The componentization of information technology, starting in the 1980s and affecting GIS in the 1990s, raises the question of how software components can interact with each other. Semantic interoperability is the capability of software components to interact without misunderstandings. People share work by agreeing on “interfaces” between their individual parts (i.e., roles), together with conditions on what shall be delivered across these interfaces, at what time, and in what form and quality. Everybody has had the experience of how essential it is to specify such agreements in a way that avoids misunderstandings. As with software components, we are only just learning how to structure such agreements.

Today's software developers assemble programs from chunks of software and data, called services, developed by others and over which they ...