Composite as Metamodel: a Design Pattern for Implementing SIGOBT-style Object Wrappers for HL7 Messages

As part of our efforts to develop applications for our collaborators in the Singapore healthcare industry, we have developed a component library for HL7 interfaces [HL7 1997]. This library follows the recommendations of [SIGOBT1998] in the definition of its software interfaces, and the Encoding Rules and Lower Layer Protocol recommendations in the implementation of its parsing, generation and transport of HL7 messages. The topic of this paper is the design of the library and what its design shares with that of two other libraries, ProtoGen [Schadow1996a] [Schadow1996b] and the MS-HUG Implementation of SIGOBT [MSHUG1997a] [MSHUG1997b]; in other words, the design pattern they all follow.