diff --git a/models/core/src/security.ts b/models/core/src/security.ts
index 3d1d1acf27..a2588a9775 100644
--- a/models/core/src/security.ts
+++ b/models/core/src/security.ts
@@ -13,10 +13,10 @@
 // limitations under the License.
 //
 
-import type { IntlString } from '@anticrm/platform'
-import type { Account, Arr, Ref, Space, Domain, State } from '@anticrm/core'
+import type { Account, Arr, Domain, Ref, Space, State } from '@anticrm/core'
 import { DOMAIN_MODEL } from '@anticrm/core'
-import { Model, Prop, TypeState, TypeString } from '@anticrm/model'
+import { Implements, Model, Prop, TypeState, TypeString } from '@anticrm/model'
+import type { IntlString } from '@anticrm/platform'
 import core from './component'
 import { TDoc } from './core'
 
@@ -47,7 +47,7 @@ export class TState extends TDoc implements State {
   color!: string
 }
 
-@Model(core.class.DocWithState, core.class.AttachedDoc)
+@Implements(core.interface.DocWithState)
 export class TDocWithState extends TDoc {
   @Prop(TypeState(), 'State' as IntlString)
   state!: Ref<State>
diff --git a/models/recruit/src/index.ts b/models/recruit/src/index.ts
index 6e43ac1f6b..880c18f7dd 100644
--- a/models/recruit/src/index.ts
+++ b/models/recruit/src/index.ts
@@ -13,20 +13,18 @@
 // limitations under the License.
 //
 
-import type { IntlString } from '@anticrm/platform'
-import { Builder, Model, UX, Prop, TypeString, TypeBoolean } from '@anticrm/model'
-import type { Ref, FindOptions, Doc, Domain, Class } from '@anticrm/core'
-import core, { TSpace, TSpaceWithStates, TDocWithState } from '@anticrm/model-core'
-import type { Vacancy, Candidates, Candidate, Applicant } from '@anticrm/recruit'
 import activity from '@anticrm/activity'
 import type { Employee } from '@anticrm/contact'
-
-import workbench from '@anticrm/model-workbench'
-
-import view from '@anticrm/model-view'
-import contact, { TPerson } from '@anticrm/model-contact'
-import recruit from './plugin'
+import type { Doc, Domain, FindOptions, Ref } from '@anticrm/core'
+import { Builder, Model, Prop, TypeBoolean, TypeString, UX } from '@anticrm/model'
 import chunter from '@anticrm/model-chunter'
+import contact, { TPerson } from '@anticrm/model-contact'
+import core, { TAttachedDoc, TDocWithState, TSpace, TSpaceWithStates } from '@anticrm/model-core'
+import view from '@anticrm/model-view'
+import workbench from '@anticrm/model-workbench'
+import type { IntlString } from '@anticrm/platform'
+import type { Applicant, Candidate, Candidates, Vacancy } from '@anticrm/recruit'
+import recruit from './plugin'
 
 export const DOMAIN_RECRUIT = 'recruit' as Domain
 
@@ -63,14 +61,12 @@ export class TCandidate extends TPerson implements Candidate {
   source?: string
 }
 
-@Model(recruit.class.Applicant, core.class.DocWithState, DOMAIN_RECRUIT)
+@Model(recruit.class.Applicant, core.class.AttachedDoc, DOMAIN_RECRUIT, [core.interface.DocWithState])
 @UX('Application' as IntlString, recruit.icon.RecruitApplication, 'APP' as IntlString)
-export class TApplicant extends TDocWithState implements Applicant {
+export class TApplicant extends TAttachedDoc implements Applicant {
+  // We need to declare, to provide property with label
   @Prop(TypeString(), 'Candidate' as IntlString)
-  attachedTo!: Ref<Candidate>
-
-  attachedToClass!: Ref<Class<Candidate>>
-  collection!: string
+  declare attachedTo: Ref<Candidate>
 
   @Prop(TypeString(), 'Attachments' as IntlString)
   attachments?: number
@@ -80,6 +76,10 @@ export class TApplicant extends TDocWithState implements Applicant {
 
   @Prop(TypeString(), 'Assigned recruiter' as IntlString)
   employee!: Ref<Employee>
+
+  // We need this two to make typescript happy.
+  declare state: TDocWithState['state']
+  declare number: TDocWithState['number']
 }
 
 export function createModel (builder: Builder): void {
diff --git a/packages/core/src/__tests__/hierarchy.test.ts b/packages/core/src/__tests__/hierarchy.test.ts
index ce26dbad65..d4f6605b63 100644
--- a/packages/core/src/__tests__/hierarchy.test.ts
+++ b/packages/core/src/__tests__/hierarchy.test.ts
@@ -17,30 +17,45 @@ import type { Class, Doc, Obj, Ref } from '../classes'
 import type { TxCreateDoc } from '../tx'
 import core from '../component'
 import { Hierarchy } from '../hierarchy'
-import { genMinModel } from './minmodel'
+import { genMinModel, test } from './minmodel'
 
 const txes = genMinModel()
 
+function prepare (): Hierarchy {
+  const hierarchy = new Hierarchy()
+  for (const tx of txes) hierarchy.tx(tx)
+  return hierarchy
+}
+
 describe('hierarchy', () => {
   it('should build hierarchy', async () => {
-    const hierarchy = new Hierarchy()
-    for (const tx of txes) hierarchy.tx(tx)
+    const hierarchy = prepare()
     const ancestors = hierarchy.getAncestors(core.class.TxCreateDoc)
     expect(ancestors).toContain(core.class.Tx)
   })
 
   it('isDerived', async () => {
-    const hierarchy = new Hierarchy()
-    for (const tx of txes) hierarchy.tx(tx)
+    const hierarchy = prepare()
     const derived = hierarchy.isDerived(core.class.Space, core.class.Doc)
     expect(derived).toBeTruthy()
     const notDerived = hierarchy.isDerived(core.class.Space, core.class.Class)
     expect(notDerived).not.toBeTruthy()
   })
 
+  it('isImplements', async () => {
+    const hierarchy = prepare()
+    let isImplements = hierarchy.isImplements(test.class.Task, core.interface.DocWithState)
+    expect(isImplements).toBeTruthy()
+
+    isImplements = hierarchy.isImplements(test.class.TaskCheckItem, core.interface.DocWithState)
+    expect(isImplements).toBeTruthy()
+
+    const notImplements = hierarchy.isImplements(core.class.Space, core.interface.DocWithState)
+    expect(notImplements).not.toBeTruthy()
+  })
+
   it('getClass', async () => {
-    const hierarchy = new Hierarchy()
-    for (const tx of txes) hierarchy.tx(tx)
+    const hierarchy = prepare()
     const data = hierarchy.getClass(core.class.TxCreateDoc)
     expect(data).toMatchObject((txes.find((p) => p.objectId === core.class.TxCreateDoc) as TxCreateDoc<Doc>).attributes)
     const notExistClass = 'class:test.MyClass' as Ref<Class<Obj>>
@@ -48,8 +63,7 @@ describe('hierarchy', () => {
   })
 
   it('getDomain', async () => {
-    const hierarchy = new Hierarchy()
-    for (const tx of txes) hierarchy.tx(tx)
+    const hierarchy = prepare()
     const txDomain = hierarchy.getDomain(core.class.TxCreateDoc)
     expect(txDomain).toBe('tx')
     const modelDomain = hierarchy.getDomain(core.class.Class)
diff --git a/packages/core/src/__tests__/minmodel.ts b/packages/core/src/__tests__/minmodel.ts
index 3ddee25128..89ed7d8f2f 100644
--- a/packages/core/src/__tests__/minmodel.ts
+++ b/packages/core/src/__tests__/minmodel.ts
@@ -15,7 +15,8 @@
 
 import type { IntlString, Plugin } from '@anticrm/platform'
 import { plugin } from '@anticrm/platform'
-import type { Arr, Class, Data, Doc, Mixin, Obj, Ref } from '../classes'
+import { DocWithState } from '..'
+import type { Arr, Class, Data, Doc, Interface, Mixin, Obj, Ref } from '../classes'
 import { AttachedDoc, ClassifierKind, DOMAIN_MODEL } from '../classes'
 import core from '../component'
 import type { TxCreateDoc, TxCUD } from '../tx'
@@ -27,6 +28,10 @@ function createClass (_class: Ref<Class<Obj>>, attributes: Data<Class<Obj>>): Tx
   return txFactory.createTxCreateDoc(core.class.Class, core.space.Model, attributes, _class)
 }
 
+function createInterface (_interface: Ref<Interface<Doc>>, attributes: Data<Interface<Doc>>): TxCreateDoc<Doc> {
+  return txFactory.createTxCreateDoc(core.class.Interface, core.space.Model, attributes, _interface)
+}
+
 export function createDoc<T extends Doc> (_class: Ref<Class<T>>, attributes: Data<T>): TxCreateDoc<Doc> {
   return txFactory.createTxCreateDoc(_class, core.space.Model, attributes)
 }
@@ -39,12 +44,26 @@ export interface AttachedComment extends AttachedDoc {
   message: string
 }
 
+export interface Task extends Doc, DocWithState {
+  name: string
+}
+
+export interface TaskCheckItem extends AttachedDoc, DocWithState {
+  name: string
+  complete: boolean
+}
+
 export const test = plugin('test' as Plugin, {
   mixin: {
     TestMixin: '' as Ref<Mixin<TestMixin>>
   },
   class: {
+    Task: '' as Ref<Class<Task>>,
+    TaskCheckItem: '' as Ref<Class<TaskCheckItem>>,
     TestComment: '' as Ref<Class<AttachedComment>>
+  },
+  interface: {
+    DummyDocWithState: '' as Ref<Interface<DocWithState>>
   }
 })
 
@@ -59,9 +78,12 @@ export function genMinModel (): TxCUD<Doc>[] {
   txes.push(createClass(core.class.Doc, { label: 'Doc' as IntlString, extends: core.class.Obj, kind: ClassifierKind.CLASS }))
   txes.push(createClass(core.class.AttachedDoc, { label: 'AttachedDoc' as IntlString, extends: core.class.Doc, kind: ClassifierKind.MIXIN }))
   txes.push(createClass(core.class.Class, { label: 'Class' as IntlString, extends: core.class.Doc, kind: ClassifierKind.CLASS, domain: DOMAIN_MODEL }))
+  txes.push(createClass(core.class.Interface, { label: 'Interface' as IntlString, extends: core.class.Doc, kind: ClassifierKind.CLASS }))
   txes.push(createClass(core.class.Space, { label: 'Space' as IntlString, extends: core.class.Doc, kind: ClassifierKind.CLASS, domain: DOMAIN_MODEL }))
   txes.push(createClass(core.class.Account, { label: 'Account' as IntlString, extends: core.class.Doc, kind: ClassifierKind.CLASS, domain: DOMAIN_MODEL }))
 
+  txes.push(createInterface(core.interface.DocWithState, { label: 'DocWithState' as IntlString, extends: [], kind: ClassifierKind.INTERFACE }))
+
   txes.push(createClass(core.class.Tx, { label: 'Tx' as IntlString, extends: core.class.Doc, kind: ClassifierKind.CLASS, domain: DOMAIN_TX }))
   txes.push(createClass(core.class.TxCUD, { label: 'TxCUD' as IntlString, extends: core.class.Tx, kind: ClassifierKind.CLASS, domain: DOMAIN_TX }))
   txes.push(createClass(core.class.TxCreateDoc, { label: 'TxCreateDoc' as IntlString, extends: core.class.TxCUD, kind: ClassifierKind.CLASS }))
@@ -71,7 +93,10 @@ export function genMinModel (): TxCUD<Doc>[] {
 
   txes.push(createClass(test.mixin.TestMixin, { label: 'TestMixin' as IntlString, extends: core.class.Doc, kind: ClassifierKind.MIXIN }))
 
+  txes.push(createInterface(test.interface.DummyDocWithState, { label: 'DummyDocWithState' as IntlString, extends: [core.interface.DocWithState], kind: ClassifierKind.INTERFACE }))
   txes.push(createClass(test.class.TestComment, { label: 'TestComment' as IntlString, extends: core.class.AttachedDoc, kind: ClassifierKind.CLASS }))
+  txes.push(createClass(test.class.Task, { label: 'Task' as IntlString, extends: core.class.Doc, implements: [test.interface.DummyDocWithState], kind: ClassifierKind.CLASS }))
+  txes.push(createClass(test.class.TaskCheckItem, { label: 'Task' as IntlString, extends: core.class.AttachedDoc, implements: [core.interface.DocWithState], kind: ClassifierKind.CLASS }))
 
   txes.push(
     createDoc(core.class.Space, {
diff --git a/packages/core/src/classes.ts b/packages/core/src/classes.ts
index c58da7d427..046bdf33b6 100644
--- a/packages/core/src/classes.ts
+++ b/packages/core/src/classes.ts
@@ -103,6 +103,7 @@ export type AnyAttribute = Attribute<Type<any>>
  */
 export enum ClassifierKind {
   CLASS,
+  INTERFACE,
   MIXIN
 }
 
@@ -118,12 +119,21 @@ export interface Classifier extends Doc, UXObject {
  */
 export type Domain = string & { __domain: true }
 
+/**
+ * @public
+ */
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+export interface Interface<T extends Doc> extends Classifier {
+  extends?: Ref<Interface<Doc>>[]
+}
+
 /**
  * @public
  */
 // eslint-disable-next-line @typescript-eslint/no-unused-vars
 export interface Class<T extends Obj> extends Classifier {
   extends?: Ref<Class<Obj>>
+  implements?: Ref<Interface<Doc>>[]
   domain?: Domain
   shortLabel?: IntlString
 }
diff --git a/packages/core/src/component.ts b/packages/core/src/component.ts
index c700f164ec..1b8cff025c 100644
--- a/packages/core/src/component.ts
+++ b/packages/core/src/component.ts
@@ -14,8 +14,8 @@
 //
 import type { Plugin, StatusCode } from '@anticrm/platform'
 import { plugin } from '@anticrm/platform'
-import type { Account, Class, Doc, Obj, Ref, Space, AnyAttribute, State, Type, PropertyType, SpaceWithStates, Timestamp, DocWithState, AttachedDoc } from './classes'
-import type { Tx, TxCollectionCUD, TxBulkWrite, TxCreateDoc, TxCUD, TxMixin, TxPutBag, TxRemoveDoc, TxUpdateDoc } from './tx'
+import type { Account, AnyAttribute, AttachedDoc, Class, Doc, DocWithState, Interface, Obj, PropertyType, Ref, Space, SpaceWithStates, State, Timestamp, Type } from './classes'
+import type { Tx, TxBulkWrite, TxCollectionCUD, TxCreateDoc, TxCUD, TxMixin, TxPutBag, TxRemoveDoc, TxUpdateDoc } from './tx'
 
 /**
  * @public
@@ -28,6 +28,7 @@ export default plugin(coreId, {
     Doc: '' as Ref<Class<Doc>>,
     AttachedDoc: '' as Ref<Class<AttachedDoc>>,
     Class: '' as Ref<Class<Class<Obj>>>,
+    Interface: '' as Ref<Class<Interface<Doc>>>,
     Attribute: '' as Ref<Class<AnyAttribute>>,
     Tx: '' as Ref<Class<Tx>>,
     TxBulkWrite: '' as Ref<Class<TxBulkWrite>>,
@@ -40,7 +41,6 @@ export default plugin(coreId, {
     TxPutBag: '' as Ref<Class<TxPutBag<PropertyType>>>,
     Space: '' as Ref<Class<Space>>,
     SpaceWithStates: '' as Ref<Class<SpaceWithStates>>,
-    DocWithState: '' as Ref<Class<DocWithState>>,
     Account: '' as Ref<Class<Account>>,
     State: '' as Ref<Class<State>>,
     TypeString: '' as Ref<Class<Type<string>>>,
@@ -48,6 +48,9 @@ export default plugin(coreId, {
     TypeTimestamp: '' as Ref<Class<Type<Timestamp>>>,
     Bag: '' as Ref<Class<Type<Record<string, PropertyType>>>>
   },
+  interface: {
+    DocWithState: '' as Ref<Interface<DocWithState>>
+  },
   space: {
     Tx: '' as Ref<Space>,
     Model: '' as Ref<Space>
diff --git a/packages/core/src/hierarchy.ts b/packages/core/src/hierarchy.ts
index 321b617322..7820cf218a 100644
--- a/packages/core/src/hierarchy.ts
+++ b/packages/core/src/hierarchy.ts
@@ -13,20 +13,20 @@
 // limitations under the License.
 //
 
-import type { Ref, Class, Obj, Domain, Mixin, Doc, AnyAttribute } from './classes'
+import type { AnyAttribute, Class, Classifier, Doc, Domain, Interface, Mixin, Obj, Ref } from './classes'
 import { ClassifierKind } from './classes'
-import { Tx, TxCreateDoc, TxMixin, TxProcessor } from './tx'
-
 import core from './component'
+import type { Tx, TxCreateDoc, TxMixin } from './tx'
+import { TxProcessor } from './tx'
 
 /**
  * @public
  */
 export class Hierarchy {
-  private readonly classes = new Map<Ref<Class<Obj>>, Class<Obj>>()
-  private readonly attributes = new Map<Ref<Class<Obj>>, Map<string, AnyAttribute>>()
-  private readonly descendants = new Map<Ref<Class<Obj>>, Ref<Class<Obj>>[]>()
-  private readonly ancestors = new Map<Ref<Class<Obj>>, Ref<Class<Obj>>[]>()
+  private readonly classifiers = new Map<Ref<Classifier>, Classifier>()
+  private readonly attributes = new Map<Ref<Classifier>, Map<string, AnyAttribute>>()
+  private readonly descendants = new Map<Ref<Classifier>, Ref<Classifier>[]>()
+  private readonly ancestors = new Map<Ref<Classifier>, Ref<Classifier>[]>()
   private readonly proxies = new Map<Ref<Mixin<Doc>>, ProxyHandler<Doc>>()
 
   private createMixinProxyHandler (mixin: Ref<Mixin<Doc>>): ProxyHandler<Doc> {
@@ -36,7 +36,9 @@ export class Hierarchy {
     return {
       get (target: any, property: string, receiver: any): any {
         const value = target[mixin]?.[property]
-        if (value === undefined) { return (ancestorProxy !== null) ? ancestorProxy.get?.(target, property, receiver) : target[property] }
+        if (value === undefined) {
+          return ancestorProxy !== null ? ancestorProxy.get?.(target, property, receiver) : target[property]
+        }
         return value
       }
     }
@@ -56,7 +58,7 @@ export class Hierarchy {
     return new Proxy(doc, this.getMixinProxyHandler(mixin)) as M
   }
 
-  getAncestors (_class: Ref<Class<Obj>>): Ref<Class<Obj>>[] {
+  getAncestors (_class: Ref<Classifier>): Ref<Classifier>[] {
     const result = this.ancestors.get(_class)
     if (result === undefined) {
       throw new Error('ancestors not found: ' + _class)
@@ -65,24 +67,39 @@ export class Hierarchy {
   }
 
   getClass (_class: Ref<Class<Obj>>): Class<Obj> {
-    const data = this.classes.get(_class)
-    if (data === undefined) {
+    const data = this.classifiers.get(_class)
+    if (data === undefined || this.isInterface(data)) {
       throw new Error('class not found: ' + _class)
     }
     return data
   }
 
+  getInterface (_interface: Ref<Interface<Doc>>): Interface<Doc> {
+    const data = this.classifiers.get(_interface)
+    if (data === undefined || !this.isInterface(data)) {
+      throw new Error('interface not found: ' + _interface)
+    }
+    return data
+  }
+
   getDomain (_class: Ref<Class<Obj>>): Domain {
     const klazz = this.getClass(_class)
     if (klazz.domain !== undefined) {
       return klazz.domain
     }
-    if (klazz.extends !== undefined) {
-      const domain = this.getDomain(klazz.extends)
-      klazz.domain = domain
-      return domain
+    klazz.domain = this.findDomain(klazz)
+    return klazz.domain
+  }
+
+  private findDomain (klazz: Class<Doc>): Domain {
+    let _klazz = klazz
+    while (_klazz.extends !== undefined) {
+      _klazz = this.getClass(_klazz.extends)
+      if (_klazz.domain !== undefined) {
+        return _klazz.domain
+      }
     }
-    throw new Error('domain not found: ' + _class)
+    throw new Error(`domain not found: ${klazz._id} `)
   }
 
   tx (tx: Tx): void {
@@ -96,10 +113,9 @@ export class Hierarchy {
   }
 
   private txCreateDoc (tx: TxCreateDoc<Doc>): void {
-    if (tx.objectClass === core.class.Class) {
-      const createTx = tx as TxCreateDoc<Class<Obj>>
-      const _id = createTx.objectId
-      this.classes.set(_id, TxProcessor.createDoc2Doc(createTx))
+    if (tx.objectClass === core.class.Class || tx.objectClass === core.class.Interface) {
+      const _id = tx.objectId as Ref<Classifier>
+      this.classifiers.set(_id, TxProcessor.createDoc2Doc(tx as TxCreateDoc<Classifier>))
       this.addAncestors(_id)
       this.addDescendant(_id)
     } else if (tx.objectClass === core.class.Attribute) {
@@ -115,12 +131,48 @@ export class Hierarchy {
     }
   }
 
+  /**
+   * Check if passed _class is derived from `from` class.
+   * It will iterave over parents.
+   */
   isDerived<T extends Obj>(_class: Ref<Class<T>>, from: Ref<Class<T>>): boolean {
-    let cl: Ref<Class<Obj>> | undefined = _class
+    let cl: Ref<Class<T>> | undefined = _class
     while (cl !== undefined) {
       if (cl === from) return true
-      const attrs = this.classes.get(cl)
-      cl = attrs?.extends
+      cl = this.getClass(cl).extends
+    }
+    return false
+  }
+
+  /**
+   * Check if passed _class implements passed interfaces `from`.
+   * It will check for class parents and they interfaces.
+   */
+  isImplements<T extends Doc>(_class: Ref<Class<T>>, from: Ref<Interface<T>>): boolean {
+    let cl: Ref<Class<T>> | undefined = _class
+    while (cl !== undefined) {
+      const klazz = this.getClass(cl)
+      if (this.isExtends(klazz.implements ?? [], from)) {
+        return true
+      }
+      cl = klazz.extends
+    }
+    return false
+  }
+
+  /**
+   * Check if interface is extends passed interface.
+   */
+  private isExtends<T extends Doc>(extendsOrImplements: Ref<Interface<Doc>>[], from: Ref<Interface<T>>): boolean {
+    const result: Ref<Interface<Doc>>[] = []
+    const toVisit = extendsOrImplements
+    while (toVisit.length > 0) {
+      const ref = toVisit.shift() as Ref<Interface<Doc>>
+      if (ref === from) {
+        return true
+      }
+      addIf(result, ref)
+      toVisit.push(...this.ancestorsOf(ref))
     }
     return false
   }
@@ -133,7 +185,7 @@ export class Hierarchy {
     return data
   }
 
-  private addDescendant<T extends Obj>(_class: Ref<Class<T>>): void {
+  private addDescendant (_class: Ref<Classifier>): void {
     const hierarchy = this.getAncestors(_class)
     for (const cls of hierarchy) {
       const list = this.descendants.get(cls)
@@ -145,20 +197,50 @@ export class Hierarchy {
     }
   }
 
-  private addAncestors<T extends Obj>(_class: Ref<Class<T>>): void {
-    let cl: Ref<Class<Obj>> | undefined = _class
-    while (cl !== undefined) {
-      const list = this.ancestors.get(_class)
-      if (list === undefined) {
-        this.ancestors.set(_class, [cl])
-      } else {
-        list.push(cl)
+  private addAncestors (_class: Ref<Classifier>): void {
+    const cl: Ref<Classifier>[] = [_class]
+    const visited = new Set<Ref<Classifier>>()
+    while (cl.length > 0) {
+      const classifier = cl.shift() as Ref<Classifier>
+      if (addNew(visited, classifier)) {
+        const list = this.ancestors.get(_class)
+        if (list === undefined) {
+          this.ancestors.set(_class, [classifier])
+        } else {
+          addIf(list, classifier)
+        }
+        cl.push(...this.ancestorsOf(classifier))
       }
-      const attrs = this.classes.get(cl)
-      cl = attrs?.extends
     }
   }
 
+  /**
+   * Return extends and implemnets as combined list of references
+   */
+  private ancestorsOf (classifier: Ref<Classifier>): Ref<Classifier>[] {
+    const attrs = this.classifiers.get(classifier)
+    const result: Ref<Classifier>[] = []
+    if (this.isClass(attrs)) {
+      const cls = attrs as Class<Doc>
+      if (cls.extends !== undefined) {
+        result.push(cls.extends)
+      }
+      result.push(...(cls.implements ?? []))
+    }
+    if (this.isInterface(attrs)) {
+      result.push(...((attrs as Interface<Doc>).extends ?? []))
+    }
+    return result
+  }
+
+  private isClass (attrs?: Classifier): boolean {
+    return attrs?.kind === ClassifierKind.CLASS
+  }
+
+  private isInterface (attrs?: Classifier): boolean {
+    return attrs?.kind === ClassifierKind.INTERFACE
+  }
+
   private addAttribute (attribute: AnyAttribute): void {
     const _class = attribute.attributeOf
     let attributes = this.attributes.get(_class)
@@ -169,7 +251,7 @@ export class Hierarchy {
     attributes.set(attribute.name, attribute)
   }
 
-  getAllAttributes (clazz: Ref<Class<Obj>>): Map<string, AnyAttribute> {
+  getAllAttributes (clazz: Ref<Classifier>): Map<string, AnyAttribute> {
     const result = new Map<string, AnyAttribute>()
     const ancestors = this.getAncestors(clazz)
 
@@ -185,16 +267,41 @@ export class Hierarchy {
     return result
   }
 
-  getAttribute (_class: Ref<Class<Obj>>, name: string): AnyAttribute {
-    const attribute = this.attributes.get(_class)?.get(name)
-    if (attribute === undefined) {
-      const clazz = this.getClass(_class)
-      if (clazz.extends !== undefined) {
-        return this.getAttribute(clazz.extends, name)
-      } else {
-        throw new Error('attribute not found: ' + name)
+  getAttribute (classifier: Ref<Classifier>, name: string): AnyAttribute {
+    const attr = this.findAttribute(classifier, name)
+    if (attr === undefined) {
+      throw new Error('attribute not found: ' + name)
+    }
+    return attr
+  }
+
+  private findAttribute (classifier: Ref<Classifier>, name: string): AnyAttribute | undefined {
+    const list = [classifier]
+    const visited = new Set<Ref<Classifier>>()
+    while (list.length > 0) {
+      const cl = list.shift() as Ref<Classifier>
+      if (addNew(visited, cl)) {
+        const attribute = this.attributes.get(cl)?.get(name)
+        if (attribute !== undefined) {
+          return attribute
+        }
+        // Check ancestorsOf
+        list.push(...this.ancestorsOf(cl))
       }
     }
-    return attribute
+  }
+}
+
+function addNew<T> (val: Set<T>, value: T): boolean {
+  if (val.has(value)) {
+    return false
+  }
+  val.add(value)
+  return true
+}
+
+function addIf<T> (array: T[], value: T): void {
+  if (!array.includes(value)) {
+    array.push(value)
   }
 }
diff --git a/packages/model/src/dsl.ts b/packages/model/src/dsl.ts
index ab4797afb1..757ef455e7 100644
--- a/packages/model/src/dsl.ts
+++ b/packages/model/src/dsl.ts
@@ -15,7 +15,7 @@
 
 import core, {
   Account,
-  Attribute, Class, ClassifierKind, Data, Doc, Domain, ExtendedAttributes, generateId, IndexKind, Mixin as IMixin, Obj, PropertyType, Ref, Space, Tx, TxCreateDoc, TxFactory, TxProcessor, Type
+  Attribute, Class, Classifier, ClassifierKind, Data, Doc, Domain, ExtendedAttributes, generateId, IndexKind, Interface, Mixin as IMixin, Obj, PropertyType, Ref, Space, Tx, TxCreateDoc, TxFactory, TxProcessor, Type
 } from '@anticrm/core'
 import type { Asset, IntlString } from '@anticrm/platform'
 import toposort from 'toposort'
@@ -38,8 +38,9 @@ function getIndex (target: any, property: string): IndexKind | undefined {
 }
 
 interface ClassTxes {
-  _id: Ref<Class<Obj>>
+  _id: Ref<Classifier>
   extends?: Ref<Class<Obj>>
+  implements?: Ref<Interface<Doc>>[]
   domain?: Domain
   label: IntlString
   icon?: Asset
@@ -105,17 +106,34 @@ export function Index (kind: IndexKind) {
 export function Model<T extends Obj> (
   _class: Ref<Class<T>>,
   _extends: Ref<Class<Obj>>,
-  domain?: Domain
+  domain?: Domain,
+  _implements?: Ref<Interface<Doc>>[]
 ) {
   return function classDecorator<C extends new () => T> (constructor: C): void {
     const txes = getTxes(constructor.prototype)
     txes._id = _class
     txes.extends = _class !== core.class.Obj ? _extends : undefined
+    txes.implements = _implements
     txes.domain = domain
     txes.kind = ClassifierKind.CLASS
   }
 }
 
+/**
+ * @public
+ */
+export function Implements<T extends Doc> (
+  _interface: Ref<Interface<T>>,
+  _extends?: Ref<Interface<Doc>>[]
+) {
+  return function classDecorator<C extends new () => T> (constructor: C): void {
+    const txes = getTxes(constructor.prototype)
+    txes._id = _interface
+    txes.implements = _extends
+    txes.kind = ClassifierKind.INTERFACE
+  }
+}
+
 /**
  * @public
  */
@@ -166,13 +184,13 @@ const txFactory = new TxFactory(core.account.System)
 
 function _generateTx (tx: ClassTxes): Tx[] {
   const objectId = tx._id
-  const createTx = txFactory.createTxCreateDoc(
+  const createTx = txFactory.createTxCreateDoc<Doc>(
     core.class.Class,
     core.space.Model,
     {
-      domain: tx.domain,
-      kind: ClassifierKind.CLASS,
-      extends: tx.extends,
+      ...(tx.domain !== undefined ? { domain: tx.domain } : {}),
+      kind: tx.kind,
+      ...(tx.kind === ClassifierKind.INTERFACE ? { extends: tx.implements } : { extends: tx.extends, implements: tx.implements }),
       label: tx.label,
       icon: tx.icon,
       shortLabel: tx.shortLabel
diff --git a/server/view-resources/src/index.ts b/server/view-resources/src/index.ts
index be7b009c95..62eff8c697 100644
--- a/server/view-resources/src/index.ts
+++ b/server/view-resources/src/index.ts
@@ -30,7 +30,7 @@ export async function OnDocWithState (tx: Tx, txFactory: TxFactory, findAll: Fin
 
   if (hierarchy.isDerived(tx._class, core.class.TxCreateDoc)) {
     const createTx = tx as TxCreateDoc<DocWithState>
-    if (hierarchy.isDerived(createTx.objectClass, core.class.DocWithState)) {
+    if (hierarchy.isImplements(createTx.objectClass, core.interface.DocWithState)) {
       const state = (await (findAll as FindAll<State>)(core.class.State, { space: createTx.objectSpace }))[0] // TODO: make FindAll generic
       if (state === undefined) {
         throw new Error('OnDocWithState: state not found')
@@ -46,7 +46,7 @@ export async function OnDocWithState (tx: Tx, txFactory: TxFactory, findAll: Fin
     }
   } else if (tx._class === core.class.TxRemoveDoc) {
     const removeTx = tx as TxRemoveDoc<DocWithState>
-    if (hierarchy.isDerived(removeTx.objectClass, core.class.DocWithState)) {
+    if (hierarchy.isImplements(removeTx.objectClass, core.interface.DocWithState)) {
       const kanban = (await (findAll as FindAll<Kanban>)(view.class.Kanban, { attachedTo: removeTx.objectSpace }))[0]
       if (kanban === undefined) {
         throw new Error('OnDocWithState: kanban not found')