php serialization format when implementing Serializable interface

Question

I understand the serialization format for objects but want to understand the format when Serializable interface is implemented

For example when I serialize an object I get property name as well

"O:21:"Concepts\Cache\Rumble":1:{s:27:"\000Concepts\Cache\Rumble\000data";s:8:"database";}"

But when I implement Serializable I get

string(49) "C:21:"Concepts\Cache\Rumble":15:{s:8:"database";}"

What do I need to do if I want to have property names also in above output?

Thanks