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What is ProtoGen/HL7?

ProtoGen/HL7 is a C++ application programming interface (API) to the HL7 standard for the communication of clinical data. In the terminology of C++ ProtoGen/HL7 is a class library that defines data according to the HL7 data model plus methods that provide various access to the data structure. However, ProtoGen/HL7 is not just the class library, it is also a compiler that builds this library from the textual document which is the official HL7 standard. The latter is, what the Name ProtoGen/HL7 wants to express: it is a Protocol implementation Generator for HL7.

An implementation of a communication standard is essentially a data structure, a builder and a parser. The data structure holds the data objects and reflects their relations among each other as assumed by the standard. The builder is to produce a valid representation of the data structure that is capable of being transported via electronic data interchange media. Finally the parser transforms this representation back into the data structure.

This implementation tries to assume models and methods of todays informatics technology. It's design is object oriented and is implementeted using C++. The code of the implementation is produced by a compiler whose input is a database which specifies the standard. The database is in turn compiled semi-automatically by scanning the text of the HL7 standard as is released by the HL7 Working Group. This method of generating the implementation directly from the textual description has the following advantages: correctness and customizability of both, the parser/builder methods and the definition of the standard itself.

Since the specifying database as well as the program code which implements the standard is not written manually but produced by a compiler, the output is assured to be correct, unless the compiler itself is incorrect. An incorrect compiler, however, will result in erroneous code but the errors tend to occur systematically rather than accidentially and are thus discovered more easily. Thus the method of ProtoGen/HL7 can be used to generate a HL7 reference implementation. On the other hand, it does reveal problems and errors in the standard definition itself, since a compiler will not guess the intended meaning of an ambiguous or obviously incorrect passage as a human programmer would probably do.

The input database for the ProtoGen/HL7 compiler is customizable and allows the user to add new data elements quite easily. For example, a special Z-segment that is used by a site can be added to the standard just by adding a few line to the database. The implementation for this special segment is generated fully automatically as is the implementation of the whole standard.

On the other hand, the methods of the parser/builder may be customized in order to provide for different encoding rules or to speed up the implementation or tune it for size. These customizations are, however, not done very often and can currently only be done with a deeper understanding of the compiler itself since this requires the compiler program to be modified. Nevertheless, there are various applications that can be worth the effort ranging from modifications to HL7 coding or processing rules up to the implementation of a completely different standard. Since the UN EDIFACT encoding rules are quite similar to those of HL7 there could be an EDIFACT module added to ProtoGen with only a little to moderate effort.

Finally, the object oriented model of the HL7 standard that this implementation assumes helps to stay compatible with the new developement in the HL7 Working Group (version 3.0) in particular as well as health care data interchange standards of the future in general, such as MEDIX.

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