diff --git a/rsconcept/backend/apps/oss/tests/s_propagation/t_constituents.py b/rsconcept/backend/apps/oss/tests/s_propagation/t_constituents.py
index 84732cf0..ae7ed1d5 100644
--- a/rsconcept/backend/apps/oss/tests/s_propagation/t_constituents.py
+++ b/rsconcept/backend/apps/oss/tests/s_propagation/t_constituents.py
@@ -56,6 +56,7 @@ class TestChangeConstituents(EndpointTester):
         self.operation3.refresh_from_db()
         self.ks3 = RSForm(self.operation3.result)
         self.assertEqual(self.ks3.constituentsQ().count(), 4)
+        self.ks3X1 = Constituenta.objects.get(as_child__parent_id=self.ks1X1.pk)
 
         self.layout_data = [
             {'nodeID': 'o' + str(self.operation1.pk), 'x': 0, 'y': 0, 'width': 150, 'height': 40},
@@ -142,6 +143,29 @@ class TestChangeConstituents(EndpointTester):
         self.assertEqual(inherited_cst.definition_raw, r'@{X2|sing,datv}')
 
 
+    @decl_endpoint('/api/rsforms/{item}/update-cst', method='patch')
+    def test_update_constituenta_inherited(self):
+        data = {
+            'target': self.ks3X1.pk,
+            'item_data': {
+                'definition_formal': r'123',
+            }
+        }
+        self.executeBadData(data, item=self.ks3.model.pk)
+
+        data = {
+            'target': self.ks3X1.pk,
+            'item_data': {
+                'term_raw': r'42',
+                'convention': r'1337',
+            }
+        }
+        self.executeOK(data, item=self.ks3.model.pk)
+        self.ks3X1.refresh_from_db()
+        self.assertEqual(self.ks3X1.term_raw, data['item_data']['term_raw'])
+        self.assertEqual(self.ks3X1.convention, data['item_data']['convention'])
+
+
     @decl_endpoint('/api/rsforms/{item}/delete-multiple-cst', method='patch')
     def test_delete_constituenta(self):
         data = {'items': [self.ks2X1.pk]}
diff --git a/rsconcept/backend/apps/rsform/serializers/data_access.py b/rsconcept/backend/apps/rsform/serializers/data_access.py
index 78f534c9..f1d52494 100644
--- a/rsconcept/backend/apps/rsform/serializers/data_access.py
+++ b/rsconcept/backend/apps/rsform/serializers/data_access.py
@@ -116,6 +116,11 @@ class CstUpdateSerializer(StrictSerializer):
                 raise serializers.ValidationError({
                     'alias': msg.aliasTaken(new_alias)
                 })
+        if 'definition_formal' in attrs['item_data']:
+            if Inheritance.objects.filter(child=cst).exists():
+                raise serializers.ValidationError({
+                    'definition_formal': msg.changeInheritedDefinition()
+                })
         return attrs
 
 
diff --git a/rsconcept/backend/apps/rsform/views/rsforms.py b/rsconcept/backend/apps/rsform/views/rsforms.py
index 920c399f..4fe2d638 100644
--- a/rsconcept/backend/apps/rsform/views/rsforms.py
+++ b/rsconcept/backend/apps/rsform/views/rsforms.py
@@ -148,7 +148,7 @@ class RSFormViewSet(viewsets.GenericViewSet, generics.ListAPIView, generics.Retr
         )
 
     @extend_schema(
-        summary='update crucial attributes of a given list of constituents',
+        summary='update crucial attribute of a given list of constituents',
         tags=['RSForm'],
         request=s.CrucialUpdateSerializer,
         responses={
@@ -160,7 +160,7 @@ class RSFormViewSet(viewsets.GenericViewSet, generics.ListAPIView, generics.Retr
     )
     @action(detail=True, methods=['patch'], url_path='update-crucial')
     def update_crucial(self, request: Request, pk) -> HttpResponse:
-        ''' Update crucial attributes of a given list of constituents. '''
+        ''' Update crucial attribute of a given list of constituents. '''
         item = self._get_item()
         serializer = s.CrucialUpdateSerializer(data=request.data, partial=True, context={'schema': item})
         serializer.is_valid(raise_exception=True)
diff --git a/rsconcept/backend/shared/messages.py b/rsconcept/backend/shared/messages.py
index 94236151..91440752 100644
--- a/rsconcept/backend/shared/messages.py
+++ b/rsconcept/backend/shared/messages.py
@@ -22,6 +22,10 @@ def constituentaNotInRSform(title: str):
     return f'Конституента не принадлежит схеме: {title}'
 
 
+def changeInheritedDefinition():
+    return 'Нельзя изменить определение наследника'
+
+
 def constituentaNotFromOperation():
     return 'Конституента не соответствую аргументам операции'
 
diff --git a/rsconcept/frontend/src/components/flow/use-continous-panning.tsx b/rsconcept/frontend/src/components/flow/use-continuous-panning.tsx
similarity index 100%
rename from rsconcept/frontend/src/components/flow/use-continous-panning.tsx
rename to rsconcept/frontend/src/components/flow/use-continuous-panning.tsx
diff --git a/rsconcept/frontend/src/features/rsform/backend/rsform-loader.ts b/rsconcept/frontend/src/features/rsform/backend/rsform-loader.ts
index a14f5c75..0cf2c3df 100644
--- a/rsconcept/frontend/src/features/rsform/backend/rsform-loader.ts
+++ b/rsconcept/frontend/src/features/rsform/backend/rsform-loader.ts
@@ -88,7 +88,7 @@ export class RSFormLoader {
       cst.spawn = [];
       cst.attributes = [];
       cst.spawn_alias = [];
-      cst.parent_schema = schemaByCst.get(cst.id);
+      cst.parent_schema = schemaByCst.get(cst.id) ?? null;
       cst.parent_schema_index = cst.parent_schema ? parents.indexOf(cst.parent_schema) + 1 : 0;
       cst.is_inherited = inherit_children.has(cst.id);
       cst.has_inherited_children = inherit_parents.has(cst.id);
diff --git a/rsconcept/frontend/src/features/rsform/components/term-graph/schemas-guide.tsx b/rsconcept/frontend/src/features/rsform/components/term-graph/schemas-guide.tsx
index 5b92b38b..4b9f1ea2 100644
--- a/rsconcept/frontend/src/features/rsform/components/term-graph/schemas-guide.tsx
+++ b/rsconcept/frontend/src/features/rsform/components/term-graph/schemas-guide.tsx
@@ -19,7 +19,7 @@ export function SchemasGuide({ schema }: SchemasGuideProps) {
     const aliases: string[] = [];
     const indexes: number[] = [];
     schema.items.forEach(cst => {
-      if (cst.parent_schema && !processed.has(cst.parent_schema)) {
+      if (cst.parent_schema !== null && !processed.has(cst.parent_schema)) {
         const item = libraryItems.find(item => item.id === cst.parent_schema);
         if (item) {
           aliases.push(item.alias);
diff --git a/rsconcept/frontend/src/features/rsform/models/rsform.ts b/rsconcept/frontend/src/features/rsform/models/rsform.ts
index a12907fc..16e4ac37 100644
--- a/rsconcept/frontend/src/features/rsform/models/rsform.ts
+++ b/rsconcept/frontend/src/features/rsform/models/rsform.ts
@@ -86,7 +86,7 @@ export interface IConstituenta {
    */
   parent_schema_index: number;
   /** {@link LibraryItem} that contains parent of this inherited {@link IConstituenta}. */
-  parent_schema?: number;
+  parent_schema: number | null;
   /** Indicates if this {@link IConstituenta} is inherited. */
   is_inherited: boolean;
   /** Indicates if this {@link IConstituenta} has children that are inherited. */
diff --git a/rsconcept/frontend/src/features/rsform/pages/rsform-page/editor-term-graph/tg-flow.tsx b/rsconcept/frontend/src/features/rsform/pages/rsform-page/editor-term-graph/tg-flow.tsx
index e040b743..ecbfcae9 100644
--- a/rsconcept/frontend/src/features/rsform/pages/rsform-page/editor-term-graph/tg-flow.tsx
+++ b/rsconcept/frontend/src/features/rsform/pages/rsform-page/editor-term-graph/tg-flow.tsx
@@ -15,7 +15,7 @@ import {
 import clsx from 'clsx';
 
 import { DiagramFlow, useReactFlow } from '@/components/flow/diagram-flow';
-import { useContinuousPan } from '@/components/flow/use-continous-panning';
+import { useContinuousPan } from '@/components/flow/use-continuous-panning';
 import { useWindowSize } from '@/hooks/use-window-size';
 import { useFitHeight, useMainHeight } from '@/stores/app-layout';
 import { PARAMETER } from '@/utils/constants';
@@ -255,20 +255,26 @@ export function TGFlow() {
 
     const sourceID = Number(connection.source);
     const targetID = Number(connection.target);
-    if (
-      (connectionType === TGEdgeType.attribution && schema.attribution_graph.hasEdge(sourceID, targetID)) ||
-      (connectionType === TGEdgeType.definition && schema.graph.hasEdge(sourceID, targetID))
-    ) {
-      toast.info(errorMsg.connectionExists);
-      return;
+    const sourceCst = schema.cstByID.get(sourceID);
+    const targetCst = schema.cstByID.get(targetID);
+    if (!targetCst || !sourceCst) {
+      throw new Error('Constituents not found');
     }
 
     if (connectionType === TGEdgeType.definition) {
-      const sourceCst = schema.cstByID.get(sourceID);
-      const targetCst = schema.cstByID.get(targetID);
-      if (!targetCst || !sourceCst) {
-        throw new Error('Constituents not found');
+      if (targetCst.is_inherited) {
+        toast.error(errorMsg.changeInheritedDefinition);
+        return;
       }
+      if (schema.graph.hasEdge(sourceID, targetID)) {
+        toast.error(errorMsg.connectionExists);
+        return;
+      }
+      if (schema.graph.isReachable(targetID, sourceID)) {
+        toast.error(errorMsg.cyclingEdge);
+        return;
+      }
+
       const newExpressions = addAliasReference(targetCst.definition_formal, sourceCst.alias);
       void updateConstituenta({
         itemID: schema.id,
@@ -279,8 +285,20 @@ export function TGFlow() {
           }
         }
       });
-      return;
     } else {
+      if (schema.attribution_graph.hasEdge(sourceID, targetID)) {
+        toast.error(errorMsg.connectionExists);
+        return;
+      }
+      if (schema.attribution_graph.isReachable(targetID, sourceID)) {
+        toast.error(errorMsg.cyclingEdge);
+        return;
+      }
+      if (targetCst.parent_schema !== null && targetCst.parent_schema === sourceCst.parent_schema) {
+        toast.error(errorMsg.addInheritedEdge);
+        return;
+      }
+
       void createAttribution({
         itemID: schema.id,
         data: {
diff --git a/rsconcept/frontend/src/features/rsform/pages/rsform-page/rsedit-state.tsx b/rsconcept/frontend/src/features/rsform/pages/rsform-page/rsedit-state.tsx
index bfb1ea95..fdfc2d1f 100644
--- a/rsconcept/frontend/src/features/rsform/pages/rsform-page/rsedit-state.tsx
+++ b/rsconcept/frontend/src/features/rsform/pages/rsform-page/rsedit-state.tsx
@@ -1,6 +1,7 @@
 'use client';
 
 import { useEffect, useState } from 'react';
+import { toast } from 'react-toastify';
 
 import { urls, useConceptNavigation } from '@/app';
 import { useAIStore } from '@/features/ai/stores/ai-context';
@@ -14,7 +15,7 @@ import { useDialogsStore } from '@/stores/dialogs';
 import { useModificationStore } from '@/stores/modification';
 import { usePreferencesStore } from '@/stores/preferences';
 import { PARAMETER, prefixes } from '@/utils/constants';
-import { promptText } from '@/utils/labels';
+import { errorMsg, promptText } from '@/utils/labels';
 import { type RO } from '@/utils/meta';
 import { promptUnsaved } from '@/utils/utils';
 
@@ -302,7 +303,16 @@ export const RSEditState = ({
     const ids = selectedEdges[0].split('-');
     const sourceID = Number(ids[0]);
     const targetID = Number(ids[1]);
+    const sourceCst = schema.cstByID.get(sourceID);
+    const targetCst = schema.cstByID.get(targetID);
+    if (!targetCst || !sourceCst) {
+      throw new Error('Constituents not found');
+    }
     if (schema.attribution_graph.hasEdge(sourceID, targetID)) {
+      if (targetCst.parent_schema !== null && targetCst.parent_schema === sourceCst.parent_schema) {
+        toast.error(errorMsg.deleteInheritedEdge);
+        return;
+      }
       void deleteAttribution({
         itemID: schema.id,
         data: {
@@ -311,10 +321,9 @@ export const RSEditState = ({
         }
       });
     } else if (schema.graph.hasEdge(sourceID, targetID)) {
-      const sourceCst = schema.cstByID.get(sourceID);
-      const targetCst = schema.cstByID.get(targetID);
-      if (!targetCst || !sourceCst) {
-        throw new Error('Constituents not found');
+      if (targetCst.is_inherited) {
+        toast.error(errorMsg.changeInheritedDefinition);
+        return;
       }
       const newExpressions = removeAliasReference(targetCst.definition_formal, sourceCst.alias);
       void updateConstituenta({
diff --git a/rsconcept/frontend/src/models/graph.ts b/rsconcept/frontend/src/models/graph.ts
index c53c4058..bea552e4 100644
--- a/rsconcept/frontend/src/models/graph.ts
+++ b/rsconcept/frontend/src/models/graph.ts
@@ -149,6 +149,10 @@ export class Graph<NodeID = number> {
     return !!sourceNode.outputs.find(id => id === destination);
   }
 
+  isReachable(source: NodeID, destination: NodeID): boolean {
+    return this.expandAllOutputs([source]).includes(destination);
+  }
+
   rootNodes(): NodeID[] {
     return [...this.nodes.keys()].filter(id => !this.nodes.get(id)?.inputs.length);
   }
diff --git a/rsconcept/frontend/src/utils/labels.ts b/rsconcept/frontend/src/utils/labels.ts
index 2b89e347..631c7a37 100644
--- a/rsconcept/frontend/src/utils/labels.ts
+++ b/rsconcept/frontend/src/utils/labels.ts
@@ -70,7 +70,11 @@ export const errorMsg = {
   invalidLocation: 'Некорректный формат пути',
   emptySubstitutions: 'Выберите хотя бы одно отождествление',
   invalidResponse: 'Некорректный ответ сервера',
-  connectionExists: 'Связь уже существует'
+  connectionExists: 'Связь уже существует',
+  cyclingEdge: 'Связь образует цикл',
+  changeInheritedDefinition: 'Нельзя изменить определение наследника',
+  addInheritedEdge: 'Новая связь между наследниками из одной схемы не допускается',
+  deleteInheritedEdge: 'Нельзя удалить связь между наследниками из одной схемы'
 } as const;
 
 /**