diff --git a/rsconcept/frontend/src/backend/cctext/api.ts b/rsconcept/frontend/src/backend/cctext/api.ts
index 210ca1bc..c89e2311 100644
--- a/rsconcept/frontend/src/backend/cctext/api.ts
+++ b/rsconcept/frontend/src/backend/cctext/api.ts
@@ -1,5 +1,4 @@
 import { axiosPost } from '@/backend/apiTransport';
-import { ILexemeData, IWordFormPlain } from '@/models/language';
 
 /**
  * Represents API result for text output.
@@ -8,11 +7,26 @@ export interface ITextResult {
   result: string;
 }
 
+/**
+ * Represents wordform data used for backend communication.
+ */
+export interface IWordFormDTO {
+  text: string;
+  grams: string;
+}
+
+/**
+ * Represents lexeme response containing multiple {@link Wordform}s.
+ */
+export interface ILexemeResponse {
+  items: IWordFormDTO[];
+}
+
 export const cctextApi = {
   baseKey: 'cctext',
 
-  inflectText: (data: IWordFormPlain) =>
-    axiosPost<IWordFormPlain, ITextResult>({
+  inflectText: (data: IWordFormDTO) =>
+    axiosPost<IWordFormDTO, ITextResult>({
       endpoint: '/api/cctext/inflect',
       request: { data: data }
     }),
@@ -22,7 +36,7 @@ export const cctextApi = {
       request: { data: data }
     }),
   generateLexeme: (data: { text: string }) =>
-    axiosPost<{ text: string }, ILexemeData>({
+    axiosPost<{ text: string }, ILexemeResponse>({
       endpoint: '/api/cctext/generate-lexeme',
       request: { data: data }
     })
diff --git a/rsconcept/frontend/src/backend/cctext/useGenerateLexeme.tsx b/rsconcept/frontend/src/backend/cctext/useGenerateLexeme.tsx
index c96479ca..f0f79014 100644
--- a/rsconcept/frontend/src/backend/cctext/useGenerateLexeme.tsx
+++ b/rsconcept/frontend/src/backend/cctext/useGenerateLexeme.tsx
@@ -1,9 +1,8 @@
 import { useMutation } from '@tanstack/react-query';
 
 import { DataCallback } from '@/backend/apiTransport';
-import { ILexemeData } from '@/models/language';
 
-import { cctextApi } from './api';
+import { cctextApi, ILexemeResponse } from './api';
 
 export const useGenerateLexeme = () => {
   const mutation = useMutation({
@@ -13,7 +12,7 @@ export const useGenerateLexeme = () => {
   return {
     generateLexeme: (
       data: { text: string }, //
-      onSuccess?: DataCallback<ILexemeData>
+      onSuccess?: DataCallback<ILexemeResponse>
     ) => mutation.mutate(data, { onSuccess })
   };
 };
diff --git a/rsconcept/frontend/src/backend/cctext/useInflectText.tsx b/rsconcept/frontend/src/backend/cctext/useInflectText.tsx
index a8239263..24da915d 100644
--- a/rsconcept/frontend/src/backend/cctext/useInflectText.tsx
+++ b/rsconcept/frontend/src/backend/cctext/useInflectText.tsx
@@ -1,9 +1,8 @@
 import { useMutation } from '@tanstack/react-query';
 
 import { DataCallback } from '@/backend/apiTransport';
-import { IWordFormPlain } from '@/models/language';
 
-import { cctextApi, ITextResult } from './api';
+import { cctextApi, ITextResult, IWordFormDTO } from './api';
 
 export const useInflectText = () => {
   const mutation = useMutation({
@@ -12,7 +11,7 @@ export const useInflectText = () => {
   });
   return {
     inflectText: (
-      data: IWordFormPlain, //
+      data: IWordFormDTO, //
       onSuccess?: DataCallback<ITextResult>
     ) => mutation.mutate(data, { onSuccess })
   };
diff --git a/rsconcept/frontend/src/backend/library/api.ts b/rsconcept/frontend/src/backend/library/api.ts
index be076512..73212e3c 100644
--- a/rsconcept/frontend/src/backend/library/api.ts
+++ b/rsconcept/frontend/src/backend/library/api.ts
@@ -3,7 +3,7 @@ import { queryOptions } from '@tanstack/react-query';
 import { axiosDelete, axiosGet, axiosPatch, axiosPost } from '@/backend/apiTransport';
 import { DELAYS } from '@/backend/configuration';
 import { ossApi } from '@/backend/oss/api';
-import { rsformsApi } from '@/backend/rsform/api';
+import { IRSFormDTO, rsformsApi } from '@/backend/rsform/api';
 import {
   AccessPolicy,
   ILibraryItem,
@@ -13,7 +13,7 @@ import {
   LibraryItemType,
   VersionID
 } from '@/models/library';
-import { ConstituentaID, IRSFormData } from '@/models/rsform';
+import { ConstituentaID } from '@/models/rsform';
 import { UserID } from '@/models/user';
 import { information } from '@/utils/labels';
 
@@ -60,7 +60,7 @@ export interface IVersionCreateDTO {
  */
 export interface IVersionCreatedResponse {
   version: number;
-  schema: IRSFormData;
+  schema: IRSFormDTO;
 }
 
 export const libraryApi = {
@@ -157,7 +157,7 @@ export const libraryApi = {
       }
     }),
   cloneItem: (data: IRSFormCloneDTO) =>
-    axiosPost<IRSFormCloneDTO, IRSFormData>({
+    axiosPost<IRSFormCloneDTO, IRSFormDTO>({
       endpoint: `/api/library/${data.id}/clone`,
       request: {
         data: data,
@@ -182,7 +182,7 @@ export const libraryApi = {
       }
     }),
   versionRestore: ({ versionID }: { versionID: VersionID }) =>
-    axiosPatch<undefined, IRSFormData>({
+    axiosPatch<undefined, IRSFormDTO>({
       endpoint: `/api/versions/${versionID}/restore`,
       request: {
         successMessage: information.versionRestored
diff --git a/rsconcept/frontend/src/backend/library/useCloneItem.tsx b/rsconcept/frontend/src/backend/library/useCloneItem.tsx
index 219aad9d..dc9b0910 100644
--- a/rsconcept/frontend/src/backend/library/useCloneItem.tsx
+++ b/rsconcept/frontend/src/backend/library/useCloneItem.tsx
@@ -1,8 +1,8 @@
 import { useMutation, useQueryClient } from '@tanstack/react-query';
 
 import { DataCallback } from '@/backend/apiTransport';
-import { IRSFormData } from '@/models/rsform';
 
+import { IRSFormDTO } from '../rsform/api';
 import { IRSFormCloneDTO, libraryApi } from './api';
 
 export const useCloneItem = () => {
@@ -15,7 +15,7 @@ export const useCloneItem = () => {
   return {
     cloneItem: (
       data: IRSFormCloneDTO, //
-      onSuccess?: DataCallback<IRSFormData>
+      onSuccess?: DataCallback<IRSFormDTO>
     ) => mutation.mutate(data, { onSuccess })
   };
 };
diff --git a/rsconcept/frontend/src/backend/library/useSetAccessPolicy.tsx b/rsconcept/frontend/src/backend/library/useSetAccessPolicy.tsx
index 1754b768..37f27303 100644
--- a/rsconcept/frontend/src/backend/library/useSetAccessPolicy.tsx
+++ b/rsconcept/frontend/src/backend/library/useSetAccessPolicy.tsx
@@ -1,9 +1,8 @@
 import { useMutation, useQueryClient } from '@tanstack/react-query';
 
-import { ossApi } from '@/backend/oss/api';
+import { IOperationSchemaDTO, ossApi } from '@/backend/oss/api';
 import { rsformsApi } from '@/backend/rsform/api';
 import { AccessPolicy, ILibraryItem, LibraryItemID } from '@/models/library';
-import { IOperationSchemaData } from '@/models/oss';
 
 import { libraryApi } from './api';
 
@@ -14,7 +13,7 @@ export const useSetAccessPolicy = () => {
     mutationFn: libraryApi.setAccessPolicy,
     onSuccess: (_, variables) => {
       const ossKey = ossApi.getOssQueryOptions({ itemID: variables.itemID }).queryKey;
-      const ossData: IOperationSchemaData | undefined = client.getQueryData(ossKey);
+      const ossData: IOperationSchemaDTO | undefined = client.getQueryData(ossKey);
       if (ossData) {
         client.setQueryData(ossKey, { ...ossData, access_policy: variables.policy });
         return Promise.allSettled([
diff --git a/rsconcept/frontend/src/backend/library/useSetLocation.tsx b/rsconcept/frontend/src/backend/library/useSetLocation.tsx
index 80803e83..2dcaa19e 100644
--- a/rsconcept/frontend/src/backend/library/useSetLocation.tsx
+++ b/rsconcept/frontend/src/backend/library/useSetLocation.tsx
@@ -1,9 +1,8 @@
 import { useMutation, useQueryClient } from '@tanstack/react-query';
 
-import { ossApi } from '@/backend/oss/api';
+import { IOperationSchemaDTO, ossApi } from '@/backend/oss/api';
 import { rsformsApi } from '@/backend/rsform/api';
 import { ILibraryItem, LibraryItemID } from '@/models/library';
-import { IOperationSchemaData } from '@/models/oss';
 
 import { libraryApi } from './api';
 
@@ -14,7 +13,7 @@ export const useSetLocation = () => {
     mutationFn: libraryApi.setLocation,
     onSuccess: (_, variables) => {
       const ossKey = ossApi.getOssQueryOptions({ itemID: variables.itemID }).queryKey;
-      const ossData: IOperationSchemaData | undefined = client.getQueryData(ossKey);
+      const ossData: IOperationSchemaDTO | undefined = client.getQueryData(ossKey);
       if (ossData) {
         client.setQueryData(ossKey, { ...ossData, location: variables.location });
         return Promise.allSettled([
diff --git a/rsconcept/frontend/src/backend/library/useSetOwner.tsx b/rsconcept/frontend/src/backend/library/useSetOwner.tsx
index 7ec5ff84..09bd4ef9 100644
--- a/rsconcept/frontend/src/backend/library/useSetOwner.tsx
+++ b/rsconcept/frontend/src/backend/library/useSetOwner.tsx
@@ -1,9 +1,8 @@
 import { useMutation, useQueryClient } from '@tanstack/react-query';
 
-import { ossApi } from '@/backend/oss/api';
+import { IOperationSchemaDTO, ossApi } from '@/backend/oss/api';
 import { rsformsApi } from '@/backend/rsform/api';
 import { ILibraryItem, LibraryItemID } from '@/models/library';
-import { IOperationSchemaData } from '@/models/oss';
 import { UserID } from '@/models/user';
 
 import { libraryApi } from './api';
@@ -15,7 +14,7 @@ export const useSetOwner = () => {
     mutationFn: libraryApi.setOwner,
     onSuccess: (_, variables) => {
       const ossKey = ossApi.getOssQueryOptions({ itemID: variables.itemID }).queryKey;
-      const ossData: IOperationSchemaData | undefined = client.getQueryData(ossKey);
+      const ossData: IOperationSchemaDTO | undefined = client.getQueryData(ossKey);
       if (ossData) {
         client.setQueryData(ossKey, { ...ossData, owner: variables.owner });
         return Promise.allSettled([
diff --git a/rsconcept/frontend/src/backend/library/useUpdateItem.tsx b/rsconcept/frontend/src/backend/library/useUpdateItem.tsx
index 4c53e9ed..4f2f689b 100644
--- a/rsconcept/frontend/src/backend/library/useUpdateItem.tsx
+++ b/rsconcept/frontend/src/backend/library/useUpdateItem.tsx
@@ -1,10 +1,9 @@
 import { useMutation, useQueryClient } from '@tanstack/react-query';
 
-import { ossApi } from '@/backend/oss/api';
+import { IOperationSchemaDTO, ossApi } from '@/backend/oss/api';
 import { ILibraryItem, LibraryItemType } from '@/models/library';
-import { IOperationSchemaData } from '@/models/oss';
-import { IRSFormData } from '@/models/rsform';
 
+import { IRSFormDTO } from '../rsform/api';
 import { ILibraryUpdateDTO, libraryApi } from './api';
 
 export const useUpdateItem = () => {
@@ -17,11 +16,11 @@ export const useUpdateItem = () => {
       client.setQueryData(libraryApi.libraryListKey, (prev: ILibraryItem[] | undefined) =>
         prev?.map(item => (item.id === data.id ? data : item))
       );
-      client.setQueryData(itemKey, (prev: IRSFormData | IOperationSchemaData | undefined) =>
+      client.setQueryData(itemKey, (prev: IRSFormDTO | IOperationSchemaDTO | undefined) =>
         !prev ? undefined : { ...prev, ...data }
       );
       if (data.item_type === LibraryItemType.RSFORM) {
-        const schema: IRSFormData | undefined = client.getQueryData(itemKey);
+        const schema: IRSFormDTO | undefined = client.getQueryData(itemKey);
         if (schema) {
           return Promise.allSettled(
             schema.oss.map(item =>
diff --git a/rsconcept/frontend/src/backend/library/useVersionDelete.tsx b/rsconcept/frontend/src/backend/library/useVersionDelete.tsx
index ec3765a8..df6fa608 100644
--- a/rsconcept/frontend/src/backend/library/useVersionDelete.tsx
+++ b/rsconcept/frontend/src/backend/library/useVersionDelete.tsx
@@ -1,8 +1,7 @@
 import { useMutation, useQueryClient } from '@tanstack/react-query';
 
-import { rsformsApi } from '@/backend/rsform/api';
+import { IRSFormDTO, rsformsApi } from '@/backend/rsform/api';
 import { LibraryItemID, VersionID } from '@/models/library';
-import { IRSFormData } from '@/models/rsform';
 
 import { libraryApi } from './api';
 
@@ -14,7 +13,7 @@ export const useVersionDelete = () => {
     onSuccess: (_, variables) => {
       client.setQueryData(
         rsformsApi.getRSFormQueryOptions({ itemID: variables.itemID }).queryKey,
-        (prev: IRSFormData | undefined) =>
+        (prev: IRSFormDTO | undefined) =>
           !prev
             ? undefined
             : {
diff --git a/rsconcept/frontend/src/backend/library/useVersionUpdate.tsx b/rsconcept/frontend/src/backend/library/useVersionUpdate.tsx
index 7507f023..2967598c 100644
--- a/rsconcept/frontend/src/backend/library/useVersionUpdate.tsx
+++ b/rsconcept/frontend/src/backend/library/useVersionUpdate.tsx
@@ -1,8 +1,7 @@
 import { useMutation, useQueryClient } from '@tanstack/react-query';
 
-import { rsformsApi } from '@/backend/rsform/api';
+import { IRSFormDTO, rsformsApi } from '@/backend/rsform/api';
 import { IVersionData, VersionID } from '@/models/library';
-import { IRSFormData } from '@/models/rsform';
 
 import { libraryApi } from './api';
 
@@ -14,7 +13,7 @@ export const useVersionUpdate = () => {
     onSuccess: data => {
       client.setQueryData(
         rsformsApi.getRSFormQueryOptions({ itemID: data.item }).queryKey,
-        (prev: IRSFormData | undefined) =>
+        (prev: IRSFormDTO | undefined) =>
           !prev
             ? undefined
             : {
diff --git a/rsconcept/frontend/src/models/OssLoader.ts b/rsconcept/frontend/src/backend/oss/OssLoader.ts
similarity index 87%
rename from rsconcept/frontend/src/models/OssLoader.ts
rename to rsconcept/frontend/src/backend/oss/OssLoader.ts
index ed16daf2..36a673fc 100644
--- a/rsconcept/frontend/src/models/OssLoader.ts
+++ b/rsconcept/frontend/src/backend/oss/OssLoader.ts
@@ -2,29 +2,24 @@
  * Module: OSS data loading and processing.
  */
 
-import { Graph } from './Graph';
-import { ILibraryItem, LibraryItemID } from './library';
-import {
-  IOperation,
-  IOperationSchema,
-  IOperationSchemaData,
-  IOperationSchemaStats,
-  OperationID,
-  OperationType
-} from './oss';
+import { Graph } from '@/models/Graph';
+import { ILibraryItem, LibraryItemID } from '@/models/library';
+import { IOperation, IOperationSchema, IOperationSchemaStats, OperationID, OperationType } from '@/models/oss';
+
+import { IOperationSchemaDTO } from './api';
 
 /**
- * Loads data into an {@link IOperationSchema} based on {@link IOperationSchemaData}.
+ * Loads data into an {@link IOperationSchema} based on {@link IOperationSchemaDTO}.
  *
  */
 export class OssLoader {
-  private oss: IOperationSchemaData;
+  private oss: IOperationSchemaDTO;
   private graph: Graph = new Graph();
   private operationByID = new Map<OperationID, IOperation>();
   private schemaIDs: LibraryItemID[] = [];
   private items: ILibraryItem[];
 
-  constructor(input: IOperationSchemaData, items: ILibraryItem[]) {
+  constructor(input: IOperationSchemaDTO, items: ILibraryItem[]) {
     this.oss = input;
     this.items = items;
   }
diff --git a/rsconcept/frontend/src/backend/oss/api.ts b/rsconcept/frontend/src/backend/oss/api.ts
index aed0bcaa..04516828 100644
--- a/rsconcept/frontend/src/backend/oss/api.ts
+++ b/rsconcept/frontend/src/backend/oss/api.ts
@@ -2,18 +2,33 @@ import { queryOptions } from '@tanstack/react-query';
 
 import { axiosDelete, axiosGet, axiosPatch, axiosPost } from '@/backend/apiTransport';
 import { DELAYS } from '@/backend/configuration';
-import { ILibraryItem, LibraryItemID } from '@/models/library';
+import { ILibraryItem, ILibraryItemData, LibraryItemID } from '@/models/library';
 import {
+  IArgument,
   ICstSubstitute,
-  IOperationData,
+  ICstSubstituteEx,
+  IOperation,
   IOperationPosition,
-  IOperationSchemaData,
   OperationID,
   OperationType
 } from '@/models/oss';
 import { ConstituentaID, IConstituentaReference, ITargetCst } from '@/models/rsform';
 import { information } from '@/utils/labels';
 
+/**
+ * Represents {@link IOperation} data from server.
+ */
+export interface IOperationDTO extends Omit<IOperation, 'substitutions' | 'arguments'> {}
+
+/**
+ * Represents backend data for {@link IOperationSchema}.
+ */
+export interface IOperationSchemaDTO extends ILibraryItemData {
+  items: IOperationDTO[];
+  arguments: IArgument[];
+  substitutions: ICstSubstituteEx[];
+}
+
 /**
  * Represents {@link IOperation} data, used in creation process.
  */
@@ -36,8 +51,8 @@ export interface IOperationCreateDTO {
  * Represents data response when creating {@link IOperation}.
  */
 export interface IOperationCreatedResponse {
-  new_operation: IOperationData;
-  oss: IOperationSchemaData;
+  new_operation: IOperationDTO;
+  oss: IOperationSchemaDTO;
 }
 
 /**
@@ -61,7 +76,7 @@ export interface IOperationDeleteDTO extends ITargetOperation {
  */
 export interface IInputCreatedResponse {
   new_schema: ILibraryItem;
-  oss: IOperationSchemaData;
+  oss: IOperationSchemaDTO;
 }
 
 /**
@@ -102,7 +117,7 @@ export const ossApi = {
       queryFn: meta =>
         !itemID
           ? undefined
-          : axiosGet<IOperationSchemaData>({
+          : axiosGet<IOperationSchemaDTO>({
               endpoint: `/api/oss/${itemID}/details`,
               options: { signal: meta.signal }
             })
@@ -135,7 +150,7 @@ export const ossApi = {
       }
     }),
   operationDelete: ({ itemID, data }: { itemID: LibraryItemID; data: IOperationDeleteDTO }) =>
-    axiosDelete<IOperationDeleteDTO, IOperationSchemaData>({
+    axiosDelete<IOperationDeleteDTO, IOperationSchemaDTO>({
       endpoint: `/api/oss/${itemID}/delete-operation`,
       request: {
         data: data,
@@ -151,7 +166,7 @@ export const ossApi = {
       }
     }),
   inputUpdate: ({ itemID, data }: { itemID: LibraryItemID; data: IInputUpdateDTO }) =>
-    axiosPatch<IInputUpdateDTO, IOperationSchemaData>({
+    axiosPatch<IInputUpdateDTO, IOperationSchemaDTO>({
       endpoint: `/api/oss/${itemID}/set-input`,
       request: {
         data: data,
@@ -159,7 +174,7 @@ export const ossApi = {
       }
     }),
   operationUpdate: ({ itemID, data }: { itemID: LibraryItemID; data: IOperationUpdateDTO }) =>
-    axiosPatch<IOperationUpdateDTO, IOperationSchemaData>({
+    axiosPatch<IOperationUpdateDTO, IOperationSchemaDTO>({
       endpoint: `/api/oss/${itemID}/update-operation`,
       request: {
         data: data,
@@ -167,7 +182,7 @@ export const ossApi = {
       }
     }),
   operationExecute: ({ itemID, data }: { itemID: LibraryItemID; data: ITargetOperation }) =>
-    axiosPost<ITargetOperation, IOperationSchemaData>({
+    axiosPost<ITargetOperation, IOperationSchemaDTO>({
       endpoint: `/api/oss/${itemID}/execute-operation`,
       request: {
         data: data,
@@ -176,7 +191,7 @@ export const ossApi = {
     }),
 
   relocateConstituents: ({ itemID, data }: { itemID: LibraryItemID; data: ICstRelocateDTO }) =>
-    axiosPost<ICstRelocateDTO, IOperationSchemaData>({
+    axiosPost<ICstRelocateDTO, IOperationSchemaDTO>({
       endpoint: `/api/oss/${itemID}/relocate-constituents`,
       request: {
         data: data,
diff --git a/rsconcept/frontend/src/backend/oss/useOSS.tsx b/rsconcept/frontend/src/backend/oss/useOSS.tsx
index 70c88211..7805b707 100644
--- a/rsconcept/frontend/src/backend/oss/useOSS.tsx
+++ b/rsconcept/frontend/src/backend/oss/useOSS.tsx
@@ -1,8 +1,8 @@
 import { useQuery, useSuspenseQuery } from '@tanstack/react-query';
 
 import { useLibrary, useLibrarySuspense } from '@/backend/library/useLibrary';
+import { OssLoader } from '@/backend/oss/OssLoader';
 import { LibraryItemID } from '@/models/library';
-import { OssLoader } from '@/models/OssLoader';
 
 import { queryClient } from '../queryClient';
 import { ossApi } from './api';
diff --git a/rsconcept/frontend/src/backend/oss/useOperationCreate.tsx b/rsconcept/frontend/src/backend/oss/useOperationCreate.tsx
index e1187712..97ca7167 100644
--- a/rsconcept/frontend/src/backend/oss/useOperationCreate.tsx
+++ b/rsconcept/frontend/src/backend/oss/useOperationCreate.tsx
@@ -3,9 +3,8 @@ import { useMutation, useQueryClient } from '@tanstack/react-query';
 import { DataCallback } from '@/backend/apiTransport';
 import { useUpdateTimestamp } from '@/backend/library/useUpdateTimestamp';
 import { LibraryItemID } from '@/models/library';
-import { IOperationData } from '@/models/oss';
 
-import { IOperationCreateDTO, ossApi } from './api';
+import { IOperationCreateDTO, IOperationDTO, ossApi } from './api';
 
 export const useOperationCreate = () => {
   const client = useQueryClient();
@@ -24,7 +23,7 @@ export const useOperationCreate = () => {
         itemID: LibraryItemID; //
         data: IOperationCreateDTO;
       },
-      onSuccess?: DataCallback<IOperationData>
+      onSuccess?: DataCallback<IOperationDTO>
     ) => mutation.mutate(data, { onSuccess: response => onSuccess?.(response.new_operation) })
   };
 };
diff --git a/rsconcept/frontend/src/models/RSFormLoader.ts b/rsconcept/frontend/src/backend/rsform/RSFormLoader.ts
similarity index 93%
rename from rsconcept/frontend/src/models/RSFormLoader.ts
rename to rsconcept/frontend/src/backend/rsform/RSFormLoader.ts
index 9b6dd30b..4d97405b 100644
--- a/rsconcept/frontend/src/models/RSFormLoader.ts
+++ b/rsconcept/frontend/src/backend/rsform/RSFormLoader.ts
@@ -2,27 +2,29 @@
  * Module: RSForm data loading and processing.
  */
 
-import { Graph } from './Graph';
-import { LibraryItemID } from './library';
-import { ConstituentaID, CstType, IConstituenta, IRSForm, IRSFormData, IRSFormStats } from './rsform';
-import { inferClass, inferStatus, inferTemplate, isBaseSet, isFunctional } from './rsformAPI';
-import { ParsingStatus, ValueClass } from './rslang';
-import { extractGlobals, isSimpleExpression, splitTemplateDefinition } from './rslangAPI';
+import { Graph } from '@/models/Graph';
+import { LibraryItemID } from '@/models/library';
+import { ConstituentaID, CstType, IConstituenta, IRSForm, IRSFormStats } from '@/models/rsform';
+import { inferClass, inferStatus, inferTemplate, isBaseSet, isFunctional } from '@/models/rsformAPI';
+import { ParsingStatus, ValueClass } from '@/models/rslang';
+import { extractGlobals, isSimpleExpression, splitTemplateDefinition } from '@/models/rslangAPI';
+
+import { IRSFormDTO } from './api';
 
 /**
- * Loads data into an {@link IRSForm} based on {@link IRSFormData}.
+ * Loads data into an {@link IRSForm} based on {@link IRSFormDTO}.
  *
  * @remarks
  * This function processes the provided input, initializes the IRSForm, and calculates statistics
  * based on the loaded data. It also establishes dependencies between concepts in the graph.
  */
 export class RSFormLoader {
-  private schema: IRSFormData;
+  private schema: IRSFormDTO;
   private graph: Graph = new Graph();
   private cstByAlias = new Map<string, IConstituenta>();
   private cstByID = new Map<ConstituentaID, IConstituenta>();
 
-  constructor(input: IRSFormData) {
+  constructor(input: IRSFormDTO) {
     this.schema = input;
   }
 
@@ -159,7 +161,8 @@ export class RSFormLoader {
       } else if (sources.size !== 1) {
         return false;
       } else {
-        const base = this.cstByID.get(sources.values().next().value!)!;
+        const cstID = sources.values().next().value!;
+        const base = this.cstByID.get(cstID)!;
         return !isFunctional(base.cst_type) || splitTemplateDefinition(base.definition_formal).head !== expression.head;
       }
     };
diff --git a/rsconcept/frontend/src/backend/rsform/api.ts b/rsconcept/frontend/src/backend/rsform/api.ts
index 5b4d9d89..f21986ad 100644
--- a/rsconcept/frontend/src/backend/rsform/api.ts
+++ b/rsconcept/frontend/src/backend/rsform/api.ts
@@ -2,20 +2,42 @@ import { queryOptions } from '@tanstack/react-query';
 
 import { axiosDelete, axiosGet, axiosPatch, axiosPost } from '@/backend/apiTransport';
 import { DELAYS } from '@/backend/configuration';
-import { LibraryItemID, VersionID } from '@/models/library';
+import { ILibraryItemReference, ILibraryItemVersioned, LibraryItemID, VersionID } from '@/models/library';
 import { ICstSubstitute, ICstSubstitutions } from '@/models/oss';
 import {
   ConstituentaID,
   CstType,
   IConstituentaList,
   IConstituentaMeta,
-  IRSFormData,
+  IInheritanceInfo,
   ITargetCst,
   TermForm
 } from '@/models/rsform';
-import { IExpressionParse } from '@/models/rslang';
+import { IArgumentInfo, IExpressionParse, ParsingStatus, ValueClass } from '@/models/rslang';
 import { information } from '@/utils/labels';
 
+/**
+ * Represents {@link IConstituenta} data from server.
+ */
+export interface IConstituentaDTO extends IConstituentaMeta {
+  parse: {
+    status: ParsingStatus;
+    valueClass: ValueClass;
+    typification: string;
+    syntaxTree: string;
+    args: IArgumentInfo[];
+  };
+}
+
+/**
+ * Represents data for {@link IRSForm} provided by backend.
+ */
+export interface IRSFormDTO extends ILibraryItemVersioned {
+  items: IConstituentaDTO[];
+  inheritance: IInheritanceInfo[];
+  oss: ILibraryItemReference[];
+}
+
 /**
  * Represents data, used for uploading {@link IRSForm} as file.
  */
@@ -46,7 +68,7 @@ export interface ICstCreateDTO {
  */
 export interface ICstCreatedResponse {
   new_cst: IConstituentaMeta;
-  schema: IRSFormData;
+  schema: IRSFormDTO;
 }
 
 /**
@@ -85,7 +107,7 @@ export interface ICstMoveDTO {
  */
 export interface IProduceStructureResponse {
   cst_list: ConstituentaID[];
-  schema: IRSFormData;
+  schema: IRSFormDTO;
 }
 
 /**
@@ -117,7 +139,7 @@ export const rsformsApi = {
       queryFn: meta =>
         !itemID
           ? undefined
-          : axiosGet<IRSFormData>({
+          : axiosGet<IRSFormDTO>({
               endpoint: version ? `/api/library/${itemID}/versions/${version}` : `/api/rsforms/${itemID}/details`,
               options: { signal: meta.signal }
             })
@@ -130,7 +152,7 @@ export const rsformsApi = {
       options: { responseType: 'blob' }
     }),
   upload: (data: IRSFormUploadDTO) =>
-    axiosPatch<IRSFormUploadDTO, IRSFormData>({
+    axiosPatch<IRSFormUploadDTO, IRSFormDTO>({
       endpoint: `/api/rsforms/${data.itemID}/load-trs`,
       request: {
         data: data,
@@ -160,7 +182,7 @@ export const rsformsApi = {
       }
     }),
   cstDelete: ({ itemID, data }: { itemID: LibraryItemID; data: IConstituentaList }) =>
-    axiosDelete<IConstituentaList, IRSFormData>({
+    axiosDelete<IConstituentaList, IRSFormDTO>({
       endpoint: `/api/rsforms/${itemID}/delete-multiple-cst`,
       request: {
         data: data,
@@ -176,7 +198,7 @@ export const rsformsApi = {
       }
     }),
   cstSubstitute: ({ itemID, data }: { itemID: LibraryItemID; data: ICstSubstitutions }) =>
-    axiosPatch<ICstSubstitutions, IRSFormData>({
+    axiosPatch<ICstSubstitutions, IRSFormDTO>({
       endpoint: `/api/rsforms/${itemID}/substitute`,
       request: {
         data: data,
@@ -184,7 +206,7 @@ export const rsformsApi = {
       }
     }),
   cstMove: ({ itemID, data }: { itemID: LibraryItemID; data: ICstMoveDTO }) =>
-    axiosPatch<ICstMoveDTO, IRSFormData>({
+    axiosPatch<ICstMoveDTO, IRSFormDTO>({
       endpoint: `/api/rsforms/${itemID}/move-cst`,
       request: { data: data }
     }),
@@ -198,7 +220,7 @@ export const rsformsApi = {
       }
     }),
   inlineSynthesis: ({ itemID, data }: { itemID: LibraryItemID; data: IInlineSynthesisDTO }) =>
-    axiosPost<IInlineSynthesisDTO, IRSFormData>({
+    axiosPost<IInlineSynthesisDTO, IRSFormDTO>({
       endpoint: `/api/rsforms/${itemID}/inline-synthesis`,
       request: {
         data: data,
@@ -206,12 +228,12 @@ export const rsformsApi = {
       }
     }),
   restoreOrder: ({ itemID }: { itemID: LibraryItemID }) =>
-    axiosPatch<undefined, IRSFormData>({
+    axiosPatch<undefined, IRSFormDTO>({
       endpoint: `/api/rsforms/${itemID}/restore-order`,
       request: { successMessage: information.reorderComplete }
     }),
   resetAliases: ({ itemID }: { itemID: LibraryItemID }) =>
-    axiosPatch<undefined, IRSFormData>({
+    axiosPatch<undefined, IRSFormDTO>({
       endpoint: `/api/rsforms/${itemID}/reset-aliases`,
       request: { successMessage: information.reindexComplete }
     }),
diff --git a/rsconcept/frontend/src/backend/rsform/useInlineSynthesis.tsx b/rsconcept/frontend/src/backend/rsform/useInlineSynthesis.tsx
index 4cb68644..69286841 100644
--- a/rsconcept/frontend/src/backend/rsform/useInlineSynthesis.tsx
+++ b/rsconcept/frontend/src/backend/rsform/useInlineSynthesis.tsx
@@ -4,9 +4,8 @@ import { DataCallback } from '@/backend/apiTransport';
 import { useUpdateTimestamp } from '@/backend/library/useUpdateTimestamp';
 import { ossApi } from '@/backend/oss/api';
 import { LibraryItemID } from '@/models/library';
-import { IRSFormData } from '@/models/rsform';
 
-import { IInlineSynthesisDTO, rsformsApi } from './api';
+import { IInlineSynthesisDTO, IRSFormDTO, rsformsApi } from './api';
 
 export const useInlineSynthesis = () => {
   const client = useQueryClient();
@@ -33,7 +32,7 @@ export const useInlineSynthesis = () => {
         itemID: LibraryItemID; //
         data: IInlineSynthesisDTO;
       },
-      onSuccess?: DataCallback<IRSFormData>
+      onSuccess?: DataCallback<IRSFormDTO>
     ) => mutation.mutate(data, { onSuccess })
   };
 };
diff --git a/rsconcept/frontend/src/backend/rsform/useRSForm.tsx b/rsconcept/frontend/src/backend/rsform/useRSForm.tsx
index ea7d03a0..b3313fae 100644
--- a/rsconcept/frontend/src/backend/rsform/useRSForm.tsx
+++ b/rsconcept/frontend/src/backend/rsform/useRSForm.tsx
@@ -1,7 +1,7 @@
 import { useQuery, useSuspenseQuery } from '@tanstack/react-query';
 
 import { LibraryItemID, VersionID } from '@/models/library';
-import { RSFormLoader } from '@/models/RSFormLoader';
+import { RSFormLoader } from '@/backend/rsform/RSFormLoader';
 
 import { queryClient } from '../queryClient';
 import { rsformsApi } from './api';
diff --git a/rsconcept/frontend/src/backend/rsform/useRSForms.tsx b/rsconcept/frontend/src/backend/rsform/useRSForms.tsx
index deb6804f..b93387f2 100644
--- a/rsconcept/frontend/src/backend/rsform/useRSForms.tsx
+++ b/rsconcept/frontend/src/backend/rsform/useRSForms.tsx
@@ -1,7 +1,7 @@
 import { useQueries } from '@tanstack/react-query';
 
 import { LibraryItemID } from '@/models/library';
-import { RSFormLoader } from '@/models/RSFormLoader';
+import { RSFormLoader } from '@/backend/rsform/RSFormLoader';
 
 import { DELAYS } from '../configuration';
 import { rsformsApi } from './api';
diff --git a/rsconcept/frontend/src/dialogs/DlgEditWordForms/DlgEditWordForms.tsx b/rsconcept/frontend/src/dialogs/DlgEditWordForms/DlgEditWordForms.tsx
index cbc84da2..c0261808 100644
--- a/rsconcept/frontend/src/dialogs/DlgEditWordForms/DlgEditWordForms.tsx
+++ b/rsconcept/frontend/src/dialogs/DlgEditWordForms/DlgEditWordForms.tsx
@@ -13,7 +13,7 @@ import Label from '@/components/ui/Label';
 import MiniButton from '@/components/ui/MiniButton';
 import Modal from '@/components/ui/Modal';
 import TextArea from '@/components/ui/TextArea';
-import { Grammeme, IWordForm, IWordFormPlain } from '@/models/language';
+import { Grammeme, IWordForm } from '@/models/language';
 import { parseGrammemes, wordFormEquals } from '@/models/languageAPI';
 import { HelpTopic } from '@/models/miscellaneous';
 import { IConstituenta, TermForm } from '@/models/rsform';
@@ -79,11 +79,13 @@ function DlgEditWordForms() {
   }
 
   function handleInflect() {
-    const data: IWordFormPlain = {
-      text: term,
-      grams: inputGrams.map(gram => gram.value).join(',')
-    };
-    inflectText(data, response => setInputText(response.result));
+    inflectText(
+      {
+        text: term,
+        grams: inputGrams.map(gram => gram.value).join(',')
+      },
+      response => setInputText(response.result)
+    );
   }
 
   function handleParse() {
diff --git a/rsconcept/frontend/src/models/language.ts b/rsconcept/frontend/src/models/language.ts
index 09c706b2..7dbc3811 100644
--- a/rsconcept/frontend/src/models/language.ts
+++ b/rsconcept/frontend/src/models/language.ts
@@ -214,21 +214,6 @@ export interface IWordForm {
   grams: GramData[];
 }
 
-/**
- * Represents wordform data used for backend communication.
- */
-export interface IWordFormPlain {
-  text: string;
-  grams: string;
-}
-
-/**
- * Represents lexeme response containing multiple {@link Wordform}s.
- */
-export interface ILexemeData {
-  items: IWordFormPlain[];
-}
-
 // ====== Reference resolution =====
 
 /**
@@ -270,11 +255,3 @@ export interface IReference {
   type: ReferenceType;
   data: IEntityReference | ISyntacticReference;
 }
-
-/**
- * Represents single resolved reference data.
- */
-export interface IResolvedReference extends IReference {
-  pos_input: ITextPosition;
-  pos_output: ITextPosition;
-}
diff --git a/rsconcept/frontend/src/models/oss.ts b/rsconcept/frontend/src/models/oss.ts
index 6f1100f6..f17e9491 100644
--- a/rsconcept/frontend/src/models/oss.ts
+++ b/rsconcept/frontend/src/models/oss.ts
@@ -42,11 +42,6 @@ export interface IOperation {
   arguments: OperationID[];
 }
 
-/**
- * Represents {@link IOperation} data from server.
- */
-export interface IOperationData extends Omit<IOperation, 'substitutions' | 'arguments'> {}
-
 /**
  * Represents {@link IOperation} position.
  */
@@ -115,20 +110,14 @@ export interface IOperationSchemaStats {
   count_owned: number;
 }
 
-/**
- * Represents backend data for {@link IOperationSchema}.
- */
-export interface IOperationSchemaData extends ILibraryItemData {
-  items: IOperationData[];
-  arguments: IArgument[];
-  substitutions: ICstSubstituteEx[];
-}
-
 /**
  * Represents OperationSchema.
  */
-export interface IOperationSchema extends IOperationSchemaData {
+export interface IOperationSchema extends ILibraryItemData {
   items: IOperation[];
+  arguments: IArgument[];
+  substitutions: ICstSubstituteEx[];
+
   graph: Graph;
   schemas: LibraryItemID[];
   stats: IOperationSchemaStats;
diff --git a/rsconcept/frontend/src/models/ossAPI.ts b/rsconcept/frontend/src/models/ossAPI.ts
index 24e4f30b..3047b505 100644
--- a/rsconcept/frontend/src/models/ossAPI.ts
+++ b/rsconcept/frontend/src/models/ossAPI.ts
@@ -2,6 +2,7 @@
  * Module: API for OperationSystem.
  */
 
+import { ConstituentaID, CstClass, CstType, IConstituenta, IRSForm } from '@/models/rsform';
 import { limits } from '@/utils/constants';
 import { describeSubstitutionError, information } from '@/utils/labels';
 import { TextMatcher } from '@/utils/utils';
@@ -9,7 +10,6 @@ import { TextMatcher } from '@/utils/utils';
 import { Graph } from './Graph';
 import { ILibraryItem, LibraryItemID } from './library';
 import { ICstSubstitute, IOperation, IOperationSchema, OperationID, SubstitutionErrorType } from './oss';
-import { ConstituentaID, CstClass, CstType, IConstituenta, IRSForm } from './rsform';
 import { AliasMapping, ParsingStatus } from './rslang';
 import { applyAliasMapping, applyTypificationMapping, extractGlobals, isSetTypification } from './rslangAPI';
 
@@ -49,7 +49,6 @@ export function sortItemsForOSS(oss: IOperationSchema, items: ILibraryItem[]): I
 
 type CrossMapping = Map<LibraryItemID, AliasMapping>;
 
-// TODO: test validator
 /**
  * Validator for Substitution table.
  */
@@ -459,7 +458,6 @@ export function getRelocateCandidates(
       const original = oss.substitutions.find(sub => sub.substitution === parent)?.original;
       if (original) {
         continue;
-        // TODO: test if original schema is destination schema
       }
     }
     unreachableBases.push(cst.id);
diff --git a/rsconcept/frontend/src/models/rsform.ts b/rsconcept/frontend/src/models/rsform.ts
index 5abb8f3d..e27963ba 100644
--- a/rsconcept/frontend/src/models/rsform.ts
+++ b/rsconcept/frontend/src/models/rsform.ts
@@ -83,9 +83,9 @@ export interface ITargetCst {
 }
 
 /**
- * Represents {@link IConstituenta} data from server.
+ * Represents Constituenta.
  */
-export interface IConstituentaData extends IConstituentaMeta {
+export interface IConstituenta extends IConstituentaMeta {
   parse: {
     status: ParsingStatus;
     valueClass: ValueClass;
@@ -93,12 +93,7 @@ export interface IConstituentaData extends IConstituentaMeta {
     syntaxTree: string;
     args: IArgumentInfo[];
   };
-}
 
-/**
- * Represents Constituenta.
- */
-export interface IConstituenta extends IConstituentaData {
   /** {@link LibraryItemID} of this {@link IConstituenta}. */
   schema: LibraryItemID;
 
@@ -172,27 +167,21 @@ export interface IRSFormStats {
 /**
  * Represents inheritance data for {@link IRSForm}.
  */
-export interface IInheritanceData {
+export interface IInheritanceInfo {
   child: ConstituentaID;
   child_source: LibraryItemID;
   parent: ConstituentaID;
   parent_source: LibraryItemID;
 }
 
-/**
- * Represents data for {@link IRSForm} provided by backend.
- */
-export interface IRSFormData extends ILibraryItemVersioned {
-  items: IConstituentaData[];
-  inheritance: IInheritanceData[];
-  oss: ILibraryItemReference[];
-}
-
 /**
  * Represents formal explication for set of concepts.
  */
-export interface IRSForm extends IRSFormData {
+export interface IRSForm extends ILibraryItemVersioned {
   items: IConstituenta[];
+  inheritance: IInheritanceInfo[];
+  oss: ILibraryItemReference[];
+
   stats: IRSFormStats;
   graph: Graph;
   cstByAlias: Map<string, IConstituenta>;