diff --git a/pdb-api/src/main/java/org/lucares/pdb/api/StringCompressor.java b/pdb-api/src/main/java/org/lucares/pdb/api/StringCompressor.java
index bdd44db..1db4e2d 100644
--- a/pdb-api/src/main/java/org/lucares/pdb/api/StringCompressor.java
+++ b/pdb-api/src/main/java/org/lucares/pdb/api/StringCompressor.java
@@ -8,6 +8,8 @@ import java.util.function.Function;
  */
 public class StringCompressor {
 
+    private static final String DEFAULT_GROUP = "<none>";
+
     private final UniqueStringIntegerPairs usip;
 
     public StringCompressor(final UniqueStringIntegerPairs usip) throws RuntimeIOException {
@@ -119,4 +121,18 @@ public class StringCompressor {
         return result;
     }
 
+    public String asValueString(final Tags tags) {
+        final StringBuilder result = new StringBuilder();
+        if (tags.isEmpty()) {
+            result.append(DEFAULT_GROUP);
+        } else {
+            tags.forEach((k, v) -> {
+                if (result.length() > 0) {
+                    result.append(" / ");
+                }
+                result.append(v);
+            });
+        }
+        return result.toString();
+    }
 }
diff --git a/pdb-api/src/main/java/org/lucares/pdb/api/Tags.java b/pdb-api/src/main/java/org/lucares/pdb/api/Tags.java
index 78bdaaa..9308d4b 100644
--- a/pdb-api/src/main/java/org/lucares/pdb/api/Tags.java
+++ b/pdb-api/src/main/java/org/lucares/pdb/api/Tags.java
@@ -175,15 +175,6 @@ public class Tags implements Comparable<Tags> {
         return tags;
     }
 
-    public void forEach(final BiConsumer<String, String> keyValueConsumer) {
-
-        for (final Tag tag : tags) {
-            final String key = STRING_COMPRESSOR.get(tag.getKey());
-            final String value = STRING_COMPRESSOR.get(tag.getValue());
-            keyValueConsumer.accept(key, value);
-        }
-    }
-
     public Tags mapTags(final Function<Tag, Tag> tagMapFuntion) {
         final List<Tag> mappedTags = new ArrayList<>(tags.size());
         for (final Tag tag : tags) {
@@ -244,9 +235,24 @@ public class Tags implements Comparable<Tags> {
         return tags.isEmpty();
     }
 
+//    TODO move
+//    to StringCompressor
+
+    public void forEach(final BiConsumer<String, String> keyValueConsumer) {
+
+        for (final Tag tag : tags) {
+            final String key = STRING_COMPRESSOR.get(tag.getKey());
+            final String value = STRING_COMPRESSOR.get(tag.getValue());
+            keyValueConsumer.accept(key, value);
+        }
+    }
+
     /**
      * @return User facing readable representation
      */
+//    TODO move
+//    to StringCompressor
+
     public String asString() {
 
         final StringBuilder result = new StringBuilder();
@@ -264,18 +270,21 @@ public class Tags implements Comparable<Tags> {
         return result.toString();
     }
 
-    public String asValueString() {
-        final StringBuilder result = new StringBuilder();
-        if (isEmpty()) {
-            result.append(DEFAULT_GROUP);
-        } else {
-            forEach((k, v) -> {
-                if (result.length() > 0) {
-                    result.append(" / ");
-                }
-                result.append(v);
-            });
-        }
-        return result.toString();
-    }
+//    TODO move
+//    to StringCompressor
+//
+//    public String asValueString() {
+//        final StringBuilder result = new StringBuilder();
+//        if (isEmpty()) {
+//            result.append(DEFAULT_GROUP);
+//        } else {
+//            forEach((k, v) -> {
+//                if (result.length() > 0) {
+//                    result.append(" / ");
+//                }
+//                result.append(v);
+//            });
+//        }
+//        return result.toString();
+//    }
 }
diff --git a/pdb-plotting/src/main/java/org/lucares/recommind/logs/Plotter.java b/pdb-plotting/src/main/java/org/lucares/recommind/logs/Plotter.java
index f3ad073..e132a25 100644
--- a/pdb-plotting/src/main/java/org/lucares/recommind/logs/Plotter.java
+++ b/pdb-plotting/src/main/java/org/lucares/recommind/logs/Plotter.java
@@ -208,7 +208,7 @@ public class Plotter {
     static String title(final Tags tags, final CsvSummary csvSummary) {
         // TODO title must be computed by the AggregateHandler, because it is the only
         // one knowing how many values are plotted
-        final StringBuilder result = new StringBuilder(tags.asValueString());
+        final StringBuilder result = new StringBuilder(Tags.STRING_COMPRESSOR.asValueString(tags));
 
         final int values = csvSummary.getValues();
         result.append(" (");