  Analogous to living ecosystems in nature, web services form an artificial
ecosystem consisting of many tags and their associated media, such as
photographs, movies, and web pages created by human users. Concerning
biological ecosystems, we regard tag as a species and human as a hidden
environmental resource. We subsequently analyze the evolution of the web
services, in particular social tagging systems, with respect to the
self-organization of new tags. The evolution of new combinations of tags is
analyzed as the open-ended evolution (OEE) index. The tag meaning is computed
by the types of associated tags; tags that vary their meanings temporally
exist. We argue that such tags are the examples of OEE.
