add table concept doc

doc/concept.rst

@@ -7,5 +7,6 @@ Concept
    concept/data
    concept/import_data
    concept/schema
+   concept/table
    concept/api_versioning
    concept/authentication

doc/concept/table.rst

@@ -0,0 +1,96 @@
+
+Table
+=====
+
+Abstract
+--------
+
+The PSX table classes offern an alternative to an ORM. Each table class
+represents an sql table. The table class contains the table name and all 
+available columns. It is also the place where you put all complex business 
+queries like in an repository. To get an first impression here an example:
+
+.. code-block:: php
+
+    <?php
+
+    namespace Acme\Table;
+
+    use PSX\Sql\TableAbstract;
+
+    class Comment extends TableAbstract
+    {
+        public function getName()
+        {
+            return 'psx_handler_comment';
+        }
+
+        public function getColumns()
+        {
+            return array(
+                'id' => self::TYPE_INT | self::AUTO_INCREMENT | self::PRIMARY_KEY,
+                'userId' => self::TYPE_INT,
+                'title' => self::TYPE_VARCHAR,
+                'date' => self::TYPE_DATETIME,
+            );
+        }
+    }
+
+Inside an controller you could use the table class in order to get all comment 
+entries
+
+.. code-block:: php
+
+    <?php
+
+    namespace Acme\News\Application;
+
+    use PSX\ControllerAbstract;
+
+    class NewsController extends ControllerAbstract
+    {
+    	/**
+    	 * @Inject
+    	 * @var PSX\Sql\TableManager
+    	 */
+    	protected $tableManager;
+
+    	public function doIndex()
+    	{
+    	    $comments = $this->tableManager->getTable('Acme\Table\Comment')->getAll();
+
+    	    $this->setBody(array(
+    	    	'comments' => $comments,
+    	    ));
+    	}
+    }
+
+If you have complex queries it is best practice to put such queries inside the 
+table class where you can reuse the method across your application. Here an
+fictional method which returns the best comments
+
+.. code-block:: php
+
+    <?php
+
+    class Comment extends TableAbstract
+    {
+        // ...
+
+        public function getBestComments($userId)
+        {
+            $sql = '   SELECT id,
+                              title,
+                              content
+                         FROM psx_handler_comment comment
+                    LEFT JOIN psx_handler_comment_rating rating
+                           ON rating.comment_id = comment.id
+                        WHERE comment.user_id = :user_id
+                     ORDER BY rating.value DESC
+                        LIMIT 8';
+
+            return $this->connection->fetchAll($sql, array(
+            	'user_id' => $userId,
+            ));
+        }
+    }