diff --git a/src/EcsQuery.cs b/src/EcsQuery.cs
index 8935b5e..6c454e4 100644
--- a/src/EcsQuery.cs
+++ b/src/EcsQuery.cs
@@ -50,19 +50,19 @@ namespace DCFApixels.DragonECS
                 return (TQuery)(object)newQuery;
             }
 
-            public override inc_<TComponent> Include<TComponent>() where TComponent : struct
+            public sealed override TPool Include<TComponent, TPool>()
             {
                 _inc.Add(_world.GetComponentID<TComponent>());
-                return new inc_<TComponent>(_world.GetPool<TComponent, EcsPool<TComponent>>());
+                return _world.GetPool<TComponent, TPool>();
             }
-            public override exc_<TComponent> Exclude<TComponent>() where TComponent : struct
+            public sealed override TPool Exclude<TComponent, TPool>()
             {
                 _exc.Add(_world.GetComponentID<TComponent>());
-                return new exc_<TComponent>(_world.GetPool<TComponent, EcsPool<TComponent>>());
+                return _world.GetPool<TComponent, TPool>();
             }
-            public override opt_<TComponent> Optional<TComponent>() where TComponent : struct
+            public sealed override TPool Optional<TComponent, TPool>()
             {
-                return new opt_<TComponent>(_world.GetPool<TComponent, EcsPool<TComponent>>());
+                return _world.GetPool<TComponent, TPool>();
             }
 
             private void End(out EcsQueryMask mask)
@@ -77,20 +77,11 @@ namespace DCFApixels.DragonECS
         }
         #endregion
     }
-    public abstract class EcsHierarchyQuery : EcsQueryBase
+    public abstract class EcsJoinAttachQuery : EcsQueryBase
     {
-        private ProfilerMarker _getEnumerator = new ProfilerMarker("EcsHierarchyQuery.Execute");
+       // private EcsPool<Edge> attachPool;
 
-        protected override void OnBuildAfter() { }
-        public override void Execute()
-        {
-        }
-    }
-    public abstract class EcsGraphQuery : EcsQueryBase
-    {
-        private EcsPool<Edge> attachPool;
-
-        private ProfilerMarker _getEnumerator = new ProfilerMarker("EcsGraphQuery.Execute");
+        private ProfilerMarker _getEnumerator = new ProfilerMarker("EcsJoinAttachQuery.Execute");
         protected sealed override void OnBuildAfter()
         {
             throw new NotImplementedException();
@@ -108,6 +99,28 @@ namespace DCFApixels.DragonECS
             return groupFilter.GetEnumerator();
         } 
     }
+    public abstract class EcsJoinRelationQuery : EcsQueryBase
+    {
+        // private EcsPool<Edge> attachPool;
+
+        private ProfilerMarker _getEnumerator = new ProfilerMarker("EcsJoinAttachQuery.Execute");
+        protected sealed override void OnBuildAfter()
+        {
+            throw new NotImplementedException();
+            // attachPool = World.GetPool<Edge>();
+        }
+        public sealed override void Execute()
+        {
+            using (_getEnumerator.Auto())
+            {
+                throw new NotImplementedException();
+            }
+        }
+        public EcsGroup.Enumerator GetEnumerator()
+        {
+            return groupFilter.GetEnumerator();
+        }
+    }
 
     public abstract class EcsQuery : EcsQueryBase
     {
@@ -156,8 +169,8 @@ namespace DCFApixels.DragonECS
     }
     public abstract class EcsQueryBuilderBase
     {
-        public abstract inc_<TComponent> Include<TComponent>() where TComponent : struct;
-        public abstract exc_<TComponent> Exclude<TComponent>() where TComponent : struct;
-        public abstract opt_<TComponent> Optional<TComponent>() where TComponent : struct;
+        public abstract TPool Include<TComponent, TPool>() where TComponent : struct where TPool : EcsPoolBase, new();
+        public abstract TPool Exclude<TComponent, TPool>() where TComponent : struct where TPool : EcsPoolBase, new();
+        public abstract TPool Optional<TComponent, TPool>() where TComponent : struct where TPool : EcsPoolBase, new();
     }
 }
diff --git a/src/EcsQueryMember.cs b/src/EcsQueryMember.cs
deleted file mode 100644
index ccdd985..0000000
--- a/src/EcsQueryMember.cs
+++ /dev/null
@@ -1,84 +0,0 @@
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-
-namespace DCFApixels.DragonECS
-{
-    public interface IEcsQueryMember { }
-    public interface IEcsQueryReadonlyField<TComponent> : IEcsQueryMember
-    {
-        public ref readonly TComponent Read(ent entityID);
-        public bool Has(ent entityID);
-    }
-    public interface IEcsQueryField<TComponent> : IEcsQueryReadonlyField<TComponent>
-            where TComponent : struct
-    {
-        public ref TComponent Add(ent entityID);
-        public ref TComponent Write(ent entityID);
-        public void Del(ent entityID);
-    }
-
-    #region select
-    [StructLayout(LayoutKind.Sequential, Pack = 8, Size = 8)]
-    public readonly struct inc_<TComponent> : IEcsQueryField<TComponent>
-        where TComponent : struct
-    {
-        internal readonly EcsPool<TComponent> pool;
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal inc_(EcsPool<TComponent> pool) => this.pool = pool;
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public ref TComponent Add(ent entityID) => ref pool.Add(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public ref TComponent Write(ent entityID) => ref pool.Write(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public ref readonly TComponent Read(ent entityID) => ref pool.Read(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public bool Has(ent entityID) => pool.Has(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Del(ent entityID) => pool.Del(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static implicit operator inc_<TComponent>(EcsQueryBuilderBase buider) => buider.Include<TComponent>();
-    }
-
-    [StructLayout(LayoutKind.Sequential, Pack = 8, Size = 8)]
-    public readonly struct exc_<TComponent> : IEcsQueryField<TComponent>
-        where TComponent : struct
-    {
-        internal readonly EcsPool<TComponent> pool;
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal exc_(EcsPool<TComponent> pool) => this.pool = pool;
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public ref TComponent Add(ent entityID) => ref pool.Add(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public ref TComponent Write(ent entityID) => ref pool.Write(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public ref readonly TComponent Read(ent entityID) => ref pool.Read(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public bool Has(ent entityID) => pool.Has(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Del(ent entityID) => pool.Del(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static implicit operator exc_<TComponent>(EcsQueryBuilderBase buider) => buider.Exclude<TComponent>();
-    }
-
-    [StructLayout(LayoutKind.Sequential, Pack = 8, Size = 8)]
-    public readonly struct opt_<TComponent> : IEcsQueryField<TComponent>
-        where TComponent : struct
-    {
-        internal readonly EcsPool<TComponent> pool;
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal opt_(EcsPool<TComponent> pool) => this.pool = pool;
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public ref TComponent Add(ent entityID) => ref pool.Add(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public ref TComponent Write(ent entityID) => ref pool.Write(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public ref readonly TComponent Read(ent entityID) => ref pool.Read(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public bool Has(ent entityID) => pool.Has(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Del(ent entityID) => pool.Del(entityID.id);
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static implicit operator opt_<TComponent>(EcsQueryBuilderBase buider) => buider.Optional<TComponent>();
-    }
-    #endregion
-}
diff --git a/src/Exceptions/EcsRelationsException.cs b/src/Exceptions/EcsRelationsException.cs
new file mode 100644
index 0000000..685af1b
--- /dev/null
+++ b/src/Exceptions/EcsRelationsException.cs
@@ -0,0 +1,15 @@
+using System;
+
+namespace DCFApixels.DragonECS
+{
+    [Serializable]
+    public class EcsRelationsException : Exception
+    {
+        public EcsRelationsException() { }
+        public EcsRelationsException(string message) : base(EcsConsts.EXCEPTION_MESSAGE_PREFIX + message) { }
+        public EcsRelationsException(string message, Exception inner) : base(EcsConsts.EXCEPTION_MESSAGE_PREFIX + message, inner) { }
+        protected EcsRelationsException(
+            System.Runtime.Serialization.SerializationInfo info, 
+            System.Runtime.Serialization.StreamingContext context) : base(info, context) { }
+    }
+}
diff --git a/src/Interfaces/IEcsTable.cs b/src/Interfaces/IEcsTable.cs
index 90a807b..f96956c 100644
--- a/src/Interfaces/IEcsTable.cs
+++ b/src/Interfaces/IEcsTable.cs
@@ -17,8 +17,9 @@ namespace DCFApixels.DragonECS
         public int GetComponentID<T>();
         public TPool GetPool<TComponent, TPool>() where TComponent : struct where TPool : EcsPoolBase, new();
         public ReadOnlySpan<EcsPoolBase> GetAllPools();
-        public TQuery Where<TQuery>(out TQuery query) where TQuery : EcsQueryBase;
         public TQuery Select<TQuery>() where TQuery : EcsQueryBase;
+        public TQuery Where<TQuery>(out TQuery query) where TQuery : EcsQuery;
+        public TQuery Join<TQuery>(out TQuery query) where TQuery : EcsJoinAttachQuery;
 
         public bool IsMaskCompatible(EcsComponentMask mask, int entityID);
 
diff --git a/src/Pools/EcsAttachPool.cs b/src/Pools/EcsAttachPool.cs
new file mode 100644
index 0000000..1004520
--- /dev/null
+++ b/src/Pools/EcsAttachPool.cs
@@ -0,0 +1,127 @@
+using System;
+using System.Runtime.CompilerServices;
+using Unity.Profiling;
+
+namespace DCFApixels.DragonECS
+{
+    public sealed class EcsAttachPool<T> : EcsPoolBase
+        where T : struct, IEcsAttachComponent
+    {
+        private EcsWorld _source;
+
+        private bool[] _entityFlags;// index = entityID / value = entityFlag;/ value = 0 = no entityID
+        private T[] _items; //sparse
+        private int _count;
+
+        private PoolRunners _poolRunners;
+
+#if (DEBUG && !DISABLE_DEBUG) || !DRAGONECS_NO_SANITIZE_CHECKS
+        private int _sanitizeTargetWorld = -1;
+#endif
+
+        #region Properites
+        public int Count => _count;
+        public int Capacity => _items.Length;
+        public sealed override EcsWorld World => _source;
+        public sealed override Type ComponentType => typeof(T);
+        #endregion
+
+        #region Init
+        protected override void Init(EcsWorld world)
+        {
+            _source = world;
+
+            _entityFlags = new bool[world.Capacity];
+            _items = new T[world.Capacity];
+            _count = 0;
+
+            _poolRunners = new PoolRunners(world.Pipeline);
+        }
+        #endregion
+
+        #region Write/Read/Has/Del
+        private ProfilerMarker _addMark = new ProfilerMarker("EcsPoo.Add");
+        private ProfilerMarker _writeMark = new ProfilerMarker("EcsPoo.Write");
+        private ProfilerMarker _readMark = new ProfilerMarker("EcsPoo.Read");
+        private ProfilerMarker _hasMark = new ProfilerMarker("EcsPoo.Has");
+        private ProfilerMarker _delMark = new ProfilerMarker("EcsPoo.Del");
+        public void Add(int entityID, EcsEntity target)
+        {
+#if (DEBUG && !DISABLE_DEBUG) || !DRAGONECS_NO_SANITIZE_CHECKS
+            if (_sanitizeTargetWorld >= 0 && target.world != _sanitizeTargetWorld)
+            {
+                throw new EcsRelationsException();
+            }
+#endif
+            // using (_addMark.Auto())
+            //  {
+            ref bool entityFlag = ref _entityFlags[entityID];
+            if (entityFlag == false)
+            {
+                entityFlag = true;
+                _count++;
+                _poolRunners.add.OnComponentAdd<T>(entityID);
+            }
+            _poolRunners.write.OnComponentWrite<T>(entityID);
+            _items[entityID].Target = target;
+            // }
+        }
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Set(int entityID, EcsEntity target)
+        {
+#if (DEBUG && !DISABLE_DEBUG) || !DRAGONECS_NO_SANITIZE_CHECKS
+            if (_sanitizeTargetWorld >= 0 && target.world != _sanitizeTargetWorld)
+            {
+                throw new EcsRelationsException();
+            }
+#endif
+            //   using (_writeMark.Auto())
+            _poolRunners.write.OnComponentWrite<T>(entityID);
+            _items[entityID].Target = target;
+        }
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public ref readonly T Read(int entityID)
+        {
+            //  using (_readMark.Auto())
+            return ref _items[entityID];
+        }
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public sealed override bool Has(int entityID)
+        {
+            //  using (_hasMark.Auto())
+            return _entityFlags[entityID];
+        }
+        public void Del(int entityID)
+        {
+            //  using (_delMark.Auto())
+            //   {
+            _entityFlags[entityID] = false;
+            _count--;
+            _poolRunners.del.OnComponentDel<T>(entityID);
+            //   }
+        }
+        #endregion
+
+        #region WorldCallbacks
+        protected override void OnWorldResize(int newSize)
+        {
+            Array.Resize(ref _entityFlags, newSize);
+            Array.Resize(ref _items, newSize);
+        }
+        protected override void OnDestroy() { }
+        #endregion
+    }
+
+    public interface IEcsAttachComponent
+    {
+        public EcsEntity Target { get; set; }
+    }
+    public static class EcsAttachComponentPoolExt
+    {
+        public static EcsAttachPool<TAttachComponent> GetPool<TAttachComponent>(this EcsWorld self)
+            where TAttachComponent : struct, IEcsAttachComponent
+        {
+            return self.GetPool<TAttachComponent, EcsAttachPool<TAttachComponent>>();
+        } 
+    }
+}
diff --git a/src/Pools/EcsNotNullPool.cs b/src/Pools/EcsNotNullPool.cs
index 028b764..d20fc86 100644
--- a/src/Pools/EcsNotNullPool.cs
+++ b/src/Pools/EcsNotNullPool.cs
@@ -5,11 +5,10 @@ using Unity.Profiling;
 namespace DCFApixels.DragonECS
 {
     public sealed class EcsNotNullPool<T> : EcsPoolBase
-        where T : struct
+        where T : struct, INotNullComponent
     {
         private EcsWorld _source;
 
-        private bool[] _entityFlags;// index = entityID / value = entityFlag;/ value = 0 = no entityID
         private T[] _items; //sparse
         private int _count;
 
@@ -28,7 +27,6 @@ namespace DCFApixels.DragonECS
         {
             _source = world;
 
-            _entityFlags = new bool[world.Capacity];
             _items = new T[world.Capacity];
             _count = 0;
 
@@ -37,27 +35,12 @@ namespace DCFApixels.DragonECS
         }
         #endregion
 
-        #region Write/Read/Has/Del
+        #region Write/Read/Has
         private ProfilerMarker _addMark = new ProfilerMarker("EcsPoo.Add");
         private ProfilerMarker _writeMark = new ProfilerMarker("EcsPoo.Write");
         private ProfilerMarker _readMark = new ProfilerMarker("EcsPoo.Read");
         private ProfilerMarker _hasMark = new ProfilerMarker("EcsPoo.Has");
         private ProfilerMarker _delMark = new ProfilerMarker("EcsPoo.Del");
-        public ref T Add(int entityID)
-        {
-            // using (_addMark.Auto())
-            //  {
-            ref bool entityFlag = ref _entityFlags[entityID];
-            if (entityFlag == false)
-            {
-                entityFlag = true;
-                _count++;
-                _poolRunners.add.OnComponentAdd<T>(entityID);
-            }
-            _poolRunners.write.OnComponentWrite<T>(entityID);
-            return ref _items[entityID];
-            // }
-        }
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public ref T Write(int entityID)
         {
@@ -75,24 +58,13 @@ namespace DCFApixels.DragonECS
         public sealed override bool Has(int entityID)
         {
             //  using (_hasMark.Auto())
-            return _entityFlags[entityID];
-        }
-        public void Del(int entityID)
-        {
-            //  using (_delMark.Auto())
-            //   {
-            _componentResetHandler.Reset(ref _items[entityID]);
-            _entityFlags[entityID] = false;
-            _count--;
-            _poolRunners.del.OnComponentDel<T>(entityID);
-            //   }
+            return true;
         }
         #endregion
 
         #region WorldCallbacks
         protected override void OnWorldResize(int newSize)
         {
-            Array.Resize(ref _entityFlags, newSize);
             Array.Resize(ref _items, newSize);
         }
         protected override void OnDestroy() { }
@@ -102,10 +74,10 @@ namespace DCFApixels.DragonECS
     public interface INotNullComponent { }
     public static class EcsNotNullPoolExt
     {
-        public static EcsNotNullPool<TComponent> GetPool<TComponent>(this EcsWorld self)
-            where TComponent : struct, INotNullComponent
+        public static EcsNotNullPool<TNotNullComponent> GetPool<TNotNullComponent>(this EcsWorld self)
+            where TNotNullComponent : struct, INotNullComponent
         {
-            return self.GetPool<TComponent, EcsNotNullPool<TComponent>>();
+            return self.GetPool<TNotNullComponent, EcsNotNullPool<TNotNullComponent>>();
         } 
     }
 }
diff --git a/src/Pools/EcsPool.cs b/src/Pools/EcsPool.cs
index f31c92d..3846b98 100644
--- a/src/Pools/EcsPool.cs
+++ b/src/Pools/EcsPool.cs
@@ -50,7 +50,7 @@ namespace DCFApixels.DragonECS
     }
 
     public sealed class EcsPool<T> : EcsPoolBase
-        where T : struct
+        where T : struct, IEcsComponent
     {
         private EcsWorld _source;
 
diff --git a/src/Pools/EcsRelationPool.cs b/src/Pools/EcsRelationPool.cs
new file mode 100644
index 0000000..164a3d0
--- /dev/null
+++ b/src/Pools/EcsRelationPool.cs
@@ -0,0 +1,134 @@
+using System;
+using System.Runtime.CompilerServices;
+using Unity.Profiling;
+
+namespace DCFApixels.DragonECS
+{
+    public sealed class EcsRelationPool<T> : EcsPoolBase
+        where T : struct, IEcsRelationComponent
+    {
+        private EcsWorld _source;
+
+        private bool[] _entityFlags;// index = entityID / value = entityFlag;/ value = 0 = no entityID
+        private T[] _items; //sparse
+        private int _count;
+
+        private PoolRunners _poolRunners;
+
+#if (DEBUG && !DISABLE_DEBUG) || !DRAGONECS_NO_SANITIZE_CHECKS
+        private int _sanitizeFirstWorld = -1;
+        private int _sanitizeSecondWorld = -1;
+#endif
+
+        #region Properites
+        public int Count => _count;
+        public int Capacity => _items.Length;
+        public sealed override EcsWorld World => _source;
+        public sealed override Type ComponentType => typeof(T);
+        #endregion
+
+        #region Init
+        protected override void Init(EcsWorld world)
+        {
+            _source = world;
+
+            _entityFlags = new bool[world.Capacity];
+            _items = new T[world.Capacity];
+            _count = 0;
+
+            _poolRunners = new PoolRunners(world.Pipeline);
+        }
+        #endregion
+
+        #region Write/Read/Has/Del
+        private ProfilerMarker _addMark = new ProfilerMarker("EcsPoo.Add");
+        private ProfilerMarker _writeMark = new ProfilerMarker("EcsPoo.Write");
+        private ProfilerMarker _readMark = new ProfilerMarker("EcsPoo.Read");
+        private ProfilerMarker _hasMark = new ProfilerMarker("EcsPoo.Has");
+        private ProfilerMarker _delMark = new ProfilerMarker("EcsPoo.Del");
+        public void Add(int entityID, EcsEntity first, EcsEntity second)
+        {
+#if (DEBUG && !DISABLE_DEBUG) || !DRAGONECS_NO_SANITIZE_CHECKS
+            if((_sanitizeFirstWorld >= 0 && first.world != _sanitizeFirstWorld) &&
+                (_sanitizeSecondWorld >= 0 && second.world != _sanitizeSecondWorld))
+            {
+                throw new EcsRelationsException();
+            }
+#endif
+            // using (_addMark.Auto())
+            //  {
+            ref bool entityFlag = ref _entityFlags[entityID];
+            if (entityFlag == false)
+            {
+                entityFlag = true;
+                _count++;
+                _poolRunners.add.OnComponentAdd<T>(entityID);
+            }
+            _poolRunners.write.OnComponentWrite<T>(entityID);
+            _items[entityID].Set(first, second);
+            // }
+        }
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Set(int entityID, EcsEntity first, EcsEntity second)
+        {
+#if (DEBUG && !DISABLE_DEBUG) || !DRAGONECS_NO_SANITIZE_CHECKS
+            if ((_sanitizeFirstWorld >= 0 && first.world != _sanitizeFirstWorld) &&
+                (_sanitizeSecondWorld >= 0 && second.world != _sanitizeSecondWorld))
+            {
+                throw new EcsRelationsException();
+            }
+#endif
+            //   using (_writeMark.Auto())
+            //{
+            _poolRunners.write.OnComponentWrite<T>(entityID);
+                _items[entityID].Set(first, second);
+            //}
+        }
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public ref readonly T Read(int entityID)
+        {
+            //  using (_readMark.Auto())
+            return ref _items[entityID];
+        }
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public sealed override bool Has(int entityID)
+        {
+            //  using (_hasMark.Auto())
+            return _entityFlags[entityID];
+        }
+        public void Del(int entityID)
+        {
+            //  using (_delMark.Auto())
+            //   {
+            _entityFlags[entityID] = false;
+            _count--;
+            _poolRunners.del.OnComponentDel<T>(entityID);
+            //   }
+        }
+        #endregion
+
+        #region WorldCallbacks
+        protected override void OnWorldResize(int newSize)
+        {
+            Array.Resize(ref _entityFlags, newSize);
+            Array.Resize(ref _items, newSize);
+        }
+        protected override void OnDestroy() { }
+        #endregion
+    }
+
+    public interface IEcsRelationComponent
+    {
+        public EcsEntity First { get; set; }
+        public EcsEntity Second { get; set; }
+        public void Set(EcsEntity first, EcsEntity second);
+    }
+    public static class EcsRelationPoolExt
+    {
+        public static EcsRelationPool<TRelationComponent> GetPool<TRelationComponent>(this EcsWorld self)
+            where TRelationComponent : struct, IEcsRelationComponent
+        {
+            return self.GetPool<TRelationComponent, EcsRelationPool<TRelationComponent>>();
+        } 
+    }
+}
diff --git a/src/Pools/EcsSinglePool.cs b/src/Pools/EcsSinglePool.cs
index 7590b98..3f58361 100644
--- a/src/Pools/EcsSinglePool.cs
+++ b/src/Pools/EcsSinglePool.cs
@@ -5,7 +5,7 @@ using Unity.Profiling;
 namespace DCFApixels.DragonECS
 {
     public sealed class EcsSinglePool<T> : EcsPoolBase
-         where T : struct
+         where T : struct, IEcsSingleComponent
     {
         private EcsWorld _source;
 
@@ -93,11 +93,11 @@ namespace DCFApixels.DragonECS
         #endregion
     }
 
-    public interface ISingleComponent { }
+    public interface IEcsSingleComponent { }
     public static class EcsSinglePoolExt
     {
         public static EcsSinglePool<TSingleComponent> GetPool<TSingleComponent>(this EcsWorld self)
-            where TSingleComponent : struct, ISingleComponent
+            where TSingleComponent : struct, IEcsSingleComponent
         {
             return self.GetPool<TSingleComponent, EcsSinglePool<TSingleComponent>>();
         } 
diff --git a/src/Pools/EcsTagPool.cs b/src/Pools/EcsTagPool.cs
index 07698dd..6e93734 100644
--- a/src/Pools/EcsTagPool.cs
+++ b/src/Pools/EcsTagPool.cs
@@ -5,11 +5,11 @@ using Unity.Profiling;
 namespace DCFApixels.DragonECS
 {
     public sealed class EcsTagPool<T> : EcsPoolBase
-        where T : struct
+        where T : struct, IEcsTagComponent
     {
         private EcsWorld _source;
 
-        private int[] _mapping;// index = entityID / value = itemIndex;/ value = 0 = no entityID
+        private bool[] _mapping;// index = entityID / value = itemIndex;/ value = 0 = no entityID
         private int _count;
 
         private PoolRunners _poolRunners;
@@ -25,7 +25,7 @@ namespace DCFApixels.DragonECS
         {
             _source = world;
 
-            _mapping = new int[world.Capacity];
+            _mapping = new bool[world.Capacity];
             _count = 0;
 
             _poolRunners = new PoolRunners(world.Pipeline);
@@ -40,9 +40,10 @@ namespace DCFApixels.DragonECS
         {
             // using (_addMark.Auto())
             //  {
-            if (_mapping[entityID] <= 0)
+            if (_mapping[entityID] == false)
             {
-                _mapping[entityID] = ++_count;
+                _count++;
+                _mapping[entityID] = true;
                 _poolRunners.add.OnComponentAdd<T>(entityID);
             }
             // }
@@ -51,13 +52,13 @@ namespace DCFApixels.DragonECS
         public sealed override bool Has(int entityID)
         {
             //  using (_hasMark.Auto())
-            return _mapping[entityID] > 0;
+            return _mapping[entityID];
         }
         public void Del(int entityID)
         {
             //  using (_delMark.Auto())
             //   {
-            _mapping[entityID] = 0;
+            _mapping[entityID] = false;
             _count--;
             _poolRunners.del.OnComponentDel<T>(entityID);
             //   }