diff --git a/src/knowledge_base.cpp b/src/knowledge_base.cpp
index 2f1e82e..6a53f2e 100644
--- a/src/knowledge_base.cpp
+++ b/src/knowledge_base.cpp
@@ -93,7 +93,7 @@ void obelisk::KnowledgeBase::addEntities(std::vector<obelisk::Entity>& entities)
         {
             entity.insertEntity(dbConnection_);
         }
-        catch (obelisk::DatabaseException::ConstraintException& exception)
+        catch (obelisk::DatabaseConstraintException& exception)
         {
             // ignore unique constraint error
             if (std::strcmp(exception.what(),
@@ -114,7 +114,7 @@ void obelisk::KnowledgeBase::addVerbs(std::vector<obelisk::Verb>& verbs)
         {
             verb.insertVerb(dbConnection_);
         }
-        catch (obelisk::DatabaseException::ConstraintException& exception)
+        catch (obelisk::DatabaseConstraintException& exception)
         {
             // ignore unique constraint error
             if (std::strcmp(exception.what(),
@@ -135,7 +135,7 @@ void obelisk::KnowledgeBase::addFacts(std::vector<obelisk::Fact>& facts)
         {
             fact.insertFact(dbConnection_);
         }
-        catch (obelisk::DatabaseException::ConstraintException& exception)
+        catch (obelisk::DatabaseConstraintException& exception)
         {
             // ignore unique constraint error
             if (std::strcmp(exception.what(),
diff --git a/src/models/entity.cpp b/src/models/entity.cpp
index d7e81a8..159cf46 100644
--- a/src/models/entity.cpp
+++ b/src/models/entity.cpp
@@ -38,13 +38,13 @@ void obelisk::Entity::selectEntity(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -62,10 +62,10 @@ void obelisk::Entity::selectEntity(sqlite3* dbConnection)
             setName((char*) sqlite3_column_text(ppStmt, 1));
             break;
         case SQLITE_BUSY :
-            throw obelisk::DatabaseException::BusyException();
+            throw obelisk::DatabaseBusyException();
             break;
         case SQLITE_MISUSE :
-            throw obelisk::DatabaseException::MisuseException();
+            throw obelisk::DatabaseMisuseException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -106,13 +106,13 @@ void obelisk::Entity::insertEntity(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -127,13 +127,13 @@ void obelisk::Entity::insertEntity(sqlite3* dbConnection)
             sqlite3_set_last_insert_rowid(dbConnection, 0);
             break;
         case SQLITE_CONSTRAINT :
-            throw obelisk::DatabaseException::ConstraintException(
+            throw obelisk::DatabaseConstraintException(
                 sqlite3_errmsg(dbConnection));
         case SQLITE_BUSY :
-            throw obelisk::DatabaseException::BusyException();
+            throw obelisk::DatabaseBusyException();
             break;
         case SQLITE_MISUSE :
-            throw obelisk::DatabaseException::MisuseException();
+            throw obelisk::DatabaseMisuseException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
diff --git a/src/models/error.h b/src/models/error.h
index e8ace1b..7c733c2 100644
--- a/src/models/error.h
+++ b/src/models/error.h
@@ -8,8 +8,8 @@ namespace obelisk
 {
     class DatabaseException : public std::exception
     {
-        private:
-            const std::string errorMessage_;
+        protected:
+            std::string errorMessage_;
 
         public:
             DatabaseException() :
@@ -28,118 +28,76 @@ namespace obelisk
             {
             }
 
-            const char* what() const noexcept
+            virtual const char* what() const noexcept
             {
                 return errorMessage_.c_str();
             }
 
-            class SizeException : public std::exception
+            virtual void setErrorMessage(const std::string errorMessage)
             {
-                private:
-                    const std::string errorMessage_;
+                errorMessage_ = errorMessage;
+            }
+    };
 
-                public:
-                    SizeException() :
-                        errorMessage_("size of string or blob exceeds limits")
-                    {
-                    }
-
-                    const char* what() const noexcept
-                    {
-                        return errorMessage_.c_str();
-                    }
-            };
-
-            class RangeException : public std::exception
+    class DatabaseSizeException : public obelisk::DatabaseException
+    {
+        public:
+            DatabaseSizeException()
             {
-                private:
-                    const std::string errorMessage_;
+                setErrorMessage("size of string or blob exceeds limits");
+            }
+    };
 
-                public:
-                    RangeException() :
-                        errorMessage_("parameter index is out of range")
-                    {
-                    }
-
-                    const char* what() const noexcept
-                    {
-                        return errorMessage_.c_str();
-                    }
-            };
-
-            class MemoryException : public std::exception
+    class DatabaseRangeException : public obelisk::DatabaseException
+    {
+        public:
+            DatabaseRangeException()
             {
-                private:
-                    const std::string errorMessage_;
+                setErrorMessage("parameter index is out of range");
+            }
+    };
 
-                public:
-                    MemoryException() :
-                        errorMessage_("not enough memory for operation")
-                    {
-                    }
-
-                    const char* what() const noexcept
-                    {
-                        return errorMessage_.c_str();
-                    }
-            };
-
-            class BusyException : public std::exception
+    class DatabaseMemoryException : public obelisk::DatabaseException
+    {
+        public:
+            DatabaseMemoryException()
             {
-                private:
-                    const std::string errorMessage_;
+                setErrorMessage("not enough memory for operation");
+            }
+    };
 
-                public:
-                    BusyException() :
-                        errorMessage_(
-                            "database was busy and operation not performed")
-                    {
-                    }
-
-                    const char* what() const noexcept
-                    {
-                        return errorMessage_.c_str();
-                    }
-            };
-
-            class MisuseException : public std::exception
+    class DatabaseBusyException : public obelisk::DatabaseException
+    {
+        public:
+            DatabaseBusyException()
             {
-                private:
-                    const std::string errorMessage_;
+                setErrorMessage(
+                    "database was busy and operation was not performed");
+            }
+    };
 
-                public:
-                    MisuseException() :
-                        errorMessage_("misuse of the database routine")
-                    {
-                    }
+    class DatabaseMisuseException : public obelisk::DatabaseException
+    {
+        public:
+            DatabaseMisuseException()
 
-                    const char* what() const noexcept
-                    {
-                        return errorMessage_.c_str();
-                    }
-            };
-
-            class ConstraintException : public std::exception
             {
-                private:
-                    const std::string errorMessage_;
+                setErrorMessage("misuse of the database routine");
+            }
+    };
 
-                public:
-                    ConstraintException() :
-                        errorMessage_("a constraint exception occurred")
-                    {
-                    }
+    class DatabaseConstraintException : public obelisk::DatabaseException
+    {
+        public:
+            DatabaseConstraintException()
+            {
+                setErrorMessage("a constraint exception occurred");
+            }
 
-                    ConstraintException(const std::string& errorMessage) :
-                        errorMessage_(errorMessage)
-                    {
-                    }
-
-                    const char* what() const noexcept
-                    {
-                        return errorMessage_.c_str();
-                    }
-            };
+            DatabaseConstraintException(const std::string& errorMessage)
+            {
+                setErrorMessage(errorMessage);
+            }
     };
 } // namespace obelisk
 
diff --git a/src/models/fact.cpp b/src/models/fact.cpp
index 467373d..75f0058 100644
--- a/src/models/fact.cpp
+++ b/src/models/fact.cpp
@@ -43,13 +43,13 @@ void obelisk::Fact::selectFact(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -62,13 +62,13 @@ void obelisk::Fact::selectFact(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -81,13 +81,13 @@ void obelisk::Fact::selectFact(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -107,10 +107,10 @@ void obelisk::Fact::selectFact(sqlite3* dbConnection)
             getVerb().setId(sqlite3_column_int(ppStmt, 3));
             break;
         case SQLITE_BUSY :
-            throw obelisk::DatabaseException::BusyException();
+            throw obelisk::DatabaseBusyException();
             break;
         case SQLITE_MISUSE :
-            throw obelisk::DatabaseException::MisuseException();
+            throw obelisk::DatabaseMisuseException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -149,13 +149,13 @@ void obelisk::Fact::insertFact(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -168,13 +168,13 @@ void obelisk::Fact::insertFact(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -187,13 +187,13 @@ void obelisk::Fact::insertFact(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -208,13 +208,13 @@ void obelisk::Fact::insertFact(sqlite3* dbConnection)
             sqlite3_set_last_insert_rowid(dbConnection, 0);
             break;
         case SQLITE_CONSTRAINT :
-            throw obelisk::DatabaseException::ConstraintException(
+            throw obelisk::DatabaseConstraintException(
                 sqlite3_errmsg(dbConnection));
         case SQLITE_BUSY :
-            throw obelisk::DatabaseException::BusyException();
+            throw obelisk::DatabaseBusyException();
             break;
         case SQLITE_MISUSE :
-            throw obelisk::DatabaseException::MisuseException();
+            throw obelisk::DatabaseMisuseException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
diff --git a/src/models/verb.cpp b/src/models/verb.cpp
index 9649533..778d89a 100644
--- a/src/models/verb.cpp
+++ b/src/models/verb.cpp
@@ -39,13 +39,13 @@ void obelisk::Verb::selectVerb(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -63,10 +63,10 @@ void obelisk::Verb::selectVerb(sqlite3* dbConnection)
             setName((char*) sqlite3_column_text(ppStmt, 1));
             break;
         case SQLITE_BUSY :
-            throw obelisk::DatabaseException::BusyException();
+            throw obelisk::DatabaseBusyException();
             break;
         case SQLITE_MISUSE :
-            throw obelisk::DatabaseException::MisuseException();
+            throw obelisk::DatabaseMisuseException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -106,13 +106,13 @@ void obelisk::Verb::insertVerb(sqlite3* dbConnection)
         case SQLITE_OK :
             break;
         case SQLITE_TOOBIG :
-            throw obelisk::DatabaseException::SizeException();
+            throw obelisk::DatabaseSizeException();
             break;
         case SQLITE_RANGE :
-            throw obelisk::DatabaseException::RangeException();
+            throw obelisk::DatabaseRangeException();
             break;
         case SQLITE_NOMEM :
-            throw obelisk::DatabaseException::MemoryException();
+            throw obelisk::DatabaseMemoryException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));
@@ -127,13 +127,13 @@ void obelisk::Verb::insertVerb(sqlite3* dbConnection)
             sqlite3_set_last_insert_rowid(dbConnection, 0);
             break;
         case SQLITE_CONSTRAINT :
-            throw obelisk::DatabaseException::ConstraintException(
+            throw obelisk::DatabaseConstraintException(
                 sqlite3_errmsg(dbConnection));
         case SQLITE_BUSY :
-            throw obelisk::DatabaseException::BusyException();
+            throw obelisk::DatabaseBusyException();
             break;
         case SQLITE_MISUSE :
-            throw obelisk::DatabaseException::MisuseException();
+            throw obelisk::DatabaseMisuseException();
             break;
         default :
             throw obelisk::DatabaseException(sqlite3_errmsg(dbConnection));