diff --git a/webseite/classes/Config.php b/webseite/classes/Config.php
new file mode 100644
index 0000000..27e6f42
--- /dev/null
+++ b/webseite/classes/Config.php
@@ -0,0 +1,51 @@
+<?php
+
+/**
+ * Konfigurationsdaten
+ */
+class Config
+{
+    /**
+     * @return string Verzeichnis für generelle Konfigurationsdaten
+     */
+    public static function getConfigDirectory(): string
+    {
+        return "config/";
+    }
+
+    /**
+     * @return string Verzeichnis für Fächer
+     */
+    public static function getSubjectsDirectory(): string
+    {
+        return self::getConfigDirectory() . "subjects/";
+    }
+
+    /**
+     * @param string $subjectId ID des Faches
+     * @return string Verzeichnis des Faches
+     */
+    public static function getSubjectDirectory(string $subjectId): string
+    {
+        return self::getSubjectsDirectory() . $subjectId . "/";
+    }
+
+    /**
+     * @param string $subjectId ID des Faches
+     * @return string Verzeichnis der Themen des Faches
+     */
+    public static function getTopicsDirectory(string $subjectId): string
+    {
+        return self::getSubjectDirectory($subjectId) . "topics/";
+    }
+
+    /**
+     * @param string $subjectId ID des Faches
+     * @param string $topicId ID des Themas
+     * @return string Verzeichnis des Themas
+     */
+    public static function getTopicDirectory(string $subjectId, string $topicId): string
+    {
+        return self::getTopicsDirectory($subjectId) . $topicId . "/";
+    }
+}
\ No newline at end of file
diff --git a/webseite/classes/SubjectData.php b/webseite/classes/SubjectData.php
index 71bbd27..82e6196 100644
--- a/webseite/classes/SubjectData.php
+++ b/webseite/classes/SubjectData.php
@@ -1,9 +1,10 @@
 <?php
+require_once("Config.php");
 require_once("Util.php");
 require_once("TopicData.php");
 
 /**
- * Stellt alle relevanten Daten für ein einzeles Fach bereit
+ * Stellt alle relevanten Daten für ein einzelnes Fach bereit
  *
  */
 class SubjectData
@@ -47,8 +48,7 @@ class SubjectData
     {
         $result = array();
 
-        $subjectDirectory = "config/subjects";
-        $subjectNames = scandir($subjectDirectory);
+        $subjectNames = scandir(Config::getSubjectsDirectory());
 
         usort($subjectNames, function ($a, $b) {
             return strcmp($a, $b);
@@ -79,10 +79,11 @@ class SubjectData
     {
         $result = new SubjectData();
 
-        $subjectId = Util::removeIllegalCharacters($subjectId);
+        if (Util::containsIllegalCharacters($subjectId)) {
+            return null;
+        }
 
-        $subjectDirectory = "config/subjects/$subjectId";
-        $filename = "$subjectDirectory/properties.json";
+        $filename = Config::getSubjectDirectory($subjectId) . "properties.json";
         $data = Util::parseJsonFromFile($filename);
         if (!isset($data)) {
             return null;
diff --git a/webseite/classes/TopicData.php b/webseite/classes/TopicData.php
index 66bbac4..65f1f17 100644
--- a/webseite/classes/TopicData.php
+++ b/webseite/classes/TopicData.php
@@ -1,4 +1,5 @@
 <?php
+require_once("Config.php");
 require_once("Util.php");
 
 class TopicData
@@ -52,8 +53,7 @@ class TopicData
     {
         $result = array();
 
-        $topicDirectory = "config/subjects/$subjectId/topics";
-        $topicNames = scandir($topicDirectory);
+        $topicNames = scandir(Config::getTopicsDirectory($subjectId));
 
         usort($topicNames, function ($a, $b) {
             return strcmp($a, $b);
@@ -87,9 +87,7 @@ class TopicData
         $subjectId = Util::removeIllegalCharacters($subjectId);
         $topicId = Util::removeIllegalCharacters($topicId);
 
-        $topicsDirectory = "config/subjects/$subjectId/topics";
-        $topicDataDirectory = "$topicsDirectory/$topicId";
-        $data = Util::parseJsonFromFile("$topicDataDirectory/properties.json");
+        $data = Util::parseJsonFromFile(Config::getTopicDirectory($subjectId, $topicId) . "properties.json");
         if (!isset($data)) {
             return null;
         }
@@ -126,15 +124,14 @@ class TopicData
             $result->files = array();
         }
 
-        $article = Util::readFileContent("$topicDataDirectory/article.html");
+        $article = Util::readFileContent(Config::getTopicDirectory($subjectId, $topicId) . "article.html");
         if (!isset($article)) {
             $article = "Kein Erklärtext vorhanden";
         }
-        $article = str_replace('$TOPICPATH', $topicDataDirectory, $article);
+        $article = str_replace('$TOPICPATH', Config::getTopicDirectory($subjectId, $topicId), $article);
 
         $result->article = $article;
 
         return $result;
     }
-
 }
\ No newline at end of file