[Feature] Communication with service [Webinos proposal] A standardized / “well-known” JavaScript API is provided to the web application to access the service. [Opera/CableLabs proposal] A URL, extracted directly from the underlying service discovery process, is provided to the web application to access the service. The web page can then use standard XmlHttpRequest, Web Sockets, Server-Sent Events and Web Messaging, etc (all with implicit cross-origin resource sharing) to communcate with the service. Protocol depends on messaging format implemented in device implementing service (e.g. json, protobufs, text-based, xml, etc). [Google Web Intents] Data is sent bi-directionally between client web application page and the service web page through the Web Intents API. The format/protocol of this data exchange is defined for each Action by the Web Intents specification. Underlying communication mechanism is web messaging but this level is hided to the application developer. [Google Web Introducer] 
Data is sent bi-directionally between client web application page and the service web page through Web Messaging. The format/protocol of this data exchange must be defined for each Intent by specific API/protocol specifications for each intent type.