Added Specification pattern

Specification/Not.php

@@ -0,0 +1,34 @@
+<?php
+namespace DesignPatterns\Specification;
+
+/**
+ * A logical Not specification
+ */
+class Not extends AbstractSpecification
+{
+
+    protected $spec;
+
+    /**
+     * Creates a new specification wrapping another
+     * 
+     * @param SpecificationInterface $spec
+
+     */
+    public function __construct(SpecificationInterface $spec)
+    {
+        $this->spec = $spec;
+    }
+
+    /**
+     * Returns the negated result of the wrapped specification
+     * 
+     * @param Item $item
+     * 
+     * @return bool
+     */
+    public function isSatisfiedBy(Item $item)
+    {
+        return !$this->spec->isSatisfiedBy($item);
+    }
+}