--- a/artifacts/doc/conf/cache.xml	Wed Oct 30 15:02:16 2013 +0100
+++ b/artifacts/doc/conf/cache.xml	Wed Oct 30 15:26:21 2013 +0100
@@ -76,6 +76,16 @@
            memoryStoreEvictionPolicy="LFU"
            />
 
+    <!-- This one is used to cache the recommendation nodes generated from datacage -->
+    <cache name="recommendations"
+           maxElementsInMemory="150"
+           eternal="false"
+           timeToLiveSeconds="1800"
+           memoryStoreEvictionPolicy="LRU"
+           overflowToDisk="false"
+           diskPersistent="false"
+       />
+
     <!-- This one is used for the cross section next neighbor lookup -->
     <cache name="cross-section-kms"
            maxElementsInMemory="50"
@@ -149,7 +159,8 @@
     <cache name="official-lines"
            maxElementsInMemory="2"
            timeToLiveSeconds="14400"
-           />
+       />
+
 
     <!-- This one is used for the cross section lookup
          Because of lazy fetching and relatively big amount of data, disabled

--- a/artifacts/src/main/java/org/dive4elements/river/artifacts/CollectionMonitor.java	Wed Oct 30 15:02:16 2013 +0100
+++ b/artifacts/src/main/java/org/dive4elements/river/artifacts/CollectionMonitor.java	Wed Oct 30 15:26:21 2013 +0100
@@ -12,6 +12,8 @@
 import java.util.List;
 import java.util.Map;
 
+import net.sf.ehcache.Cache;
+
 import org.w3c.dom.Document;
 import org.w3c.dom.Element;
 import org.w3c.dom.Node;
@@ -22,15 +24,19 @@
 import org.dive4elements.artifacts.CallContext;
 import org.dive4elements.artifacts.Hook;
 
+import org.dive4elements.artifacts.common.utils.XMLUtils;
 import org.dive4elements.artifacts.common.utils.XMLUtils.ElementCreator;
 
 import org.dive4elements.artifactdatabase.state.Output;
 
+import org.dive4elements.river.artifacts.cache.CacheFactory;
 import org.dive4elements.river.artifacts.datacage.Recommendations;
 
 /** Monitors collection changes. */
 public class CollectionMonitor implements Hook {
 
+    public static final String CACHE_NAME = "recommendations";
+
     @Override
     public void setup(Node cfg) {
     }
@@ -55,23 +61,70 @@
 
         Element result = (Element)results.item(0);
 
+        result.appendChild(getRecommendedElement(flys, context, doc));
+    }
+
+    protected Element getRecommendedElement(
+        D4EArtifact artifact,
+        CallContext context,
+        Document    doc
+    ) {
+        String [] outs = extractOutputNames(artifact, context);
+
+        Element recommendations = null;
+
+        Cache cache = CacheFactory.getCache(CACHE_NAME);
+
+        if (cache != null) {
+            String key = generateCacheKey(artifact, outs);
+
+            net.sf.ehcache.Element ce = cache.get(key);
+            if (ce != null) { // Found in cache.
+                Element e = (Element)ce.getValue();
+                // Sync to avoid thread issues with XML DOM docs.
+                synchronized (e.getOwnerDocument()) {
+                    recommendations = (Element)doc.importNode(e, true);
+                }
+            } else { // Not found in cache -> generate it.
+                Element r = createElement(XMLUtils.newDocument());
+
+                Recommendations.getInstance().recommend(
+                    artifact, null, outs,
+                    getNoneUserSpecificParameters(artifact, context), r);
+
+                recommendations = (Element)doc.importNode(r, true);
+
+                cache.put(new net.sf.ehcache.Element(key, r));
+            }
+        } else { // No cache configured -> append directly.
+
+            recommendations = createElement(doc);
+
+            Recommendations.getInstance().recommend(
+                artifact, null, outs,
+                getNoneUserSpecificParameters(artifact, context),
+                recommendations);
+        }
+
+        return recommendations;
+    }
+
+    private static final Element createElement(Document doc) {
         ElementCreator creator = new ElementCreator(
             doc,
             ArtifactNamespaceContext.NAMESPACE_URI,
             ArtifactNamespaceContext.NAMESPACE_PREFIX);
 
-        Element recommended = creator.create("recommended-artifacts");
-
-        String[] outs              = extractOutputNames(flys, context);
-        Map<String, Object> params = getNoneUserSpecificParameters(flys, context);
+        return creator.create("recommended-artifacts");
+    }
 
-        Recommendations rec = Recommendations.getInstance();
-
-        // TODO For newer official-lines recommendations we actually
-        // need user-id (null here).
-        rec.recommend(flys, null, outs, params, recommended);
-
-        result.appendChild(recommended);
+    private static final String generateCacheKey(D4EArtifact artifact, String [] outs) {
+        StringBuilder sb = new StringBuilder(artifact.hash());
+        // XXX: The hash really should be unique enough.
+        for (String out: outs) {
+            sb.append(';').append(out);
+        }
+        return sb.toString();
     }
 
 
@@ -79,7 +132,7 @@
      * Get outputnames from current state (only the ones for which
      * facets exist).
      */
-    public static String[] extractOutputNames(
+    private static final String [] extractOutputNames(
         D4EArtifact flys,
         CallContext  context)
     {
@@ -104,11 +157,11 @@
     /**
      * Creates Map from Strings "recommended" to "true".
      */
-    protected Map<String, Object> getNoneUserSpecificParameters(
+    private static final Map<String, Object> getNoneUserSpecificParameters(
         D4EArtifact flys,
-        CallContext  context)
+        CallContext context)
     {
-        Map<String, Object> params = new HashMap<String, Object>(1);
+        Map<String, Object> params = new HashMap<String, Object>();
         params.put("recommended", "true");
 
         return params;