On Jan 19, 2009, at 2:33 PM, Stavros Panidis wrote:
my customer is a major department in a public hospital. Each time
they decide to perform an experiment and take in account different
measurements. No one can predict this. So they need to have the
ability to create and/or alter existing tables.
Hi Stavros,
We do a lot of similar systems for healthcare and the situation you're
describing is fairly typical, especially when dealing with clinical
data. I agree with Suzanne though, implementing it by changing the
underlying tables is a recipe for trouble. Too many other pieces like
validation, reports, data feeds, data cubes, etc get really
complicated when the schema starts changing and the data gets ragged.
Typically we'd start to model this problem with a metadata structure
like a Procedure entity (the header record), an Aspect entity (things
that can be measured in a procedure, valid ranges, expected data
types), and a ProcedureAspect entity (the value of a given Aspect for
a Procedure).
Adding entries to the Aspect table is akin to changing the database
schema...it defines which attributes you expect for a Procedure...and
that's easily done at runtime.
-John
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