-devel] new validation model

[Tripp, B. <Bry...@uh...>]

Hi Everyone, 

I've been speaking with Alan Shields and Neal Acharya about a new validation
model for HAPI.  This seems like a good candidate for a new sub-project, so
if anyone is interested in working on this please let us know.  

Currently, the only run-time message validation HAPI performs is within the
setValue() methods of the Primitive datatype classes.  For example when you
call setValue() on a DT an exception is thrown if the String arg is not in
the correct DT format.  This has served pretty well so far but it leaves us
with the following limitations: 

1. Sometimes validation is inappropriate.  This is the problem Alan ran into
-- the TN class was rejecting his perfectly valid UK telephone numbers
because they didn't conform to the North American format.  
2. Can't add further optional constraints (such as all timestamps must have
a time zone).  
3. Can't turn off validation to improve performance. 
3. Other forms of validation (e.g. conformance profiles, standard DTDs) are
not covered.  

We're considering expanding run-time validation and making it configurable.
In a nutshell, the idea is to implement each validation rule as a Rule
object with a test() method that could be invoked or not, depending on
run-time configuration.  Three types of rules seem appropriate: 

1. DataTypeRule: Called when the values of simple datatypes are set, like
the existing hard-coded datatype validations (e.g.
TNFollowsNorthAmericanFormat).  
2. MessageRule: Called when complete message content is to be checked on a
parsed message (e.g. conformance profile). 
3. EncodingRule: Applied to an encoded message (e.g. validation against a
2.xml Schema, a rule that prohibits empty tags, etc.).

We would attempt to ship HAPI with all the rules identified by the HL7
standard, enabled by default, and called at logical points in message
processing.  Users could disable the rules, call the rules programmatically
at different points in their own code, and create their own rules if they
wish.  Rules could be turned on and off at run-time, possibly by editing a
property file with one entry per class, like this (the entries below refer
to implementations of DataTypeRule):

ca.uhn.hl7v2.validation.datatype.TNFollowsNorthAmericanFormat = off
ca.uhn.hl7v2.validation.datatype.TNFollowsUKFormat = on

The beginnings of a suggested class structure are attached.  

Is anyone else interested in working on this?  Feedback is most welcome.  

Thanks, 
Bryan 


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