diff --git a/src/entities/entities.ts b/src/entities/entities.ts
index 79acaae..4f1f1dc 100644
--- a/src/entities/entities.ts
+++ b/src/entities/entities.ts
@@ -1,6 +1,6 @@
 export interface IEntityWithIdAndOptionalTimestamp {
   id: string;
-  millisecondsSinceEpoch: number;
+  millisecondsSinceEpoch?: number;
 }
 
 export interface ISystem extends IEntityWithIdAndOptionalTimestamp {
diff --git a/src/loaders/RepositoryDataLoader.ts b/src/loaders/RepositoryDataLoader.ts
index f229843..fab71b9 100644
--- a/src/loaders/RepositoryDataLoader.ts
+++ b/src/loaders/RepositoryDataLoader.ts
@@ -1,4 +1,5 @@
-import { IOrderedStop, IRoute, IShuttle, IStop, ISystem, GetterSetterRepository } from "../repositories/GetterSetterRepository";
+import { GetterSetterRepository } from "../repositories/GetterSetterRepository";
+import { IRoute, IShuttle, IStop, ISystem } from "../entities/entities";
 
 const timeout = 10000;
 const systemIdsToSupport = ["263"];
diff --git a/src/loaders/loadTestData.ts b/src/loaders/loadTestData.ts
index 8fce9c9..9e83e8a 100644
--- a/src/loaders/loadTestData.ts
+++ b/src/loaders/loadTestData.ts
@@ -1,5 +1,6 @@
 // Mock data
-import { IEta, IOrderedStop, IRoute, IShuttle, IStop, ISystem, GetterSetterRepository } from "../repositories/GetterSetterRepository";
+import { IEta, IOrderedStop, IRoute, IShuttle, IStop, ISystem } from "../entities/entities";
+import { GetterSetterRepository } from "../repositories/GetterSetterRepository";
 
 const systems: ISystem[] = [
   {
diff --git a/src/repositories/ApiBasedRepository.ts b/src/repositories/ApiBasedRepository.ts
new file mode 100644
index 0000000..51ebf12
--- /dev/null
+++ b/src/repositories/ApiBasedRepository.ts
@@ -0,0 +1,68 @@
+import { GetterRepository } from "./GetterRepository";
+import { IEta } from "../entities/entities";
+
+export class ApiBasedRepository implements GetterRepository {
+  public async getEtaForShuttleAndStopId(shuttleId: string, stopId: string): Promise<IEta | null> {
+    // TODO: implement
+
+    return null;
+  }
+
+  public async getEtasForShuttleId(shuttleId: string): Promise<[]> {
+    // TODO: implement
+
+    return [];
+  }
+
+  public async getEtasForStopId(stopId: string): Promise<[]> {
+    return [];
+  }
+
+  public async getOrderedStopByRouteAndStopId(routeId: string, stopId: string): Promise<| null> {
+    return null;
+  }
+
+  public async getOrderedStopsByRouteId(routeId: string): Promise<[]> {
+    return Promise.resolve([]);
+  }
+
+  public async getOrderedStopsByStopId(stopId: string): Promise<[]> {
+    return Promise.resolve([]);
+  }
+
+  public async getRouteById(routeId: string): Promise<| null> {
+    return Promise.resolve(null);
+  }
+
+  public async getRoutesBySystemId(systemId: string): Promise<[]> {
+    return Promise.resolve([]);
+  }
+
+  public async getShuttleById(shuttleId: string): Promise<| null> {
+    return Promise.resolve(null);
+  }
+
+  public async getShuttlesByRouteId(routeId: string): Promise<[]> {
+    return Promise.resolve([]);
+  }
+
+  public async getShuttlesBySystemId(systemId: string): Promise<[]> {
+    return Promise.resolve([]);
+  }
+
+  public async getStopById(stopId: string): Promise<| null> {
+    return null;
+  }
+
+  public async getStopsBySystemId(systemId: string): Promise<[]> {
+    return [];
+  }
+
+  public async getSystemById(systemId: string): Promise<| null> {
+    return null;
+  }
+
+  public async getSystems(): Promise<[]> {
+    return Promise.resolve([]);
+  }
+}
\ No newline at end of file
diff --git a/src/repositories/GetterRepository.ts b/src/repositories/GetterRepository.ts
index 5d62dbd..4c6a3b0 100644
--- a/src/repositories/GetterRepository.ts
+++ b/src/repositories/GetterRepository.ts
@@ -1,4 +1,4 @@
-import { IEta, IOrderedStop, IRoute, IShuttle, IStop, ISystem } from "./GetterSetterRepository";
+import { IEta, IOrderedStop, IRoute, IShuttle, IStop, ISystem } from "../entities/entities";
 
 export interface GetterRepository {
   getSystems(): Promise<ISystem[]>;
diff --git a/src/repositories/UnoptimizedInMemoryRepository.ts b/src/repositories/UnoptimizedInMemoryRepository.ts
index ad47221..60a8773 100644
--- a/src/repositories/UnoptimizedInMemoryRepository.ts
+++ b/src/repositories/UnoptimizedInMemoryRepository.ts
@@ -1,4 +1,13 @@
-import { IEntityWithId, IEta, IOrderedStop, IRoute, IShuttle, IStop, ISystem, GetterSetterRepository } from "./GetterSetterRepository";
+import { GetterSetterRepository } from "./GetterSetterRepository";
+import {
+  IEntityWithIdAndOptionalTimestamp,
+  IEta,
+  IOrderedStop,
+  IRoute,
+  IShuttle,
+  IStop,
+  ISystem
+} from "../entities/entities";
 
 /**
  * An unoptimized in memory repository.
@@ -73,7 +82,7 @@ export class UnoptimizedInMemoryRepository implements GetterSetterRepository {
     return this.orderedStops.filter((value) => value.routeId === routeId);
   }
 
-  private findEntityById<T extends IEntityWithId>(entityId: string, arrayToSearchIn: T[]) {
+  private findEntityById<T extends IEntityWithIdAndOptionalTimestamp>(entityId: string, arrayToSearchIn: T[]) {
     return this.findEntityByMatcher((value) => value.id === entityId, arrayToSearchIn);
   }