To synchronize MgdSchema?'s features a bit with JCR Node Type Notation, we should support required properties.
If object is being saved without a required field having a value, Midgard should throw an exception and abort that save.
Something like:
<type name="org_openpsa_products_product">
...
<property name="title" type="string" required="yes"/>
</type>
$product = new org_openpsa_products_product();
$product->description = "Blah";
// No title set
$product->create(); // Will throw midgard_error_requiredfield exception and not save the product
