diff --git a/tabula-core/src/main/java/de/tudresden/inf/lat/tabula/table/TableMap.java b/tabula-core/src/main/java/de/tudresden/inf/lat/tabula/table/TableMap.java
index dc1a70c..927d219 100644
--- a/tabula-core/src/main/java/de/tudresden/inf/lat/tabula/table/TableMap.java
+++ b/tabula-core/src/main/java/de/tudresden/inf/lat/tabula/table/TableMap.java
@@ -23,15 +23,19 @@ public interface TableMap {
 	 *            identifier
 	 * @param table
 	 *            table
+	 * @return an optional containing the previous value associated to the given
+	 *         key, or an empty optional if there was no association before
 	 */
-	void put(String id, Table table);
+	Optional<Table> put(String id, Table table);
 
 	/**
-	 * Returns the table associated to the given identifier.
+	 * Returns an optional containing the value associated to the given key, or
+	 * an empty optional if there is no association.
 	 * 
 	 * @param id
 	 *            identifier
-	 * @return the table associated to the given identifier
+	 * @return an optional containing the value associated to the given key, or
+	 *         an empty optional if there is no association
 	 */
 	Optional<Table> getTable(String id);
 
diff --git a/tabula-core/src/main/java/de/tudresden/inf/lat/tabula/table/TableMapImpl.java b/tabula-core/src/main/java/de/tudresden/inf/lat/tabula/table/TableMapImpl.java
index 01111fa..8dd4790 100644
--- a/tabula-core/src/main/java/de/tudresden/inf/lat/tabula/table/TableMapImpl.java
+++ b/tabula-core/src/main/java/de/tudresden/inf/lat/tabula/table/TableMapImpl.java
@@ -32,11 +32,6 @@ public TableMapImpl(TableMap otherTableMap) {
 		otherTableMap.getTableIds().forEach(tableId -> put(tableId, otherTableMap.getTable(tableId).get()));
 	}
 
-	/**
-	 * Returns the identifiers of the stored tables.
-	 * 
-	 * @return the identifiers of the stored tables
-	 */
 	@Override
 	public List<String> getTableIds() {
 		List<String> ret = new ArrayList<>();
@@ -44,26 +39,11 @@ public List<String> getTableIds() {
 		return ret;
 	}
 
-	/**
-	 * Stores a table with the given identifier.
-	 * 
-	 * @param id
-	 *            identifier
-	 * @param table
-	 *            table
-	 */
 	@Override
-	public void put(String id, Table table) {
-		this.map.putOpt(id, table);
+	public Optional<Table> put(String id, Table table) {
+		return this.map.putOpt(id, table);
 	}
 
-	/**
-	 * Returns the table associated to the given identifier.
-	 * 
-	 * @param id
-	 *            identifier
-	 * @return the table associated to the given identifier
-	 */
 	@Override
 	public Optional<Table> getTable(String id) {
 		return this.map.getOpt(id);