When it comes to defining Cloud Computing I typically take the stance of "I know it when I see it". Although I'm half joking, being able to spot an Internet centric platform or infrastructure is fairly self evident for the most part. But when it comes to an "OpenCloud API" things get a little more difficult.
Lately it seems that everyone is releasing their own "OpenCloud API's", companies like GoGrid and Sun Microsystems were among the first to embrace this approach offering there API's under friendly open creative common licenses. The key aspect in most of these CC licensed API's is the requirement that attribution is given to the original author or company. Although personally I would argue that a CC license isn't completely open because of this attribution requirement, but at the end of the day it's probably open enough.
For some background, a Cloud API determines the vocabulary / taxonomy that a programmer needs employ when using a particular set of cloud services. To be clear, an API is only the documents and processes for the usage of a certain cloud API, without these there is no API. In a recent twitter post Simon Wardley said it this way, "Companies can't own APIs only the documentation, tools and processes (which are generic to the API)."
Generally there are three types of Cloud API's.
1. Blind API's - API's that don't tell you their restrictions. Amazon Web Services is the best example. (Personally I'd rather know what I can or can't do then not know at all)
3. OpenCloud API's - API's that generally let you do whatever you want as long as you give attribution. Rackspace, GoGrid and Sun are the best examples. A major issue facing a lot of these so called open API's is although you maybe free to remix and use the API, you could be limited by the use of a company's name or trademark. Making the attribution clause a potential mine field.
I'd like to also note that a sub branch of OpenCloud API's are Open Community API's such as the OGF's OCCI project. These community API's apply an open source model that allow anyone to get involved in the development and specifications of a Cloud API at little or no cost.
This brings us to what exactly is an OpenCloud API?
A Cloud API that is free of restrictions, be it usage, cost or otherwise.