Before explaining the mechanics of CESs and how can CESs contribute in enriching the cloud environments, an insight of how services are utilized and incorporated in production clouds is essential. As shown in figure 1, WS are used mainly to interface the cloud offerings to the cloud users. These services cover all the spectrum of SaaS, PaaS and IaaS. These WS have the following characteristics:
a) Limited in number, fast learning curve and fully documented.
b) Do not need the traditional registering, querying and indexing.
c) Accessible from outside the cloud. Also accessible from other WS interfaces in the same cloud (e.g. Amazon’s EC2[1] can use simpleDB as part of the same solution).