Health level 7 (HL7) is a standard for medical information exchange. It defines data transfers for the application systems in the healthcare environment. Alternatively, the extensible markup language (XML) is a standard for data exchange using the Internet. If exchange messages follow the content and the sequence defined by HL7 and are expressed in the XML format, the system may benefit from the advantages of both standards. In creating the XML schema, we found ambiguities in HL7 message structures that cause the XML schema to be non-deterministic. These ambiguous expressions are summarized within 12 structures and can be replaced with equivalent or similar unambiguous structures. The finite state automata are used to verify expression equivalence. Applying this schema, an XML document may eliminate redundant segment group definitions and make the structure simple and easy to reproduce. In this paper, we discuss the methods and our experience in resolving ambiguous problems in HL7 messages to generate a deterministic XML schema.
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