A platform (1) allows end users to engage in a session with servers such as content providers, corporate systems, commercial services or ASPs. A session object is associated with each session, attributes of which include the channel--thereby allowing changing of a channel during a session. Request/event objects are associated with the session object as requests/notifications arise, and these objects are shared with other modules. Hosted services may be physically resident on the platform or may be accessed transparently via interfaces. A device/channel neutral mark-up language extended from a presentation mark-up language is used as a single common form from which the delivered content is derived. The content from a service is generated by an executable process, normally (but not exclusively) in the extended mark-up language. The derivation of deliverable content is performed via a dynamic and configurable sequence of providers that manipulate the original content in stages.