Common Tag is an open tagging format developed to make content more connected, discoverable and engaging. Unlike free-text tags, Common Tags are references to unique, well-defined concepts, complete with metadata and their own URLs. With Common Tag, site owners can more easily create topic hubs, cross-promote their content, and enrich their pages with free data, images and widgets. The companies involved in the development of Common Tag — AdaptiveBlue, DERI (NUI Galway), Faviki, Freebase, Yahoo!, Zemanta, and Zigtag — offer services that help publishers get started.
The first stage involved text on web pages; the second stage does involve humans, who are helping identify images and adding context to web pages, which makes the web appear knowledgeable.
Buildings and infrastructure typically have sensors built in too. Strain gauges on bridges tell how well they are handling the stresses of their everyday existence; there are temperature sensors on cars, while rain gauges and gas samplers at any location will give you a picture of the world.