The Coordinator application runs many times during the span of start time and end time. A Coordinator action uses creation (materialization) time to find the specific Dataset instances that are required for its input and output events.
The following EL functions are used to relate the Coordinator action creation time to the Dataset instances of its input and output events.
The current(int n) function gives us the nth Dataset instance for a synchronous Dataset, relative to the Coordinator action creation time.
For example, current(1) represents the instance, which is calculated after adding the start time with the frequency.
In our case, current(1) of rainfall is resolved to /user/hue/learn_oozie/ch05/input/rainfall/2015/01. This was resolved at the end of month of January.
<data-in name="wf_input" dataset="rainfall">
<instance>${coord:current(0)}</instance>
</data-in>
