Computerized information handling has changed its focus from centralized data
management systems to decentralized data exchange facilities. Modern distribu-
tion channels, such as high-speed Internet networks and wireless communication
infrastructures, provide reliable technical support for data distribution and data
access, materializing the new, popular idea that data may be available to any-
body, anywhere, anytime. However, providing huge amounts of data on request
often turns into a counterproductive service, making the data useless because
of poor relevance or inappropriate level of detail. Semantic knowledge is the es-
sential missing piece that allows the delivery of information that matches user
requirements. Semantic agreement, in particular, is essential to meaningful data
exchange.