diff --git a/lib/interfaces/Assignable.ts b/lib/interfaces/Assignable.ts
index f9f9ab9..5d22e9f 100644
--- a/lib/interfaces/Assignable.ts
+++ b/lib/interfaces/Assignable.ts
@@ -1,11 +1,22 @@
-export abstract class Assignable {
-  protected data: Record<string, unknown> = {};
+export interface Assignable {
+  assign (a: Assignable): void;
+  assign_to (a: Assignable): void;
+}
+
+export abstract class Persistent {
+  private data: Record<string, unknown> = {};
+  private properties: Record<string, string>;
+
+  public constructor() {
+    this.properties = this.define_properties();
+  }
+
+  public abstract define_properties(): Record<string, string>;
 
   public assign (da: Assignable): void {
     this.assign_object (da.get_data ());
   }
 
-
   public assign_to (da: Assignable): void {
     da.assign (this);
   }
@@ -18,4 +29,6 @@ export abstract class Assignable {
   public get_data (): Record<string, unknown> {
     return this.data;
   }
+
+  wip
 }