diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..f00ef23
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,10 @@
+# Changelog
+
+## 1.1
+
+Adapting ControlModel to be able to use the full Persistent-Type range and use
+observers instead of baked in functions.
+
+## 1.0
+
+initial version
diff --git a/Jenkinsfile b/Jenkinsfile
index 81d532c..12d359d 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -5,7 +5,7 @@ pipeline {
         VERSION = VersionNumber([
             versionNumberString:
                 '${BUILDS_ALL_TIME}',
-            versionPrefix: '1.0.',
+            versionPrefix: '1.1.',
             worstResultForIncrement: 'SUCCESS'
         ])
     }
diff --git a/README.md b/README.md
index 407c5f9..51c4da4 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # @sapphirecode/modelling
 
-version: 1.0.x
+version: 1.1.x
 
 base classes for controlling data
 
@@ -83,10 +83,13 @@ also extends Persistent.
 
 The method define_properties lets you define the data you will store.
 
-verify is meant to check and modify data.
+before_change allows you to register observers, that are able to cancel changes.
+the registered observers are called with the following parameters: (new_value,
+old_value, property_name). By returning false they can cancel the change that
+was about to happen.
 
-update should be called when data was modified, by default it just calls verify,
-but can also be used to report updates to other components
+register_observer does the same thing, but those observers are not able to
+cancel the change and they are called after the change already happened.
 
 ### Interfaces
 
diff --git a/lib/ControlModel.ts b/lib/ControlModel.ts
index 9ced8b9..fedbdae 100644
--- a/lib/ControlModel.ts
+++ b/lib/ControlModel.ts
@@ -6,43 +6,46 @@
  */
 
 import { Persistent } from './Persistent';
+import { PersistentType, ControlObserver, Observer } from './Types';
 
 export abstract class ControlModel extends Persistent {
-  public constructor (obj?: Record<string, string|number|boolean>) {
+  private _before_change: Record<string, ControlObserver[]> = {};
+  private _observers: Record<string, Observer[]> = {};
+
+  public constructor (obj?: Record<string, PersistentType>) {
     super ();
     this.define_properties ();
-    for (const prop of Object.keys (this.properties)) {
-      if ([
-        'string',
-        'number',
-        'boolean'
-      ].indexOf (this.properties[prop]) < 0) {
-        throw new Error (
-          'property types have to be either string, number or boolean'
-        );
-      }
-    }
-
     if (typeof obj !== 'undefined')
       this.assign_object (obj);
   }
 
-  public to_object (): Record<string, string|number|boolean> {
-    return super.to_object () as Record<string, string|number|boolean>;
-  }
+  public set (key: string, value: PersistentType): void {
+    const prev = this.get (key);
+    if (typeof this._before_change[key] !== 'undefined') {
+      for (const obs of this._before_change[key]) {
+        if (!obs (value, prev, key))
+          return;
+      }
+    }
 
-  public get (key: string): string|number|boolean {
-    return super.get (key) as string|number|boolean;
-  }
-
-  public set (key: string, value: string|number|boolean): void {
     super.set (key, value);
+    if (typeof this._observers[key] !== 'undefined') {
+      for (const obs of this._observers[key])
+        obs (value, prev, key);
+    }
   }
 
-  public update (): void {
-    this.verify ();
+  public before_change (key: string, func: ControlObserver): void {
+    if (typeof this._before_change[key] === 'undefined')
+      this._before_change[key] = [];
+    this._before_change[key].push (func);
+  }
+
+  public register_observer (key: string, func: Observer): void {
+    if (typeof this._observers[key] === 'undefined')
+      this._observers[key] = [];
+    this._observers[key].push (func);
   }
 
-  public abstract verify(): void;
   protected abstract define_properties(): void;
 }
diff --git a/lib/Persistent.ts b/lib/Persistent.ts
index 89d2531..0dba60c 100644
--- a/lib/Persistent.ts
+++ b/lib/Persistent.ts
@@ -7,10 +7,7 @@
 
 import { copy_object } from '@sapphirecode/utilities';
 import { Assignable, Serializable } from './interfaces';
-
-type PersistentTypeString = 'string'|'number'|'boolean'|'array';
-type PersistentPrimitive = string|number|boolean;
-type PersistentType = PersistentPrimitive|PersistentPrimitive[];
+import { PersistentTypeString, PersistentType } from './Types';
 
 export abstract class Persistent implements Assignable, Serializable {
   private _data: Record<string, PersistentType> = {};
diff --git a/lib/Types.ts b/lib/Types.ts
new file mode 100644
index 0000000..c726d94
--- /dev/null
+++ b/lib/Types.ts
@@ -0,0 +1,15 @@
+export type PersistentTypeString = 'string'|'number'|'boolean'|'array';
+export type PersistentPrimitive = string|number|boolean;
+export type PersistentType = PersistentPrimitive|PersistentPrimitive[];
+
+export type Observer = (
+  value: PersistentType,
+   prev: PersistentType,
+   key: string
+) => void;
+
+export type ControlObserver = (
+  value: PersistentType,
+  prev: PersistentType,
+  key: string
+) => boolean;