When aggregating data, Commerce Reference Store creates an actor chain that uses other nested actor chains. For example, in the actor ProductCatalogActor for Store.Mobile.REST:

  <actor-chain id="sendViewItemEventGetRecentlyViewedProducts">
    <droplet id="productLookup" name="/atg/commerce/catalog/ProductLookup" var="productLookupParamStack">
      <input name="id" value="${(productId != null) ? productId : param.productId}" />
      <input name="filterBySite" value="false" />
      <oparam name="output">
        <droplet id="productBrowsed" name="/atg/commerce/catalog/ProductBrowsed">
          <input name="eventobject" value="${productLookupParamStack.element}" />
        </droplet>
      </oparam>
    </droplet>

    <actor id="recentlyViewedProducts" name="/atg/commerce/catalog/ProductCatalogActor"
      chain-id="getRecentlyViewedProducts" return-model-var="recentlyViewedProducts">
      <!-- inputs will come from the request parameters -->
      <output id="recentlyViewedProducts" name="recentlyViewedProducts"
        value="${recentlyViewedProducts.recentlyViewedProducts}" />
    </actor>
  </actor-chain>

The actor ProductCatalogActor for Store.Mobile.REST sends a view item event and then uses the nested actor ProductCatalogActor.getRecentlyViewedProducts.

This example uses a request parameter to determine if the user wants recentlyViewedProducts with the product item output:

<!-- optionally return recently viewed products along with the product -->
  <!-- also add list of properties that you can 'choose' to select a SKU (e.g. color, size) -->
  <actor-chain id="outputProduct">
    <droplet id="skuProperties" name="/atg/dynamo/droplet/ForEach" var="forEachProperty">
      <input name="array" value="${nucleus['/atg/commerce/catalog/CatalogTools'].propertyToLabelMap}" />
      <oparam name="output">
        <output id="skuProperties" name="product.skuProperties[${forEachProperty.index}]" value="${forEachProperty.key}" />
      </oparam>
    </droplet>
    <droplet id="switch" name="/atg/dynamo/droplet/Switch" var="switch">
      <input name="value" value="${param.getRecentlyViewedProducts}" />
      <oparam name="true">
        <actor id="recentlyViewedProducts" name="/atg/commerce/catalog/ProductCatalogActor"
          chain-id="getRecentlyViewedProducts" return-model-var="recentlyViewedProducts">
          <!-- inputs come from request parameters -->
          <output id="recentlyViewedProducts" name="recentlyViewedProducts" value="${recentlyViewedProducts.recentlyViewedProducts}"/>
        </actor>
      </oparam>
    </droplet>
  </actor-chain>