The ‘when’ expression will trigger a consequence when a condition is met, like in

    <when test="${variable:over} == true">
        <participant ref="toto" />
    </when>

where the participant "toto" will receive a workitem when the (local) variable "over" has the value true.

This is also possible :

    <when>
        <equals field-value="done" other-value="true" />
        <participant ref="toto" />
    </when>

The ‘when’ expression by defaults, evaluates every 10 seconds its condition clause. A different frequency can be stated via the "frequency" attribute :

    _when :test => "${completion_level} == 4", :frequency => "1s"
        participant "next_stage"
    end

will check for the completion_level value every second. The scheduler itself is by default ‘waking up’ every 250 ms, so setting a frequency to something smaller than that value might prove useless. (Note than in the Ruby process definition, the ‘when’ got escaped to ‘_when’ not to conflict with the ‘when’ keyword of the Ruby language).

The when expression understands the ‘timeout’ attribute like the participant expression does. Thus

    _when :test => "${cows} == 'do fly'", :timeout => "1y"
        participant "me"
    end

will timeout after one year (participant "me" will not receive a workitem).