public void setPurgingEnabled(boolean purgingEnabled) {
        this.incrementalDataPurging = purgingEnabled;
    }
This method get the onDemandQuery and return the corresponding output and its types.

@param onDemandQuery       this onDemandQuery is processed and get the output attributes.
@param onDemandQueryString this passed to report errors with context if there are any.
@return List of output attributes
modules/siddhi-core/src/main/java/io/siddhi/core/SiddhiAppRuntimeImpl.java