diff --git a/com.minres.scviewer.database.leveldb/src/com/minres/scviewer/database/leveldb/LevelDBLoader.java b/com.minres.scviewer.database.leveldb/src/com/minres/scviewer/database/leveldb/LevelDBLoader.java
index 8f7ee35..c5c844a 100644
--- a/com.minres.scviewer.database.leveldb/src/com/minres/scviewer/database/leveldb/LevelDBLoader.java
+++ b/com.minres.scviewer.database.leveldb/src/com/minres/scviewer/database/leveldb/LevelDBLoader.java
@@ -64,7 +64,7 @@ public class LevelDBLoader implements IWaveformDbLoader {
 	}
 
 	@Override
-	public List<IWaveform> getAllWaves() {
+	public Collection<IWaveform> getAllWaves() {
 		List<IWaveform> streams=new ArrayList<IWaveform>();
 		SeekingIterator<String, String> it = levelDb.iterator();
 		it.seek("s~");
diff --git a/com.minres.scviewer.database.sqlite/src/com/minres/scviewer/database/sqlite/SQLiteDbLoader.java b/com.minres.scviewer.database.sqlite/src/com/minres/scviewer/database/sqlite/SQLiteDbLoader.java
index d90f686..a1f2ac6 100644
--- a/com.minres.scviewer.database.sqlite/src/com/minres/scviewer/database/sqlite/SQLiteDbLoader.java
+++ b/com.minres.scviewer.database.sqlite/src/com/minres/scviewer/database/sqlite/SQLiteDbLoader.java
@@ -61,7 +61,7 @@ public class SQLiteDbLoader implements IWaveformDbLoader {
 	}
 
 	@Override
-	public List<IWaveform> getAllWaves() {
+	public Collection<IWaveform> getAllWaves() {
 		SQLiteDatabaseSelectHandler<ScvStream> handler = new SQLiteDatabaseSelectHandler<ScvStream>(ScvStream.class, database);
 		List<IWaveform> streams=new ArrayList<IWaveform>();
 		try {
diff --git a/com.minres.scviewer.database.text/src/com/minres/scviewer/database/text/TextDbLoader.groovy b/com.minres.scviewer.database.text/src/com/minres/scviewer/database/text/TextDbLoader.groovy
index 2ae1676..3b3a45a 100644
--- a/com.minres.scviewer.database.text/src/com/minres/scviewer/database/text/TextDbLoader.groovy
+++ b/com.minres.scviewer.database.text/src/com/minres/scviewer/database/text/TextDbLoader.groovy
@@ -50,8 +50,8 @@ public class TextDbLoader implements IWaveformDbLoader{
 	}
 
 	@Override
-	public List<IWaveform> getAllWaves() {
-		return new LinkedList<IWaveform>(streams);
+	public Collection<IWaveform> getAllWaves() {
+		return streams;
 	}
 
 	public Map<Long, ITxGenerator> getGeneratorsById() {
diff --git a/com.minres.scviewer.database.vcd/src/com/minres/scviewer/database/vcd/VCDDbLoader.java b/com.minres.scviewer.database.vcd/src/com/minres/scviewer/database/vcd/VCDDbLoader.java
index a0f12db..fb7f474 100644
--- a/com.minres.scviewer.database.vcd/src/com/minres/scviewer/database/vcd/VCDDbLoader.java
+++ b/com.minres.scviewer.database.vcd/src/com/minres/scviewer/database/vcd/VCDDbLoader.java
@@ -128,7 +128,7 @@ public class VCDDbLoader implements IWaveformDbLoader, IVCDDatabaseBuilder {
 	 * @see com.minres.scviewer.database.ITrDb#getAllWaves()
 	 */
 	@Override
-	public List<IWaveform> getAllWaves() {
+	public Collection<IWaveform> getAllWaves() {
 		return signals;
 	}
 
diff --git a/com.minres.scviewer.database/src/com/minres/scviewer/database/IWaveformDbLoader.java b/com.minres.scviewer.database/src/com/minres/scviewer/database/IWaveformDbLoader.java
index 16f897d..1ccba07 100644
--- a/com.minres.scviewer.database/src/com/minres/scviewer/database/IWaveformDbLoader.java
+++ b/com.minres.scviewer.database/src/com/minres/scviewer/database/IWaveformDbLoader.java
@@ -12,7 +12,6 @@ package com.minres.scviewer.database;
 
 import java.io.File;
 import java.util.Collection;
-import java.util.List;
 
 public interface IWaveformDbLoader {
 	
@@ -20,7 +19,7 @@ public interface IWaveformDbLoader {
 	
 	public Long getMaxTime();
 	
-	public List<IWaveform> getAllWaves() ;
+	public Collection<IWaveform> getAllWaves() ;
 	
 	public Collection<RelationType> getAllRelationTypes() ;