diff --git a/Extensions/XReferenceExtensions.cs b/Extensions/XReferenceExtensions.cs
new file mode 100644
index 0000000..f9caa8d
--- /dev/null
+++ b/Extensions/XReferenceExtensions.cs
@@ -0,0 +1,176 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using xCommons.Extensions;
+using xDataService.Models;
+
+namespace xDataService.Extensions
+{
+    public static class XReferenceExtensions
+    {
+        /// <summary>
+        /// Converts an XReference<T> to String Representation ...
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="source"></param>
+        /// <param name="splitter"></param>
+        /// <returns></returns>
+        public static string ToXReferenceString<T>(
+            this XReference<T> source,
+            char? splitter = '_'
+        )
+        {
+            //
+            var result = string.Empty;
+
+            //
+            // Normalize Splitter ...
+            if (!splitter.HasValue)
+            {
+                splitter = '_';
+            }
+
+            //
+            if (!source.IsNullOrDefault() && source.Index >= 0 && !source.ReferencedTo.IsNull())
+            {
+                result = $"{source.ProvidedFor}{splitter.Value}{source.ReferencedTo}{splitter.Value}{source.Index}";
+            }
+
+            //
+            return result;
+        }
+
+        /// <summary>
+        /// Parse an String and Extract to XReference<T> if it's Described ...
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="source"></param>
+        /// <param name="splitter"></param>
+        /// <returns></returns>
+        public static XReference<T> FromXReference<T>(
+            this string source,
+            char? splitter = '_'
+        )
+        {
+            //
+            XReference<T> result = null;
+
+            //
+            // Normalize Splitter ...
+            if (!splitter.HasValue)
+            {
+                splitter = '_';
+            }
+
+            //
+            if (!source.IsNullOrEmpty())
+            {
+                //
+                var parts = source.Split(splitter.Value);
+                if (parts.Count() >= 3)
+                {
+                    //
+                    // Parse String Parts ...
+                    result = new XReference<T>
+                    {
+                        Index = (int)Convert.ChangeType(parts[2], typeof(int)),
+                        ReferencedTo = (T)Convert.ChangeType(parts[1], typeof(T)),
+                        ProvidedFor = (string)Convert.ChangeType(parts[0], typeof(string)),
+                    };
+                }
+            }
+
+            //
+            return result;
+        }
+
+        /// <summary>
+        /// Converts a Collection of XReference<T> to it's String Representation ...
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="source"></param>
+        /// <returns></returns>
+        public static string ToXReferenceString<T>(this IEnumerable<XReference<T>> source)
+        {
+            //
+            var result = string.Empty;
+
+            //
+            if (source.IsNull() && source.HasChild())
+            {
+                //
+                var stringList = new List<string>();
+                foreach (var s in source)
+                {
+                    //
+                    var sr = ToXReferenceString(s);
+                    if (!sr.IsNullOrEmpty())
+                    {
+                        stringList.Add(sr);
+                    }
+                }
+
+                //
+                result = stringList.ToListString();
+            }
+
+            //
+            return result;
+        }
+        public static string ToXReferenceString<T>(this ICollection<XReference<T>> source)
+        {
+            //
+            var result = source
+                .AsEnumerable()
+                .ToXReferenceString();
+
+            //
+            return result;
+        }
+        public static string ToXReferenceString<T>(this IList<XReference<T>> source)
+        {
+            //
+            var result = source
+                .AsEnumerable()
+                .ToXReferenceString();
+
+            //
+            return result;
+        }
+
+        /// <summary>
+        /// Parse an string to XReference<T> Collection Representation ...
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="source"></param>
+        /// <returns></returns>
+        public static IList<XReference<T>> ParseXReferenceList<T>(this string source)
+        {
+            //
+            IList<XReference<T>> result = new List<XReference<T>>();
+
+            //
+            if (!source.IsNullOrEmpty())
+            {
+                //
+                var stringList = source.ParseListString<string>();
+                if (!stringList.IsNull() && stringList.HasChild())
+                {
+                    //
+                    foreach (var s in stringList)
+                    {
+                        //
+                        var sr = FromXReference<T>(s);
+                        if (!sr.IsNullOrDefault())
+                        {
+                            result.Add(sr);
+                        }
+                    }
+                }
+            }
+
+            //
+            return result;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Interfaces/IXBaseReferencedProvider.cs b/Interfaces/IXBaseReferencedProvider.cs
new file mode 100644
index 0000000..20b9819
--- /dev/null
+++ b/Interfaces/IXBaseReferencedProvider.cs
@@ -0,0 +1,129 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using xDataService.Models;
+using xModels.Dtos;
+
+namespace xDataService.Interfaces
+{
+    /// <summary>
+    /// in Some Cases we have Entities Which Can Referenced for Specified 
+    /// Provider and Types ...
+    /// this interface Globaly introduce all available Actions for those ...
+    /// 
+    /// TKey: type of Provider Models Keys ...
+    /// TModel: type of Dto which Referenced ...
+    /// </summary>
+    public interface IXBaseReferencedProvider<TModel, TKey>
+    {
+        //
+        #region Props ...
+        /// <summary>
+        /// Provider Identifier ...
+        /// </summary>
+        string Provider { get; }
+        #endregion
+
+        //
+        #region Identifier ...
+        Task<int> LastIndex(TKey providedForId);
+        #endregion
+
+        //
+        #region Referenced Actions ...
+        /// <summary>
+        /// Get Specified Indexed Reference for Specific Provided ID ...
+        /// </summary>
+        /// <param name="providedForId"></param>
+        /// <param name="forIndex"></param>
+        /// <returns></returns>
+        Task<TModel> GetReference(
+            TKey providedForId,
+            int forIndex = 0
+        );
+
+        /// <summary>
+        /// Retrieve all Exists References of Specific Provided ID ...
+        /// </summary>
+        /// <param name="providedForId"></param>
+        /// <returns></returns>
+        Task<IEnumerable<TModel>> GetAllReferences(TKey providedForId);
+
+        /// <summary>
+        /// Retrieve References of Specific Provided ID as Query ...
+        /// </summary>
+        /// <param name="providedForId"></param>
+        /// <returns></returns>
+        Task<XQueryResult<TModel>> QueryReferences(
+            XQuery query,
+            TKey providedForId
+        );
+
+        /// <summary>
+        /// Add Reference a Model to Specific Provided ID ...
+        /// </summary>
+        /// <param name="model"></param>
+        /// <param name="providedForId"></param>
+        /// <param name="forIndex"></param>
+        /// <param name="connectionId"></param>
+        /// <returns></returns>
+        Task<bool> AddReference(
+            TModel model,
+            TKey providedForId,
+            int forIndex = 0,
+            string connectionId = null
+        );
+
+        /// <summary>
+        /// Add Reference a Model to Specific XRefence<TKey> ...
+        /// </summary>
+        /// <param name="model"></param>
+        /// <param name="reference"></param>
+        /// <param name="connectionId"></param>
+        /// <returns></returns>
+        Task<bool> AddReference(
+            TModel model,
+            XReference<TKey> reference,
+            string connectionId = null
+        );
+
+        /// <summary>
+        /// Remove Reference a Model for Specific Provided ID ...
+        /// </summary>
+        /// <param name="model"></param>
+        /// <param name="providedForId"></param>
+        /// <param name="forIndex">if null, removes all</param>
+        /// <param name="connectionId"></param>
+        /// <returns></returns>
+        Task<bool> RemoveReference(
+            TModel model,
+            TKey providedForId,
+            int? forIndex = null,
+            string connectionId = null
+        );
+
+        /// <summary>
+        /// Remove Reference a Model for Specific XRefence<TKey> ...
+        /// </summary>
+        /// <param name="model"></param>
+        /// <param name="providedForId"></param>
+        /// <param name="connectionId"></param>
+        /// <returns></returns>
+        Task<bool> RemoveReference(
+            TModel model,
+            XReference<TKey> reference,
+            string connectionId = null
+        );
+
+        /// <summary>
+        /// Remove All References to Specified Key ...
+        /// </summary>
+        /// <param name="providedForId"></param>
+        /// <param name="connectionId"></param>
+        /// <returns></returns>
+        Task<bool> RemoveReferences(
+            TKey providedForId,
+            string connectionId = null
+        );
+        #endregion
+    }
+}
\ No newline at end of file
diff --git a/Models/XReference.cs b/Models/XReference.cs
new file mode 100644
index 0000000..037417d
--- /dev/null
+++ b/Models/XReference.cs
@@ -0,0 +1,9 @@
+namespace xDataService.Models
+{
+    public class XReference<T>
+    {
+        public int Index { get; set; }
+        public T ReferencedTo { get; set; }
+        public string ProvidedFor { get; set; }
+    }
+}
\ No newline at end of file