@victorlin what's your thinking behind suffixing all the models with Model (e.g. `SubscriptionModel`) and then also including the type in the method name? 

This seems very verbose:

```python
from billy.models import SubscriptionModel

subscription = SubscriptionModel.create_subscription(...)    
subscription = SubscriptionModel.get_subscription_by_guid(xxx)
subscription.update_subscription(...)
```

To me, calling the model `Subscription` and the methods `get` and `update` respectively seems more concise and it doesn't detract from readability.