Addition to existing magento microdata

all I need is to add additional 2 fields to schema , BRAND and MPN both of these are attributes of magento used in products and have values assigned to them I just want them to be in the schema.I suggest that we add these in product page just for these 2 so that they get added to the base schema I need these to be working in schema No global identifier provided (e.g. gtin, mpn, isbn) Missing field 'url' Invalid value type for field 'availability' I need teh schema to be totally perfect for google shopping so make sure you know what you are doing as I will not be sharing any websiet details and you will need to tell me what you need to add and I can do that for you , I know all files structure as existing schema was by me 2 years ago.