diff --git a/src/main/java/de/hsel/itech/db/Database.java b/src/main/java/de/hsel/itech/db/Database.java
index 9243490..4e3c60a 100644
--- a/src/main/java/de/hsel/itech/db/Database.java
+++ b/src/main/java/de/hsel/itech/db/Database.java
@@ -30,6 +30,12 @@ import java.util.Map;
  */
 public class Database {
 
+    private final String BOOK = "book";
+    private final String AUTHOR = "author";
+    private final String AUTHOR_BOOK = "author_book";
+    private final String PUBLISHER = "publisher";
+    private final String CATEGORY = "category";
+
     private static Database instance;
 
     public static Database getInstance() {
@@ -100,7 +106,7 @@ public class Database {
 
     @Nullable
     public Author getAuthor(long id) {
-        Map.Entry<ResultSet, Connection> entry = getResultSet(id, "author");
+        Map.Entry<ResultSet, Connection> entry = getResultSet(id, AUTHOR);
         assert entry != null;
 
         ResultSet rs = entry.getKey();
@@ -116,7 +122,7 @@ public class Database {
 
     @Nullable
     public Category getCategory(long id) {
-        Map.Entry<ResultSet, Connection> entry = getResultSet(id, "category");
+        Map.Entry<ResultSet, Connection> entry = getResultSet(id, CATEGORY);
         assert entry != null;
 
         ResultSet rs = entry.getKey();
@@ -132,7 +138,7 @@ public class Database {
 
     @Nullable
     public Publisher getPublisher(long id) {
-        Map.Entry<ResultSet, Connection> entry = getResultSet(id, "category");
+        Map.Entry<ResultSet, Connection> entry = getResultSet(id, PUBLISHER);
         assert entry != null;
 
         ResultSet rs = entry.getKey();
@@ -148,12 +154,12 @@ public class Database {
 
     @Nullable
     private List<Integer> getAuthors(long id) {
-        Map.Entry<List<ResultSet>, Connection> entry = getResultSets(id, "author_book", "book");
+        Map.Entry<List<ResultSet>, Connection> entry = getResultSets(id, AUTHOR_BOOK, BOOK);
         assert entry != null;
         try {
             List<Integer> list = new ArrayList<>();
             for (ResultSet rs : entry.getKey()) {
-                list.add(rs.getInt("author"));
+                list.add(rs.getInt(AUTHOR));
             }
             entry.getValue().close();
             return list;
@@ -165,14 +171,14 @@ public class Database {
 
     @Nullable
     public Book getBook(long id) {
-        Map.Entry<ResultSet, Connection> entry = getResultSet(id, "book");
+        Map.Entry<ResultSet, Connection> entry = getResultSet(id, BOOK);
         assert entry != null;
 
         ResultSet rs = entry.getKey();
         Book book = null;
         try {
-            Category category = getCategory(rs.getLong("category"));
-            Publisher publisher = getPublisher(rs.getLong("publisher"));
+            Category category = getCategory(rs.getLong(CATEGORY));
+            Publisher publisher = getPublisher(rs.getLong(PUBLISHER));
             List<Integer> authorIds = getAuthors(id);
             assert authorIds != null;
             List<Author> authors = new ArrayList<>();
@@ -191,7 +197,7 @@ public class Database {
 
     @Nullable
     public List<Book> getBooks() {
-        Map.Entry<List<ResultSet>, Connection> entry = getResultSets("book", "id");
+        Map.Entry<List<ResultSet>, Connection> entry = getResultSets(BOOK, "id");
         assert entry != null;
 
         List<Long> ids = new ArrayList<>();
@@ -298,7 +304,6 @@ public class Database {
         }catch (SQLException ex) {
             ex.printStackTrace();
         }
-
         return insertCount;
     }
 
@@ -322,11 +327,90 @@ public class Database {
         }catch (SQLException ex) {
             ex.printStackTrace();
         }
-
-
         return insertCount;
     }
 
+    /**
+     * inserts Publisher
+     * @param publisher Publisher
+     * @return insert count
+     */
+    public int insert(@NotNull Publisher publisher) {
+        Connection connection = getConnection();
+        assert connection != null;
+
+        int insertCount = 0;
+        try{
+            PreparedStatement statement = connection.prepareStatement("INSERT INTO publisher (name) VALUES (?)");
+            statement.setString(1, publisher.getName());
+
+            insertCount += statement.executeUpdate();
+
+            connection.close();
+        }catch (SQLException ex) {
+            ex.printStackTrace();
+        }
+        return insertCount;
+    }
+
+    public int deleteBook(long id) {
+        int deleteCount = 0;
+
+        try{
+            Connection connection = getConnection();
+            assert connection != null;
+
+            PreparedStatement statement = connection.prepareStatement("DELETE FROM author_book WHERE book = ?");
+            statement.setLong(1, id);
+            deleteCount =+ statement.executeUpdate();
+
+            connection.close();
+        }catch (SQLException ex) {
+            ex.printStackTrace();
+        }
+
+        deleteCount += delete(id, BOOK);
+
+        return deleteCount;
+    }
+
+    public int deleteAuthor(long id) {
+        return delete(id, AUTHOR);
+    }
+
+    public int deletePublisher(long id) {
+        return delete(id, PUBLISHER);
+    }
+
+    public int deleteCategory(long id) {
+        return delete(id, CATEGORY);
+    }
+
+
+
+    /**
+     *
+     * @param id
+     * @param table
+     * @return delete count
+     */
+    private int delete(long id, String table) {
+        Connection connection = getConnection();
+        assert connection != null;
+
+        int deleteCount = 0;
+        try{
+            PreparedStatement statement = connection.prepareStatement("DELETE FROM ? WHERE id=?");
+            statement.setString(1, table);
+            statement.setLong(2, id);
+
+            deleteCount =+ statement.executeUpdate();
+
+        }catch (SQLException ex) {
+            ex.printStackTrace();
+        }
+        return deleteCount;
+    }
 
 
 
@@ -351,19 +435,8 @@ public class Database {
         return null;
     }
 
-    @NotNull
-    private Map.Entry<List<ResultSet>, Connection> getListConnectionEntry(Connection connection, PreparedStatement statement) throws SQLException {
-        ResultSet resultSet = statement.executeQuery();
-
-        Map.Entry<List<ResultSet>, Connection> entry = new AbstractMap.SimpleEntry<>(new ArrayList<>(), connection);
-        while (resultSet.next()) {
-            entry.getKey().add(resultSet);
-        }
-        return entry;
-    }
-
     @Nullable
-    private Map.Entry<List<ResultSet>, Connection> getResultSets(long id, String table, String column) {
+    private Map.Entry<List<ResultSet>, Connection> getResultSets(long id, @NotNull String table, @NotNull String column) {
         Connection connection = getConnection();
         try {
             assert connection != null;
@@ -380,7 +453,7 @@ public class Database {
     }
 
     @Nullable
-    private Map.Entry<List<ResultSet>, Connection> getResultSets(String table, String columns) {
+    private Map.Entry<List<ResultSet>, Connection> getResultSets(@NotNull String table, @NotNull String columns) {
         Connection connection = getConnection();
         try {
             assert connection != null;
@@ -395,4 +468,14 @@ public class Database {
         return null;
     }
 
+    @NotNull
+    private Map.Entry<List<ResultSet>, Connection> getListConnectionEntry(@NotNull Connection connection, @NotNull PreparedStatement statement) throws SQLException {
+        ResultSet resultSet = statement.executeQuery();
+
+        Map.Entry<List<ResultSet>, Connection> entry = new AbstractMap.SimpleEntry<>(new ArrayList<>(), connection);
+        while (resultSet.next()) {
+            entry.getKey().add(resultSet);
+        }
+        return entry;
+    }
 }
\ No newline at end of file