Cloud Computing Service Engagement

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This specification was published by the W3C Cloud Computing Community Group. It is not a W3C Standard nor is it on the W3C Standards Track. Please note that under the W3C Community Contributor License Agreement (CLA). There is a limited opt-out and other conditions apply. Learn more about W3C Community and Business Groups


This specification details the procedure required to "engage" (that is, to initialise the use of) a cloud service.

Generally, this procedure consists of:

  • A cloud consumer sends a "service query" to listening cloud services, asking for the charging regime of each
  • Each of these these listening services then reach responds, in turn, with a rule-set supplying the requested information.
  • The consumer selects the desired service from those responding services, using whatever selection criteria is appropriate to that consumer

Once engaged, the consumer may then, as required, repeatedly send a "work request" (awwsee below) to that service.


This specification, code examples uses the following default namespace: ""

RIF, the Rule interchange Format, used in the selection of services, uses the following namespace: ""

The Service Query

A service Query is sent by a cloud consumer in an attempt find an appropriate cloud service to whom future work requests will be sent

This query consists of an "all routers" multicast request, to which listening services send a response consisting of an XML document representing a ruie-set, drawn from the Core sub-set of RIF, which will, when implemented, yield the charging regime of the service, expressed in units of US cents per GHz-minute

In this way, a consumer is able to, by knowing the required amount of computation, estimate the cost imposed by each service for the desired work

the consumer, after receiving all responses from "interested" cloud services, may then choose from among those services using whatever selection policy is desired.

MNote that the charging regime provided by a cloud service is purely a guide: consumers are not required to implement a RIF processor in order to make a service selection

The Work Request

Once a cloud service has been engaged, the intention of a consumer to have thatservice perform some computational work is communicated in the form of a "work request".

YThis request consists of an XML document, itself consisting of a single element having the tag WorkRequest", an attribute "style" containing the requested computation "style" (see below) and an attribute "model" containing a reference (as either a URL or absolute path) to a model of the computation to execute

Computation "Style"

The "style" with which a computation takes place consists of the minimum "availability" of the computation which, itself, consisting of a proportion of some period, expressed as a percentage, over which a computation is expected to be running and responsive.

The availability of a computation is calculated as follows, where "MTTF" is Mean Time to Failure and "MTTR" is Mean Time to Repair:

<math>(MTTF\div MTTR) \times 100</math>

The "Availability" Property

Availability is expressed in the form of a CSS property named "availability", associated with a selector representing the portion of the model to which that availability applies