Having a good HL7 specification document can be an extremely powerful tool for doing business with your hospital customers. One thing that it is very helpful is to try and prevent your customers from pushing unwanted time and effort on to your Primary Integration Engineers through uncontrolled change requests.

With respect to the outgoing streams of data the basic rule of thumb is to adhere as closely to the standard as possible and try not to be too flexible.

With incoming streams of data the use of Chameleon makes it easier to be very flexible in what kind of format the data comes in.

As a result the HL7 specification document you produce should be extremely detailed about what format of HL7 your application produces and how it is structured (note: you can use Chameleon's documentation capabilities to generate the skeleton of this document for you). Early in the contract process the customer should be encouraged to sign off on it so that later on they are not able to request changes without a change request being issued which results in billable time.

For the incoming data, the specification can be more general since it is usually quite easy to take the streams 'as is' and account for variations by adjusting the interface configuration file ("VMD file") using the Chameleon IDE.