diff --git a/Admin/Install/Media/bill.pdf.php b/Admin/Install/Media/bill.pdf.php
index e2895b1..4b29464 100755
--- a/Admin/Install/Media/bill.pdf.php
+++ b/Admin/Install/Media/bill.pdf.php
@@ -25,7 +25,7 @@ $bill = $this->getData('bill') ?? new NullBill();
 
 // Set up default pdf template
 /** @phpstan-import-type DefaultPdf from ../../../../Admin/Install/Media/PdfDefaultTemplate/pdfTemplate.pdf.php */
-$pdf = new DefaultPdf('P', 'mm', 'A4', true, 'UTF-8', false);
+$pdf = new DefaultPdf();
 
 $lang = include __DIR__ . '/lang.php';
 
diff --git a/Admin/Install/Media/lang.php b/Admin/Install/Media/lang.php
index 252fa3e..a5ae0f2 100644
--- a/Admin/Install/Media/lang.php
+++ b/Admin/Install/Media/lang.php
@@ -1,5 +1,17 @@
 <?php
-
+/**
+ * Karaka
+ *
+ * PHP Version 8.1
+ *
+ * Bill localization.
+ *
+ * @package   Modules\Media
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 2.0
+ * @version   1.0.0
+ * @link      https://jingga.app
+ */
 declare(strict_types=1);
 
 return [
diff --git a/Admin/Installer.php b/Admin/Installer.php
index bc1fec8..fa144ce 100755
--- a/Admin/Installer.php
+++ b/Admin/Installer.php
@@ -14,9 +14,9 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Admin;
 
+use Modules\Attribute\Models\AttributeTypeMapper;
 use Modules\Billing\Models\BillTransferType;
 use Modules\ClientManagement\Models\ClientAttributeTypeMapper;
-use Modules\ItemManagement\Models\ItemAttributeTypeMapper;
 use Modules\SupplierManagement\Models\SupplierAttributeTypeMapper;
 use phpOMS\Application\ApplicationAbstract;
 use phpOMS\Config\SettingsInterface;
@@ -243,26 +243,26 @@ final class Installer extends InstallerAbstract
         /** @var \Modules\Billing\Controller\ApiController $module */
         $module = $app->moduleManager->getModuleInstance('Billing');
 
-        /** @var \Modules\ItemManagement\Models\ItemAttributeType $itemAttributeSales */
-        $itemAttributeSales = ItemAttributeTypeMapper::get()
+        /** @var \Modules\Attribute\Models\AttributeType $AttributeSales */
+        $AttributeSales = AttributeTypeMapper::get()
             ->with('defaults')
             ->where('name', 'sales_tax_code')
             ->execute();
 
-        /** @var \Modules\ClientManagement\Models\ClientAttributeType $clientAttributeSales */
+        /** @var \Modules\Attribute\Models\AttributeType $clientAttributeSales */
         $clientAttributeSales = ClientAttributeTypeMapper::get()
             ->with('defaults')
             ->where('name', 'sales_tax_code')
             ->execute();
 
-        /** @var \Modules\SupplierManagement\Models\SupplierAttributeType $supplierAttributeSales */
+        /** @var \Modules\Attribute\Models\AttributeType $supplierAttributeSales */
         $supplierAttributeSales = SupplierAttributeTypeMapper::get()
             ->with('defaults')
             ->where('name', 'purchase_tax_code')
             ->execute();
 
         foreach ($taxes as $tax) {
-            $itemValue    = $itemAttributeSales->getDefaultByValue($tax['item_code']);
+            $itemValue    = $AttributeSales->getDefaultByValue($tax['item_code']);
             $accountValue = $tax['type'] === 1
                 ? $clientAttributeSales->getDefaultByValue($tax['account_code'])
                 : $supplierAttributeSales->getDefaultByValue($tax['account_code']);
diff --git a/Controller/ApiAttributeController.php b/Controller/ApiAttributeController.php
index f2bc070..e2f4395 100755
--- a/Controller/ApiAttributeController.php
+++ b/Controller/ApiAttributeController.php
@@ -14,16 +14,16 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Controller;
 
-use Modules\Billing\Models\Attribute\BillAttribute;
+use Modules\Attribute\Models\Attribute;
+use Modules\Attribute\Models\AttributeType;
+use Modules\Attribute\Models\AttributeValue;
+use Modules\Attribute\Models\NullAttributeType;
+use Modules\Attribute\Models\NullAttributeValue;
 use Modules\Billing\Models\Attribute\BillAttributeMapper;
-use Modules\Billing\Models\Attribute\BillAttributeType;
 use Modules\Billing\Models\Attribute\BillAttributeTypeL11nMapper;
 use Modules\Billing\Models\Attribute\BillAttributeTypeMapper;
-use Modules\Billing\Models\Attribute\BillAttributeValue;
 use Modules\Billing\Models\Attribute\BillAttributeValueL11nMapper;
 use Modules\Billing\Models\Attribute\BillAttributeValueMapper;
-use Modules\Billing\Models\Attribute\NullBillAttributeType;
-use Modules\Billing\Models\Attribute\NullBillAttributeValue;
 use phpOMS\Localization\BaseStringL11n;
 use phpOMS\Localization\ISO639x1Enum;
 use phpOMS\Message\Http\RequestStatusCode;
@@ -75,18 +75,18 @@ final class ApiAttributeController extends Controller
      *
      * @param RequestAbstract $request Request
      *
-     * @return BillAttribute
+     * @return Attribute
      *
      * @since 1.0.0
      */
-    private function createBillAttributeFromRequest(RequestAbstract $request) : BillAttribute
+    private function createBillAttributeFromRequest(RequestAbstract $request) : Attribute
     {
-        $attribute       = new BillAttribute();
-        $attribute->bill = (int) $request->getData('bill');
-        $attribute->type = new NullBillAttributeType((int) $request->getData('type'));
+        $attribute       = new Attribute();
+        $attribute->ref  = (int) $request->getData('ref');
+        $attribute->type = new NullAttributeType((int) $request->getData('type'));
 
         if ($request->hasData('value')) {
-            $attribute->value = new NullBillAttributeValue((int) $request->getData('value'));
+            $attribute->value = new NullAttributeValue((int) $request->getData('value'));
         } else {
             $newRequest = clone $request;
             $newRequest->setData('value', $request->getData('custom'), true);
@@ -223,13 +223,13 @@ final class ApiAttributeController extends Controller
      *
      * @param RequestAbstract $request Request
      *
-     * @return BillAttributeType
+     * @return AttributeType
      *
      * @since 1.0.0
      */
-    private function createBillAttributeTypeFromRequest(RequestAbstract $request) : BillAttributeType
+    private function createBillAttributeTypeFromRequest(RequestAbstract $request) : AttributeType
     {
-        $attrType                    = new BillAttributeType($request->getDataString('name') ?? '');
+        $attrType                    = new AttributeType($request->getDataString('name') ?? '');
         $attrType->datatype          = $request->getDataInt('datatype') ?? 0;
         $attrType->custom            = $request->getDataBool('custom') ?? false;
         $attrType->isRequired        = (bool) ($request->getData('is_required') ?? false);
@@ -303,20 +303,20 @@ final class ApiAttributeController extends Controller
      *
      * @param RequestAbstract $request Request
      *
-     * @return BillAttributeValue
+     * @return AttributeValue
      *
      * @since 1.0.0
      */
-    private function createBillAttributeValueFromRequest(RequestAbstract $request) : BillAttributeValue
+    private function createBillAttributeValueFromRequest(RequestAbstract $request) : AttributeValue
     {
-        /** @var BillAttributeType $type */
+        /** @var \Modules\Attribute\Models\AttributeType $type */
         $type = BillAttributeTypeMapper::get()
             ->where('id', $request->getDataInt('type') ?? 0)
             ->execute();
 
-        $attrValue            = new BillAttributeValue();
+        $attrValue            = new AttributeValue();
         $attrValue->isDefault = $request->getDataBool('default') ?? false;
-        $attrValue->setValue($request->getData('value'), $type->datatype);
+        $attrValue->setValue($request->getDataString('value'), $type->datatype);
 
         if ($request->hasData('title')) {
             $attrValue->setL11n($request->getDataString('title') ?? '', $request->getDataString('language') ?? ISO639x1Enum::_EN);
diff --git a/Controller/ApiBillController.php b/Controller/ApiBillController.php
index 6872e64..4f9c799 100755
--- a/Controller/ApiBillController.php
+++ b/Controller/ApiBillController.php
@@ -25,13 +25,9 @@ use Modules\Billing\Models\BillMapper;
 use Modules\Billing\Models\BillStatus;
 use Modules\Billing\Models\BillTypeMapper;
 use Modules\Billing\Models\SettingsEnum;
-use Modules\Billing\Models\Tax\TaxCombinationMapper;
 use Modules\ClientManagement\Models\Client;
 use Modules\ClientManagement\Models\ClientMapper;
-use Modules\Finance\Models\TaxCode;
-use Modules\Finance\Models\TaxCodeMapper;
 use Modules\ItemManagement\Models\Item;
-use Modules\ItemManagement\Models\ItemL11nMapper;
 use Modules\ItemManagement\Models\ItemMapper;
 use Modules\Media\Models\CollectionMapper;
 use Modules\Media\Models\MediaMapper;
@@ -44,7 +40,6 @@ use phpOMS\Autoloader;
 use phpOMS\Localization\ISO3166TwoEnum;
 use phpOMS\Localization\ISO4217CharEnum;
 use phpOMS\Localization\ISO639x1Enum;
-use phpOMS\Localization\Money;
 use phpOMS\Message\Http\RequestStatusCode;
 use phpOMS\Message\NotificationLevel;
 use phpOMS\Message\RequestAbstract;
@@ -181,8 +176,8 @@ final class ApiBillController extends Controller
     /**
      * Create a base Bill object with default values
      *
-     * @param Client           $client  The client object for whom the bill is being created
-     * @param RequestAbstract  $request The request object that contains the header account
+     * @param Client          $client  The client object for whom the bill is being created
+     * @param RequestAbstract $request The request object that contains the header account
      *
      * @return Bill                     The new Bill object with default values
      *
@@ -197,19 +192,20 @@ final class ApiBillController extends Controller
     public function createBaseBill(Client $client, RequestAbstract $request) : Bill
     {
         // @todo: validate vat before creation
-        $bill = new Bill();
+        $bill                  = new Bill();
+        $bill->createdBy       = new NullAccount($request->header->account);
+        $bill->billDate        = new \DateTime('now'); // @todo: Date of payment
+        $bill->performanceDate = new \DateTime('now'); // @todo: Date of payment
+        $bill->accountNumber   = $client->number;
         $bill->setStatus(BillStatus::DRAFT);
-        $bill->createdBy = new NullAccount($request->header->account);
-        $bill->billDate  = new \DateTime('now'); // @todo: Date of payment
-        $bill->performanceDate  = new \DateTime('now'); // @todo: Date of payment
-        $bill->accountNumber = $client->number;
 
-        $bill->shipping = 0;
+        $bill->shipping     = 0;
         $bill->shippingText = '';
 
-        $bill->payment = 0;
+        $bill->payment     = 0;
         $bill->paymentText = '';
 
+        /** @var \Modules\Billing\Modles\BillType */
         $bill->type = BillTypeMapper::get()
             ->where('name', 'sales_invoice')
             ->execute();
@@ -268,6 +264,18 @@ final class ApiBillController extends Controller
         return $bill;
     }
 
+    /**
+     * Create a base BillElement object with default values
+     *
+     * @param Client          $client  The client object for whom the bill is being created
+     * @param Item            $item    The item object for which the bill element is being created
+     * @param Bill            $bill    The bill object for which the bill element is being created
+     * @param RequestAbstract $request The request object that contains the header account
+     *
+     * @return BillElement
+     *
+     * @since 1.0.0
+     */
     public function createBaseBillElement(Client $client, Item $item, Bill $bill, RequestAbstract $request) : BillElement
     {
         $taxCode = $this->app->moduleManager->get('Billing', 'ApiTax')->getTaxCodeFromClientItem($client, $item, $request->getCountry());
@@ -317,26 +325,26 @@ final class ApiBillController extends Controller
             ->where('id', $request->getDataInt('type') ?? 1)
             ->execute();
 
-        /* @var \Modules\Account\Models\Account $account */
-        $bill               = new Bill();
-        $bill->createdBy    = new NullAccount($request->header->account);
-        $bill->type         = $billType;
         // @todo: use defaultInvoiceAddress or mainAddress. also consider to use billto1, billto2, billto3 (for multiple lines e.g. name2, fao etc.)
-        $bill->billTo          = (string) ($request->getDataString('billto')
+        /** @var \Modules\SupplierManagement\Models\Supplier|\Modules\ClientManagement\Models\Client $account */
+        $bill              = new Bill();
+        $bill->createdBy   = new NullAccount($request->header->account);
+        $bill->type        = $billType;
+        $bill->billTo      = (string) ($request->getDataString('billto')
             ?? ($account->account->name1 . (!empty($account->account->name2)
                 ? ', ' . $account->account->name2
                 : ''
             )));
-        $bill->billAddress     = (string) ($request->getDataString('billaddress') ?? $account->mainAddress->address);
-        $bill->billZip         = (string) ($request->getDataString('billtopostal') ?? $account->mainAddress->postal);
-        $bill->billCity        = (string) ($request->getDataString('billtocity') ?? $account->mainAddress->city);
-        $bill->billCountry     = (string) (
+        $bill->billAddress = (string) ($request->getDataString('billaddress') ?? $account->mainAddress->address);
+        $bill->billZip     = (string) ($request->getDataString('billtopostal') ?? $account->mainAddress->postal);
+        $bill->billCity    = (string) ($request->getDataString('billtocity') ?? $account->mainAddress->city);
+        $bill->billCountry = (string) (
             $request->getDataString('billtocountry') ?? (
                 ($country = $account->mainAddress->getCountry()) ===  ISO3166TwoEnum::_XXX ? '' : $country)
             );
         $bill->client          = !$request->hasData('client') ? null : $account;
         $bill->supplier        = !$request->hasData('supplier') ? null : $account;
-        $bill->performanceDate = new \DateTime($request->getDataString('performancedate') ?? 'now');
+        $bill->performanceDate = $request->getDataDateTime('performancedate') ?? new \DateTime('now');
         $bill->setStatus($request->getDataInt('status') ?? BillStatus::ACTIVE);
 
         return $bill;
@@ -560,6 +568,7 @@ final class ApiBillController extends Controller
      *
      * @param RequestAbstract  $request  Request
      * @param ResponseAbstract $response Response
+     * @param Bill             $bill     Bill to create element for
      * @param mixed            $data     Generic data
      *
      * @return BillElement
@@ -610,6 +619,19 @@ final class ApiBillController extends Controller
         return [];
     }
 
+    /**
+     * Api method  to create a bill preview
+     *
+     * @param RequestAbstract  $request  Request
+     * @param ResponseAbstract $response Response
+     * @param mixed            $data     Generic data
+     *
+     * @return void
+     *
+     * @api
+     *
+     * @since 1.0.0
+     */
     public function apiPreviewRender(RequestAbstract $request, ResponseAbstract $response, mixed $data = null) : void
     {
         /** @var \Modules\Billing\Models\Bill $bill */
diff --git a/Controller/ApiController.php b/Controller/ApiController.php
index 351877d..abd758a 100755
--- a/Controller/ApiController.php
+++ b/Controller/ApiController.php
@@ -101,6 +101,19 @@ final class ApiController extends Controller
         $this->app->moduleManager->get('Billing', 'ApiBill')->apiBillElementCreate($request, $response, $data);
     }
 
+    /**
+     * Api method to create a bill preview
+     *
+     * @param RequestAbstract  $request  Request
+     * @param ResponseAbstract $response Response
+     * @param mixed            $data     Generic data
+     *
+     * @return void
+     *
+     * @api
+     *
+     * @since 1.0.0
+     */
     public function apiPreviewRender(RequestAbstract $request, ResponseAbstract $response, mixed $data = null) : void
     {
         $this->app->moduleManager->get('Billing', 'ApiBill')->apiPreviewRender($request, $response, $data);
diff --git a/Controller/ApiPriceController.php b/Controller/ApiPriceController.php
index c881cdc..87b1193 100755
--- a/Controller/ApiPriceController.php
+++ b/Controller/ApiPriceController.php
@@ -16,16 +16,15 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Controller;
 
+use Modules\Attribute\Models\NullAttributeValue;
 use Modules\Billing\Models\Price\Price;
 use Modules\Billing\Models\Price\PriceMapper;
 use Modules\Billing\Models\Price\PriceType;
 use Modules\Billing\Models\Tax\TaxCombinationMapper;
 use Modules\ClientManagement\Models\ClientMapper;
 use Modules\ClientManagement\Models\NullClient;
-use Modules\ClientManagement\Models\NullClientAttributeValue;
 use Modules\ItemManagement\Models\ItemMapper;
 use Modules\ItemManagement\Models\NullItem;
-use Modules\ItemManagement\Models\NullItemAttributeValue;
 use Modules\SupplierManagement\Models\NullSupplier;
 use Modules\SupplierManagement\Models\SupplierMapper;
 use phpOMS\Localization\ISO4217CharEnum;
@@ -209,11 +208,11 @@ final class ApiPriceController extends Controller
         $tax = ($request->getDataInt('price_type') ?? PriceType::SALES) === PriceType::SALES
             ? TaxCombinationMapper::get()
                 ->where('itemCode', $request->getDataInt('price_item'))
-                ->where('clientCode', $account->getAttribute('client_code')->getId())
+                ->where('clientCode', $account->getAttribute('client_code')?->value->getId())
                 ->execute()
             : TaxCombinationMapper::get()
                 ->where('itemCode', $request->getDataInt('price_item'))
-                ->where('supplierCode', $account->getAttribute('supplier_code')->getId())
+                ->where('supplierCode', $account->getAttribute('supplier_code')?->value->getId())
                 ->execute();
 
         $response->header->set('Content-Type', MimeType::M_JSON, true);
@@ -267,16 +266,16 @@ final class ApiPriceController extends Controller
         $price->promocode = $request->getDataString('promocode') ?? '';
 
         $price->item        = new NullItem((int) $request->getData('item'));
-        $price->itemgroup   = new NullItemAttributeValue((int) $request->getData('itemgroup'));
-        $price->itemsegment = new NullItemAttributeValue((int) $request->getData('itemsegment'));
-        $price->itemsection = new NullItemAttributeValue((int) $request->getData('itemsection'));
-        $price->itemtype    = new NullItemAttributeValue((int) $request->getData('itemtype'));
+        $price->itemgroup   = new NullAttributeValue((int) $request->getData('itemgroup'));
+        $price->itemsegment = new NullAttributeValue((int) $request->getData('itemsegment'));
+        $price->itemsection = new NullAttributeValue((int) $request->getData('itemsection'));
+        $price->itemtype    = new NullAttributeValue((int) $request->getData('itemtype'));
 
         $price->client        = new NullClient((int) $request->getData('client'));
-        $price->clientgroup   = new NullClientAttributeValue((int) $request->getData('clientgroup'));
-        $price->clientsegment = new NullClientAttributeValue((int) $request->getData('clientsegment'));
-        $price->clientsection = new NullClientAttributeValue((int) $request->getData('clientsection'));
-        $price->clienttype    = new NullClientAttributeValue((int) $request->getData('clienttype'));
+        $price->clientgroup   = new NullAttributeValue((int) $request->getData('clientgroup'));
+        $price->clientsegment = new NullAttributeValue((int) $request->getData('clientsegment'));
+        $price->clientsection = new NullAttributeValue((int) $request->getData('clientsection'));
+        $price->clienttype    = new NullAttributeValue((int) $request->getData('clienttype'));
 
         $price->supplier           = new NullSupplier((int) $request->getData('supplier'));
         $price->unit               = (int) $request->getData('unit');
@@ -289,8 +288,8 @@ final class ApiPriceController extends Controller
         $price->bonus              = (int) $request->getData('bonus');
         $price->multiply           = $request->getDataBool('multiply') ?? false;
         $price->currency           = $request->getDataString('currency') ?? ISO4217CharEnum::_EUR;
-        $price->start              = $request->hasData('start') ? new \DateTime($request->getDataString('start')) : null;
-        $price->end                = $request->hasData('end') ? new \DateTime($request->getDataString('end')) : null;
+        $price->start              = $request->getDataDateTime('start') ?? null;
+        $price->end                = $request->getDataDateTime('end') ?? null;
 
         return $price;
     }
diff --git a/Controller/ApiTaxController.php b/Controller/ApiTaxController.php
index de00f16..d029c2a 100755
--- a/Controller/ApiTaxController.php
+++ b/Controller/ApiTaxController.php
@@ -17,19 +17,17 @@ declare(strict_types=1);
 namespace Modules\Billing\Controller;
 
 use Modules\Admin\Models\Address;
+use Modules\Attribute\Models\AttributeValue;
+use Modules\Attribute\Models\NullAttributeValue;
 use Modules\Billing\Models\Tax\TaxCombination;
 use Modules\Billing\Models\Tax\TaxCombinationMapper;
 use Modules\ClientManagement\Models\Client;
 use Modules\ClientManagement\Models\ClientAttributeTypeMapper;
-use Modules\ClientManagement\Models\ClientAttributeValue;
-use Modules\ClientManagement\Models\NullClientAttributeValue;
 use Modules\Finance\Models\NullTaxCode;
 use Modules\Finance\Models\TaxCode;
 use Modules\Finance\Models\TaxCodeMapper;
 use Modules\ItemManagement\Models\Item;
-use Modules\ItemManagement\Models\NullItemAttributeValue;
 use Modules\Organization\Models\UnitMapper;
-use Modules\SupplierManagement\Models\NullSupplierAttributeValue;
 use phpOMS\Localization\ISO3166CharEnum;
 use phpOMS\Message\Http\RequestStatusCode;
 use phpOMS\Message\NotificationLevel;
@@ -47,6 +45,17 @@ use phpOMS\Model\Message\FormValidation;
  */
 final class ApiTaxController extends Controller
 {
+    /**
+     * Get tax code from client and item.
+     *
+     * @param Client $client         Client to get tax code from
+     * @param Item   $item           Item toget tax code from
+     * @param string $defaultCountry Default country to use if no valid tax code could be found and if the unit country code shouldn't be used.
+     *
+     * @return TaxCode
+     *
+     * @since 1.0.0
+     */
     public function getTaxCodeFromClientItem(Client $client, Item $item, string $defaultCountry = '') : TaxCode
     {
         // @todo: define default sales tax code if none available?!
@@ -71,7 +80,7 @@ final class ApiTaxController extends Controller
                 ->execute();
 
             // Create dummy client
-            $client = new Client();
+            $client              = new Client();
             $client->mainAddress =  $unit->mainAddress;
 
             if (!empty($defaultCountry)) {
@@ -81,7 +90,6 @@ final class ApiTaxController extends Controller
             $taxCodeAttribute = $this->getClientTaxCode($client,  $unit->mainAddress);
 
             /** @var \Modules\Billing\Models\Tax\TaxCombination $taxCombination */
-            $t = $item->getAttribute('sales_tax_code');
             $taxCombination = TaxCombinationMapper::get()
                 ->where('itemCode', $item->getAttribute('sales_tax_code')?->value->getId())
                 ->where('clientCode', $taxCodeAttribute->getId())
@@ -96,6 +104,17 @@ final class ApiTaxController extends Controller
         return $taxCode;
     }
 
+    /**
+     * Create a tax combination for a client and item
+     *
+     * @param RequestAbstract  $request  Request
+     * @param ResponseAbstract $response Response
+     * @param mixed            $data     Data
+     *
+     * @return void
+     *
+     * @since 1.0.0
+     */
     public function apiTaxCombinationCreate(RequestAbstract $request, ResponseAbstract $response, mixed $data = null) : void
     {
         if (!empty($val = $this->validateTaxCombinationCreate($request))) {
@@ -125,12 +144,12 @@ final class ApiTaxController extends Controller
         $tax           = new TaxCombination();
         $tax->taxType  = $request->getDataInt('tax_type') ?? 1;
         $tax->taxCode  = (string) $request->getData('tax_code');
-        $tax->itemCode = new NullItemAttributeValue((int) $request->getData('item_code'));
+        $tax->itemCode = new NullAttributeValue((int) $request->getData('item_code'));
 
         if ($tax->taxType === 1) {
-            $tax->clientCode = new NullClientAttributeValue((int) $request->getData('account_code'));
+            $tax->clientCode = new NullAttributeValue((int) $request->getData('account_code'));
         } else {
-            $tax->supplierCode = new NullSupplierAttributeValue((int) $request->getData('account_code'));
+            $tax->supplierCode = new NullAttributeValue((int) $request->getData('account_code'));
         }
 
         return $tax;
@@ -165,19 +184,19 @@ final class ApiTaxController extends Controller
      * @param Client  $client           The client to get the tax code for
      * @param Address $taxOfficeAddress The tax office address used to determine the tax code
      *
-     * @return ClientAttributeValue   The client's tax code
+     * @return AttributeValue   The client's tax code
      *
      * @since 1.0.0
      */
-    public function getClientTaxCode(Client $client, Address $taxOfficeAddress) : ClientAttributeValue
+    public function getClientTaxCode(Client $client, Address $taxOfficeAddress) : AttributeValue
     {
-        /** @var \Modules\ClientManagement\Models\ClientAttributeType $codes */
+        /** @var \Modules\Attribute\Models\AttributeType $codes */
         $codes = ClientAttributeTypeMapper::get()
             ->with('defaults')
             ->where('name', 'sales_tax_code')
             ->execute();
 
-        $taxCode = new NullClientAttributeValue();
+        $taxCode = new NullAttributeValue();
 
         if ($taxOfficeAddress->getCountry() === $client->mainAddress->getCountry()) {
             $taxCode = $codes->getDefaultByValue($client->mainAddress->getCountry());
diff --git a/Controller/CliController.php b/Controller/CliController.php
index 87c2b28..881ed0e 100755
--- a/Controller/CliController.php
+++ b/Controller/CliController.php
@@ -81,6 +81,7 @@ final class CliController extends Controller
             $identifierContent = '{}';
         }
 
+        /** @var array $identifiers */
         $identifiers = \json_decode($identifierContent, true);
 
         /* Supplier */
@@ -341,8 +342,6 @@ final class CliController extends Controller
      *
      * @return int
      *
-     * @todo: This can be optimized by a lot!!!
-     *
      * @since 1.0.0
      */
     private function matchSupplier(string $content, array $suppliers) : int
@@ -352,8 +351,8 @@ final class CliController extends Controller
         // bill_match_pattern
         foreach ($suppliers as $supplier) {
             // @todo: consider to support regex?
-            if ((!empty($supplier->getAttributeByTypeName('bill_match_pattern')->value->valueStr)
-                    && \stripos($content, $supplier->getAttributeByTypeName('bill_match_pattern')->value->valueStr) !== false)
+            if ((!empty($supplier->getAttribute('bill_match_pattern')->value->valueStr)
+                    && \stripos($content, $supplier->getAttribute('bill_match_pattern')->value->valueStr) !== false)
             ) {
                 return $supplier->getId();
             }
@@ -407,9 +406,9 @@ final class CliController extends Controller
      */
     private function parseDate(string $date, Supplier $supplier, array $formats) : ?\DateTime
     {
-        if ((!empty($supplier->getAttributeByTypeName('bill_date_format')->value->valueStr))) {
+        if ((!empty($supplier->getAttribute('bill_date_format')->value->valueStr))) {
             return \DateTime::createFromFormat(
-                $supplier->getAttributeByTypeName('bill_date_format')->value->valueStr,
+                $supplier->getAttribute('bill_date_format')?->value->valueStr ?? '',
                 $date
             );
         }
diff --git a/Models/Attribute/AttributeValueType.php b/Models/Attribute/AttributeValueType.php
deleted file mode 100755
index b6b4780..0000000
--- a/Models/Attribute/AttributeValueType.php
+++ /dev/null
@@ -1,40 +0,0 @@
-<?php
-/**
- * Karaka
- *
- * PHP Version 8.1
- *
- * @package   Modules\Billing\Models\Attribute
- * @copyright Dennis Eichhorn
- * @license   OMS License 2.0
- * @version   1.0.0
- * @link      https://jingga.app
- */
-declare(strict_types=1);
-
-namespace Modules\Billing\Models\Attribute;
-
-use phpOMS\Stdlib\Base\Enum;
-
-/**
- * Attribute value type enum.
- *
- * @package Modules\Billing\Models\Attribute
- * @license OMS License 2.0
- * @link    https://jingga.app
- * @since   1.0.0
- */
-abstract class AttributeValueType extends Enum
-{
-    public const _INT = 1;
-
-    public const _STRING = 2;
-
-    public const _FLOAT = 3;
-
-    public const _DATETIME = 4;
-
-    public const _BOOL = 5;
-
-    public const _FLOAT_INT = 6;
-}
diff --git a/Models/Attribute/BillAttribute.php b/Models/Attribute/BillAttribute.php
deleted file mode 100755
index e2c01c3..0000000
--- a/Models/Attribute/BillAttribute.php
+++ /dev/null
@@ -1,102 +0,0 @@
-<?php
-/**
- * Karaka
- *
- * PHP Version 8.1
- *
- * @package   Modules\Billing\Models\Attribute
- * @copyright Dennis Eichhorn
- * @license   OMS License 2.0
- * @version   1.0.0
- * @link      https://jingga.app
- */
-declare(strict_types=1);
-
-namespace Modules\Billing\Models\Attribute;
-
-/**
- * Bill class.
- *
- * @package Modules\Billing\Models\Attribute
- * @license OMS License 2.0
- * @link    https://jingga.app
- * @since   1.0.0
- */
-class BillAttribute implements \JsonSerializable
-{
-    /**
-     * Id.
-     *
-     * @var int
-     * @since 1.0.0
-     */
-    protected int $id = 0;
-
-    /**
-     * Bill this attribute belongs to
-     *
-     * @var int
-     * @since 1.0.0
-     */
-    public int $bill = 0;
-
-    /**
-     * Attribute type the attribute belongs to
-     *
-     * @var BillAttributeType
-     * @since 1.0.0
-     */
-    public BillAttributeType $type;
-
-    /**
-     * Attribute value the attribute belongs to
-     *
-     * @var BillAttributeValue
-     * @since 1.0.0
-     */
-    public BillAttributeValue $value;
-
-    /**
-     * Constructor.
-     *
-     * @since 1.0.0
-     */
-    public function __construct()
-    {
-        $this->type  = new NullBillAttributeType();
-        $this->value = new NullBillAttributeValue();
-    }
-
-    /**
-     * Get id
-     *
-     * @return int
-     *
-     * @since 1.0.0
-     */
-    public function getId() : int
-    {
-        return $this->id;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function toArray() : array
-    {
-        return [
-            'id'    => $this->id,
-            'bill'  => $this->bill,
-            'type'  => $this->type,
-            'value' => $this->value,
-        ];
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function jsonSerialize() : mixed
-    {
-        return $this->toArray();
-    }
-}
diff --git a/Models/Attribute/BillAttributeMapper.php b/Models/Attribute/BillAttributeMapper.php
index 5b34b5f..09fd5c4 100755
--- a/Models/Attribute/BillAttributeMapper.php
+++ b/Models/Attribute/BillAttributeMapper.php
@@ -14,6 +14,7 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Models\Attribute;
 
+use Modules\Attribute\Models\Attribute;
 use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
 
 /**
@@ -34,7 +35,7 @@ final class BillAttributeMapper extends DataMapperFactory
      */
     public const COLUMNS = [
         'billing_bill_attr_id'    => ['name' => 'billing_bill_attr_id',    'type' => 'int', 'internal' => 'id'],
-        'billing_bill_attr_bill'  => ['name' => 'billing_bill_attr_bill',  'type' => 'int', 'internal' => 'bill'],
+        'billing_bill_attr_bill'  => ['name' => 'billing_bill_attr_bill',  'type' => 'int', 'internal' => 'ref'],
         'billing_bill_attr_type'  => ['name' => 'billing_bill_attr_type',  'type' => 'int', 'internal' => 'type'],
         'billing_bill_attr_value' => ['name' => 'billing_bill_attr_value', 'type' => 'int', 'internal' => 'value'],
     ];
@@ -56,6 +57,14 @@ final class BillAttributeMapper extends DataMapperFactory
         ],
     ];
 
+    /**
+     * Model to use by the mapper.
+     *
+     * @var class-string
+     * @since 1.0.0
+     */
+    public const MODEL = Attribute::class;
+
     /**
      * Primary table.
      *
diff --git a/Models/Attribute/BillAttributeType.php b/Models/Attribute/BillAttributeType.php
deleted file mode 100755
index e09757e..0000000
--- a/Models/Attribute/BillAttributeType.php
+++ /dev/null
@@ -1,216 +0,0 @@
-<?php
-/**
- * Karaka
- *
- * PHP Version 8.1
- *
- * @package   Modules\Billing\Models\Attribute
- * @copyright Dennis Eichhorn
- * @license   OMS License 2.0
- * @version   1.0.0
- * @link      https://jingga.app
- */
-declare(strict_types=1);
-
-namespace Modules\Billing\Models\Attribute;
-
-use phpOMS\Localization\BaseStringL11n;
-use phpOMS\Localization\ISO639x1Enum;
-
-/**
- * Bill Attribute Type class.
- *
- * @package Modules\Billing\Models\Attribute
- * @license OMS License 2.0
- * @link    https://jingga.app
- * @since   1.0.0
- */
-class BillAttributeType implements \JsonSerializable
-{
-    /**
-     * Id
-     *
-     * @var int
-     * @since 1.0.0
-     */
-    protected int $id = 0;
-
-    /**
-     * Name/string identifier by which it can be found/categorized
-     *
-     * @var string
-     * @since 1.0.0
-     */
-    public string $name = '';
-
-    /**
-     * Which field data type is required (string, int, ...) in the value
-     *
-     * @var int
-     * @since 1.0.0
-     */
-    protected int $fields = 0;
-
-    /**
-     * Is a custom value allowed (e.g. custom string)
-     *
-     * @var bool
-     * @since 1.0.0
-     */
-    public bool $custom = false;
-
-    public string $validationPattern = '';
-
-    public bool $isRequired = false;
-
-    /**
-     * Datatype of the attribute
-     *
-     * @var int
-     * @since 1.0.0
-     */
-    public int $datatype = AttributeValueType::_STRING;
-
-    /**
-     * Localization
-     *
-     * @var BaseStringL11n
-     */
-    private string | BaseStringL11n $l11n = '';
-
-    /**
-     * Possible default attribute values
-     *
-     * @var array
-     */
-    private array $defaults = [];
-
-    /**
-     * Default attribute value
-     *
-     * @var int
-     * @since 1.0.0
-     */
-    public int $default = 0;
-
-    /**
-     * Constructor.
-     *
-     * @param string $name Name/identifier of the attribute type
-     *
-     * @since 1.0.0
-     */
-    public function __construct(string $name = '')
-    {
-        $this->name = $name;
-    }
-
-    /**
-     * Get id
-     *
-     * @return int
-     *
-     * @since 1.0.0
-     */
-    public function getId() : int
-    {
-        return $this->id;
-    }
-
-    public function getDefaultByValue(mixed $value) : BillAttributeValue
-    {
-        foreach ($this->defaults as $default) {
-            if ($default->getValue() === $value) {
-                return $default;
-            }
-        }
-
-        return new NullBillAttributeValue();
-    }
-
-    /**
-     * Set l11n
-     *
-     * @param string|BaseStringL11n $l11n Tag article l11n
-     * @param string                $lang Language
-     *
-     * @return void
-     *
-     * @since 1.0.0
-     */
-    public function setL11n(string | BaseStringL11n $l11n, string $lang = ISO639x1Enum::_EN) : void
-    {
-        if ($l11n instanceof BaseStringL11n) {
-            $this->l11n = $l11n;
-        } elseif (isset($this->l11n) && $this->l11n instanceof BaseStringL11n) {
-            $this->l11n->content = $l11n;
-            $this->l11n->setLanguage($lang);
-        } else {
-            $this->l11n          = new BaseStringL11n();
-            $this->l11n->content = $l11n;
-            $this->l11n->setLanguage($lang);
-        }
-    }
-
-    /**
-     * @return string
-     *
-     * @since 1.0.0
-     */
-    public function getL11n() : string
-    {
-        if (!isset($this->l11n)) {
-            return '';
-        }
-
-        return $this->l11n instanceof BaseStringL11n ? $this->l11n->content : $this->l11n;
-    }
-
-    /**
-     * Set fields
-     *
-     * @param int $fields Fields
-     *
-     * @return void
-     *
-     * @since 1.0.0
-     */
-    public function setFields(int $fields) : void
-    {
-        $this->fields = $fields;
-    }
-
-    /**
-     * Get default values
-     *
-     * @return array
-     *
-     * @sicne 1.0.0
-     */
-    public function getDefaults() : array
-    {
-        return $this->defaults;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function toArray() : array
-    {
-        return [
-            'id'                => $this->id,
-            'name'              => $this->name,
-            'validationPattern' => $this->validationPattern,
-            'custom'            => $this->custom,
-            'isRequired'        => $this->isRequired,
-        ];
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function jsonSerialize() : mixed
-    {
-        return $this->toArray();
-    }
-}
diff --git a/Models/Attribute/BillAttributeTypeMapper.php b/Models/Attribute/BillAttributeTypeMapper.php
index ac44163..64761ed 100755
--- a/Models/Attribute/BillAttributeTypeMapper.php
+++ b/Models/Attribute/BillAttributeTypeMapper.php
@@ -14,6 +14,7 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Models\Attribute;
 
+use Modules\Attribute\Models\AttributeType;
 use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
 
 /**
@@ -64,6 +65,14 @@ final class BillAttributeTypeMapper extends DataMapperFactory
         ],
     ];
 
+    /**
+     * Model to use by the mapper.
+     *
+     * @var class-string
+     * @since 1.0.0
+     */
+    public const MODEL = AttributeType::class;
+
     /**
      * Primary table.
      *
diff --git a/Models/Attribute/BillAttributeValue.php b/Models/Attribute/BillAttributeValue.php
deleted file mode 100755
index aa3855e..0000000
--- a/Models/Attribute/BillAttributeValue.php
+++ /dev/null
@@ -1,230 +0,0 @@
-<?php
-/**
- * Karaka
- *
- * PHP Version 8.1
- *
- * @package   Modules\Billing\Models\Attribute
- * @copyright Dennis Eichhorn
- * @license   OMS License 2.0
- * @version   1.0.0
- * @link      https://jingga.app
- */
-declare(strict_types=1);
-
-namespace Modules\Billing\Models\Attribute;
-
-use phpOMS\Localization\BaseStringL11n;
-use phpOMS\Localization\ISO639x1Enum;
-
-/**
- * Bill attribute value class.
- *
- * The relation with the type/bill is defined in the BillAttribute class.
- *
- * @package Modules\Billing\Models\Attribute
- * @license OMS License 2.0
- * @link    https://jingga.app
- * @since   1.0.0
- */
-class BillAttributeValue implements \JsonSerializable
-{
-    /**
-     * Id
-     *
-     * @var int
-     * @since 1.0.0
-     */
-    protected int $id = 0;
-
-    /**
-     * Depending attribute type
-     *
-     * @var null|int
-     * @since 1.0.0
-     */
-    public ?int $dependingAttributeType = null;
-
-    /**
-     * Depending attribute value
-     *
-     * @var null|int
-     * @since 1.0.0
-     */
-    public ?int $dependingAttributeValue = null;
-
-    /**
-     * Int value
-     *
-     * @var null|int
-     * @since 1.0.0
-     */
-    public ?int $valueInt = null;
-
-    /**
-     * String value
-     *
-     * @var null|string
-     * @since 1.0.0
-     */
-    public ?string $valueStr = null;
-
-    /**
-     * Decimal value
-     *
-     * @var null|float
-     * @since 1.0.0
-     */
-    public ?float $valueDec = null;
-
-    /**
-     * DateTime value
-     *
-     * @var null|\DateTimeInterface
-     * @since 1.0.0
-     */
-    public ?\DateTimeInterface $valueDat = null;
-
-    /**
-     * Is a default value which can be selected
-     *
-     * @var bool
-     * @since 1.0.0
-     */
-    public bool $isDefault = false;
-
-    /**
-     * Unit of the value
-     *
-     * @var string
-     * @since 1.0.0
-     */
-    public string $unit = '';
-
-    /**
-     * Localization
-     *
-     * @var null|BaseStringL11n
-     */
-    private ?BaseStringL11n $l11n = null;
-
-    /**
-     * Get id
-     *
-     * @return int
-     *
-     * @since 1.0.0
-     */
-    public function getId() : int
-    {
-        return $this->id;
-    }
-
-    /**
-     * Set l11n
-     *
-     * @param string|BaseStringL11n $l11n Tag article l11n
-     * @param string                $lang Language
-     *
-     * @return void
-     *
-     * @since 1.0.0
-     */
-    public function setL11n(string | BaseStringL11n $l11n, string $lang = ISO639x1Enum::_EN) : void
-    {
-        if ($l11n instanceof BaseStringL11n) {
-            $this->l11n = $l11n;
-        } elseif (isset($this->l11n) && $this->l11n instanceof BaseStringL11n) {
-            $this->l11n->content = $l11n;
-            $this->l11n->setLanguage($lang);
-        } else {
-            $this->l11n          = new BaseStringL11n();
-            $this->l11n->content = $l11n;
-            $this->l11n->ref     = $this->id;
-            $this->l11n->setLanguage($lang);
-        }
-    }
-
-    /**
-     * Get localization
-     *
-     * @return null|string
-     *
-     * @since 1.0.0
-     */
-    public function getL11n() : ?string
-    {
-        return $this->l11n instanceof BaseStringL11n ? $this->l11n->content : $this->l11n;
-    }
-
-    /**
-     * Set value
-     *
-     * @param int|string|float $value    Value
-     * @param int              $datatype Datatype
-     *
-     * @return void
-     *
-     * @since 1.0.0
-     */
-    public function setValue(mixed $value, int $datatype) : void
-    {
-        if ($datatype === AttributeValueType::_STRING) {
-            $this->valueStr = (string) $value;
-        } elseif ($datatype === AttributeValueType::_INT
-            || $datatype === AttributeValueType::_FLOAT_INT
-            || $datatype === AttributeValueType::_BOOL
-        ) {
-            $this->valueInt = (int) $value;
-        } elseif ($datatype === AttributeValueType::_FLOAT) {
-            $this->valueDec = (float) $value;
-        } elseif ($datatype === AttributeValueType::_DATETIME) {
-            $this->valueDat = new \DateTime((string) $value);
-        }
-    }
-
-    /**
-     * Get value
-     *
-     * @return null|int|string|float|\DateTimeInterface
-     *
-     * @since 1.0.0
-     */
-    public function getValue() : mixed
-    {
-        if (!empty($this->valueStr)) {
-            return $this->valueStr;
-        } elseif (!empty($this->valueInt)) {
-            return $this->valueInt;
-        } elseif (!empty($this->valueDec)) {
-            return $this->valueDec;
-        } elseif ($this->valueDat instanceof \DateTimeInterface) {
-            return $this->valueDat;
-        }
-
-        return null;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function toArray() : array
-    {
-        return [
-            'id'        => $this->id,
-            'valueInt'  => $this->valueInt,
-            'valueStr'  => $this->valueStr,
-            'valueDec'  => $this->valueDec,
-            'valueDat'  => $this->valueDat,
-            'isDefault' => $this->isDefault,
-        ];
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function jsonSerialize() : mixed
-    {
-        return $this->toArray();
-    }
-}
diff --git a/Models/Attribute/BillAttributeValueMapper.php b/Models/Attribute/BillAttributeValueMapper.php
index 92e8090..1fe664e 100755
--- a/Models/Attribute/BillAttributeValueMapper.php
+++ b/Models/Attribute/BillAttributeValueMapper.php
@@ -14,6 +14,7 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Models\Attribute;
 
+use Modules\Attribute\Models\AttributeValue;
 use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
 
 /**
@@ -59,6 +60,14 @@ final class BillAttributeValueMapper extends DataMapperFactory
         ],
     ];
 
+    /**
+     * Model to use by the mapper.
+     *
+     * @var class-string
+     * @since 1.0.0
+     */
+    public const MODEL = AttributeValue::class;
+
     /**
      * Primary table.
      *
diff --git a/Models/Attribute/NullBillAttribute.php b/Models/Attribute/NullBillAttribute.php
deleted file mode 100755
index 2f2a716..0000000
--- a/Models/Attribute/NullBillAttribute.php
+++ /dev/null
@@ -1,47 +0,0 @@
-<?php
-/**
- * Karaka
- *
- * PHP Version 8.1
- *
- * @package   Modules\Billing\Models\Attribute
- * @copyright Dennis Eichhorn
- * @license   OMS License 2.0
- * @version   1.0.0
- * @link      https://jingga.app
- */
-declare(strict_types=1);
-
-namespace Modules\Billing\Models\Attribute;
-
-/**
- * Null model
- *
- * @package Modules\Billing\Models\Attribute
- * @license OMS License 2.0
- * @link    https://jingga.app
- * @since   1.0.0
- */
-final class NullBillAttribute extends BillAttribute
-{
-    /**
-     * Constructor
-     *
-     * @param int $id Model id
-     *
-     * @since 1.0.0
-     */
-    public function __construct(int $id = 0)
-    {
-        parent::__construct();
-        $this->id = $id;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function jsonSerialize() : mixed
-    {
-        return ['id' => $this->id];
-    }
-}
diff --git a/Models/Attribute/NullBillAttributeType.php b/Models/Attribute/NullBillAttributeType.php
deleted file mode 100755
index 04e178c..0000000
--- a/Models/Attribute/NullBillAttributeType.php
+++ /dev/null
@@ -1,46 +0,0 @@
-<?php
-/**
- * Karaka
- *
- * PHP Version 8.1
- *
- * @package   Modules\Billing\Models\Attribute
- * @copyright Dennis Eichhorn
- * @license   OMS License 2.0
- * @version   1.0.0
- * @link      https://jingga.app
- */
-declare(strict_types=1);
-
-namespace Modules\Billing\Models\Attribute;
-
-/**
- * Null model
- *
- * @package Modules\Billing\Models\Attribute
- * @license OMS License 2.0
- * @link    https://jingga.app
- * @since   1.0.0
- */
-final class NullBillAttributeType extends BillAttributeType
-{
-    /**
-     * Constructor
-     *
-     * @param int $id Model id
-     *
-     * @since 1.0.0
-     */
-    public function __construct(int $id = 0)
-    {
-        $this->id = $id;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function jsonSerialize() : mixed
-    {
-        return ['id' => $this->id];
-    }
-}
diff --git a/Models/Attribute/NullBillAttributeValue.php b/Models/Attribute/NullBillAttributeValue.php
deleted file mode 100755
index 4f9f338..0000000
--- a/Models/Attribute/NullBillAttributeValue.php
+++ /dev/null
@@ -1,46 +0,0 @@
-<?php
-/**
- * Karaka
- *
- * PHP Version 8.1
- *
- * @package   Modules\Billing\Models\Attribute
- * @copyright Dennis Eichhorn
- * @license   OMS License 2.0
- * @version   1.0.0
- * @link      https://jingga.app
- */
-declare(strict_types=1);
-
-namespace Modules\Billing\Models\Attribute;
-
-/**
- * Null model
- *
- * @package Modules\Billing\Models\Attribute
- * @license OMS License 2.0
- * @link    https://jingga.app
- * @since   1.0.0
- */
-final class NullBillAttributeValue extends BillAttributeValue
-{
-    /**
-     * Constructor
-     *
-     * @param int $id Model id
-     *
-     * @since 1.0.0
-     */
-    public function __construct(int $id = 0)
-    {
-        $this->id = $id;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function jsonSerialize() : mixed
-    {
-        return ['id' => $this->id];
-    }
-}
diff --git a/Models/Bill.php b/Models/Bill.php
index 3fdb03d..77fd1c8 100755
--- a/Models/Bill.php
+++ b/Models/Bill.php
@@ -442,7 +442,7 @@ class Bill implements \JsonSerializable
     /**
      * Attributes.
      *
-     * @var BillAttribute[]
+     * @var \Modules\Attribute\Models\Attribute[]
      * @since 1.0.0
      */
     private array $attributes = [];
@@ -525,52 +525,6 @@ class Bill implements \JsonSerializable
         return $this->number;
     }
 
-    /**
-     * Add attribute to client
-     *
-     * @param BillAttribute $attribute Attribute
-     *
-     * @return void
-     *
-     * @since 1.0.0
-     */
-    public function addAttribute(BillAttribute $attribute) : void
-    {
-        $this->attributes[] = $attribute;
-    }
-
-    /**
-     * Get attributes
-     *
-     * @return BillAttribute[]
-     *
-     * @since 1.0.0
-     */
-    public function getAttributes() : array
-    {
-        return $this->attributes;
-    }
-
-    /**
-     * Get attribute
-     *
-     * @param string $attrName Attribute name
-     *
-     * @return null|BillAttribute
-     *
-     * @since 1.0.0
-     */
-    public function getAttribute(string $attrName) : ?BillAttribute
-    {
-        foreach ($this->attributes as $attribute) {
-            if ($attribute->type->name === $attrName) {
-                return $attribute;
-            }
-        }
-
-        return null;
-    }
-
     /**
      * Get status
      *
@@ -892,4 +846,6 @@ class Bill implements \JsonSerializable
     {
         return $this->toArray();
     }
+
+    use \Modules\Attribute\Models\AttributeHolderTrait;
 }
diff --git a/Models/BillElement.php b/Models/BillElement.php
index 8e215fc..792db58 100755
--- a/Models/BillElement.php
+++ b/Models/BillElement.php
@@ -101,7 +101,7 @@ class BillElement implements \JsonSerializable
     /**
      * Tax percentage
      *
-     * @var null|FloatInt
+     * @var FloatInt
      * @since 1.0.0
      */
     public FloatInt $taxR;
@@ -176,6 +176,15 @@ class BillElement implements \JsonSerializable
         return $this->id;
     }
 
+    /**
+     * Set the element quantity.
+     *
+     * @param int $quantity Quantity
+     *
+     * @return void
+     *
+     * @since 1.0.0
+     */
     public function setQuantity(int $quantity) : void
     {
         if ($this->quantity === $quantity) {
@@ -186,6 +195,13 @@ class BillElement implements \JsonSerializable
         // @todo: recalculate all the prices!!!
     }
 
+    /**
+     * Get quantity.
+     *
+     * @return int
+     *
+     * @since 1.0.0
+     */
     public function getQuantity() : int
     {
         return $this->quantity;
@@ -205,14 +221,25 @@ class BillElement implements \JsonSerializable
         $this->item = $item;
     }
 
+    /**
+     * Create element from item
+     *
+     * @param Item    $item     Item
+     * @param TaxCode $code     Tax code used for gross amount calculation
+     * @param int     $quantity Quantity
+     *
+     * @return self
+     *
+     * @since 1.0.0
+     */
     public static function fromItem(Item $item, TaxCode $code, int $quantity = 1) : self
     {
-        $element = new self();
-        $element->item = $item->getId();
-        $element->itemNumber = $item->number;
-        $element->itemName = $item->getL11n('name1')->description;
+        $element                  = new self();
+        $element->item            = $item->getId();
+        $element->itemNumber      = $item->number;
+        $element->itemName        = $item->getL11n('name1')->description;
         $element->itemDescription = $item->getL11n('description_short')->description;
-        $element->quantity = $quantity;
+        $element->quantity        = $quantity;
 
         // @todo: Use pricing instead of the default sales price
         // @todo: discounts might be in quantities
@@ -226,7 +253,7 @@ class BillElement implements \JsonSerializable
         $element->singleProfitNet->setInt($element->singleSalesPriceNet->getInt() - $element->singlePurchasePriceNet->getInt());
         $element->totalProfitNet->setInt($element->quantity * ($element->totalSalesPriceNet->getInt() - $element->totalPurchasePriceNet->getInt()));
 
-        $element->taxP    = new FloatInt((int) (($code->percentageInvoice * $element->totalSalesPriceNet->getInt()) / 10000));
+        $element->taxP    = new Money((int) (($code->percentageInvoice * $element->totalSalesPriceNet->getInt()) / 10000));
         $element->taxR    = new FloatInt($code->percentageInvoice);
         $element->taxCode = $code->abbr;
 
diff --git a/Models/BillType.php b/Models/BillType.php
index b127d86..6c91103 100755
--- a/Models/BillType.php
+++ b/Models/BillType.php
@@ -66,7 +66,7 @@ class BillType implements \JsonSerializable
      */
     public function __construct(string $name = '')
     {
-        $this->name     = $name;
+        $this->name = $name;
     }
 
     /**
@@ -96,7 +96,7 @@ class BillType implements \JsonSerializable
         if ($l11n instanceof BaseStringL11n) {
             $this->l11n = $l11n;
         } elseif (isset($this->l11n) && $this->l11n instanceof BaseStringL11n) {
-            $this->l11n->content  = $l11n;
+            $this->l11n->content = $l11n;
             $this->l11n->setLanguage($lang);
         } else {
             $this->l11n          = new BaseStringL11n();
@@ -120,11 +120,27 @@ class BillType implements \JsonSerializable
         return $this->l11n instanceof BaseStringL11n ? $this->l11n->content : $this->l11n;
     }
 
+    /**
+     * Add rendering template
+     *
+     * @param Collection $template Template
+     *
+     * @return void
+     *
+     * @since 1.0.0
+     */
     public function addTemplate(Collection $template) : void
     {
         $this->templates[] = $template;
     }
 
+    /**
+     * Get templates
+     *
+     * @return Collection[]
+     *
+     * @since 1.0.0
+     */
     public function getTemplates() : array
     {
         return $this->templates;
diff --git a/Models/Price/Price.php b/Models/Price/Price.php
index 11d56b0..4129810 100755
--- a/Models/Price/Price.php
+++ b/Models/Price/Price.php
@@ -14,14 +14,12 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Models\Price;
 
+use Modules\Attribute\Models\AttributeValue;
+use Modules\Attribute\Models\NullAttributeValue;
 use Modules\ClientManagement\Models\Client;
-use Modules\ClientManagement\Models\ClientAttributeValue;
 use Modules\ClientManagement\Models\NullClient;
-use Modules\ClientManagement\Models\NullClientAttributeValue;
 use Modules\ItemManagement\Models\Item;
-use Modules\ItemManagement\Models\ItemAttributeValue;
 use Modules\ItemManagement\Models\NullItem;
-use Modules\ItemManagement\Models\NullItemAttributeValue;
 use Modules\SupplierManagement\Models\NullSupplier;
 use Modules\SupplierManagement\Models\Supplier;
 use phpOMS\Localization\ISO4217CharEnum;
@@ -50,23 +48,23 @@ class Price implements \JsonSerializable
 
     public Item $item;
 
-    public ItemAttributeValue $itemgroup;
+    public AttributeValue $itemgroup;
 
-    public ItemAttributeValue $itemsegment;
+    public AttributeValue $itemsegment;
 
-    public ItemAttributeValue $itemsection;
+    public AttributeValue $itemsection;
 
-    public ItemAttributeValue $itemtype;
+    public AttributeValue $itemtype;
 
     public Client $client;
 
-    public ClientAttributeValue $clientgroup;
+    public AttributeValue $clientgroup;
 
-    public ClientAttributeValue $clientsegment;
+    public AttributeValue $clientsegment;
 
-    public ClientAttributeValue $clientsection;
+    public AttributeValue $clientsection;
 
-    public ClientAttributeValue $clienttype;
+    public AttributeValue $clienttype;
 
     public ?string $clientcountry = null;
 
@@ -93,21 +91,22 @@ class Price implements \JsonSerializable
     public string $currency = ISO4217CharEnum::_EUR;
 
     public ?\DateTime $start = null;
+
     public ?\DateTime $end = null;
 
     public function __construct()
     {
         $this->item        = new NullItem();
-        $this->itemgroup   = new NullItemAttributeValue();
-        $this->itemsegment = new NullItemAttributeValue();
-        $this->itemsection = new NullItemAttributeValue();
-        $this->itemtype    = new NullItemAttributeValue();
+        $this->itemgroup   = new NullAttributeValue();
+        $this->itemsegment = new NullAttributeValue();
+        $this->itemsection = new NullAttributeValue();
+        $this->itemtype    = new NullAttributeValue();
 
         $this->client        = new NullClient();
-        $this->clientgroup   = new NullClientAttributeValue();
-        $this->clientsegment = new NullClientAttributeValue();
-        $this->clientsection = new NullClientAttributeValue();
-        $this->clienttype    = new NullClientAttributeValue();
+        $this->clientgroup   = new NullAttributeValue();
+        $this->clientsegment = new NullAttributeValue();
+        $this->clientsection = new NullAttributeValue();
+        $this->clienttype    = new NullAttributeValue();
 
         $this->supplier = new NullSupplier();
     }
diff --git a/Models/Price/PriceMapper.php b/Models/Price/PriceMapper.php
index 4eaef80..a9ebd83 100755
--- a/Models/Price/PriceMapper.php
+++ b/Models/Price/PriceMapper.php
@@ -16,7 +16,7 @@ namespace Modules\Billing\Models\Price;
 
 use Modules\ClientManagement\Models\ClientAttributeValueMapper;
 use Modules\ClientManagement\Models\ClientMapper;
-use Modules\ItemManagement\Models\ItemAttributeValueMapper;
+use Modules\Attribute\Models\AttributeValueMapper;
 use Modules\ItemManagement\Models\ItemMapper;
 use Modules\SupplierManagement\Models\SupplierMapper;
 use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
@@ -80,19 +80,19 @@ final class PriceMapper extends DataMapperFactory
             'external' => 'billing_price_item',
         ],
         'itemgroup' => [
-            'mapper'   => ItemAttributeValueMapper::class,
+            'mapper'   => AttributeValueMapper::class,
             'external' => 'billing_price_itemgroup',
         ],
         'itemsegment' => [
-            'mapper'   => ItemAttributeValueMapper::class,
+            'mapper'   => AttributeValueMapper::class,
             'external' => 'billing_price_itemsegment',
         ],
         'itemsection' => [
-            'mapper'   => ItemAttributeValueMapper::class,
+            'mapper'   => AttributeValueMapper::class,
             'external' => 'billing_price_itemsection',
         ],
         'itemtype' => [
-            'mapper'   => ItemAttributeValueMapper::class,
+            'mapper'   => AttributeValueMapper::class,
             'external' => 'billing_price_itemtype',
         ],
         'client' => [
diff --git a/Models/Tax/TaxCombination.php b/Models/Tax/TaxCombination.php
index 7473578..333392c 100755
--- a/Models/Tax/TaxCombination.php
+++ b/Models/Tax/TaxCombination.php
@@ -14,12 +14,8 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Models\Tax;
 
-use Modules\ClientManagement\Models\ClientAttributeValue;
-use Modules\ClientManagement\Models\NullClientAttributeValue;
-use Modules\ItemManagement\Models\ItemAttributeValue;
-use Modules\ItemManagement\Models\NullItemAttributeValue;
-use Modules\SupplierManagement\Models\NullSupplierAttributeValue;
-use Modules\SupplierManagement\Models\SupplierAttributeValue;
+use Modules\Attribute\Models\AttributeValue;
+use Modules\Attribute\Models\NullAttributeValue;
 
 /**
  * Billing class.
@@ -39,11 +35,11 @@ class TaxCombination implements \JsonSerializable
      */
     protected int $id = 0;
 
-    public ?ClientAttributeValue $clientCode = null;
+    public ?AttributeValue $clientCode = null;
 
-    public ?SupplierAttributeValue $supplierCode = null;
+    public ?AttributeValue $supplierCode = null;
 
-    public ItemAttributeValue $itemCode;
+    public AttributeValue $itemCode;
 
     public string $taxCode = '';
 
@@ -72,7 +68,7 @@ class TaxCombination implements \JsonSerializable
      */
     public function __construct()
     {
-        $this->itemCode = new NullItemAttributeValue();
+        $this->itemCode = new NullAttributeValue();
     }
 
     /**
diff --git a/Models/Tax/TaxCombinationMapper.php b/Models/Tax/TaxCombinationMapper.php
index e1b0a0f..dbf1c99 100755
--- a/Models/Tax/TaxCombinationMapper.php
+++ b/Models/Tax/TaxCombinationMapper.php
@@ -15,7 +15,7 @@ declare(strict_types=1);
 namespace Modules\Billing\Models\Tax;
 
 use Modules\ClientManagement\Models\ClientAttributeValueMapper;
-use Modules\ItemManagement\Models\ItemAttributeValueMapper;
+use Modules\Attribute\Models\AttributeValueMapper;
 use Modules\SupplierManagement\Models\SupplierAttributeValueMapper;
 use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
 
@@ -67,7 +67,7 @@ final class TaxCombinationMapper extends DataMapperFactory
             'external' => 'billing_tax_supplier_code',
         ],
         'itemCode' => [
-            'mapper'   => ItemAttributeValueMapper::class,
+            'mapper'   => AttributeValueMapper::class,
             'external' => 'billing_tax_item_code',
         ],
     ];