Interoperability is an important problem in the healthcare informatics domain since most of the health information systems are proprietary.

Interoperability can be addressed in two levels:

   1) Functional (syntactic) level interoperability is the ability of two or more systems to exchange information. This involves agreeing on the common network protocols such as Internet or Value Added Networks; the transport binding such as HTTP, FTP, SMT, etc. and the message format like XML (Extensible Markup Language) or EDI (Electronic Data Interchange).

   2) Semantic level interoperability, on the other hand, is the ability for information shared by systems to be understood at the level of formally defined domain concepts so that the information is computer processable by the receiving system.

Currently the most promising functional interoperability technology is the Web Services. Web services are application functions that can be programmatically invoked over the Internet. The information that an application must have in order to programmatically invoke a Web service is defined by two universally accepted standards: Web Services Description Language (WSDL) and Simple Object Access Protocol (SOAP). WSDL of a Web service defines its interface and establishes its public contract with the outside world. The network protocol used is usually http and binding is SOAP.

The importance of Web services in providing functional interoperability has been recognized by the healthcare industry and recently Integrating Healthcare Enterprise (IHE) initiative has proposed a set of Web services for some of the basic functionality in healthcare information systems. Also HL7 has recently approved Web services and ebXML standards as “draft standards for trial use”.

However for full machine interoperability we also need to define the semantic level interoperability. In Web service technology this translates to describing the semantics of Web services. Semantics is domain specific knowledge and medical informatics is one of the few domains to have considerable domain knowledge exposed through standards.

In this talk, I will describe the architecture of the Artemis project, which exploits ontologies based on the domain knowledge exposed by the healthcare information standards like HL7, CEN TC251, ISO TC215 and GEHR. I will explain how these standards can be used in expressing the semantics of both the functionality of Web services (i.e., what a Web service does) and the semantics of the messages they exchange.

The Artemis interoperability architecture does not propose globally agreed ontologies; rather healthcare institutes reconcile their semantic differences through a mediator component. The mediator component uses ontologies based on prominent healthcare standards as references to facilitate semantic mediation among involved institutes. Artemis mediators have a P2P communication architecture to provide scalability and to facilitate the discovery of other mediators.