Added Specification pattern

Specification/SpecificationInterface.php

@@ -0,0 +1,38 @@
+<?php
+namespace DesignPatterns\Specification;
+
+/**
+ * An interface for a specification
+ */
+interface SpecificationInterface
+{
+    /**
+     * A boolean evaluation indicating if the object meets the specification
+     * 
+     * @param Item $item
+     * 
+     * @return bool
+     */
+    public function isSatisfiedBy(Item $item);
+
+    /**
+     * Creates a logical AND specification
+     * 
+     * @param SpecificationInterface $spec
+
+     */
+    public function plus(SpecificationInterface $spec);
+
+    /**
+     * Creates a logical OR specification
+     * 
+     * @param SpecificationInterface $spec
+
+     */
+    public function either(SpecificationInterface $spec);
+
+    /**
+     * Creates a logical not specification
+     */
+    public function not();
+}