Importing orders to Magento - product_options

Question

I've been tasked with importing from a non Magento store into Magento 1.9. We have over 236k orders that need to be imported. So far I've successfully written services (c#) to manage importing customers, categories, attributes and products directly into mysql. Now I need to do the orders. However, I'm stuck on what the information is in the product_options field that is serialized.

a:1:{s:15:"info_buyRequest";a:2:{s:3:"qty";i:1;s:7:"options";a:0:{}}}

Can anyone point to somewhere that defines what each item is (s:15, a:2, s:3, etc) or explain to me what each item that needs to go into the serialization?

Thanks