Difference between defined benefit plan and defined contribution plan

Hi sir, as I am doing exam questions I found that I really don’t understand about the difference of the two schemes in particular why there is no asset and liability recognised over the defined contribution plan. Since I understand that the contribution is debited for an expense and credit for cash in the company’s perspective. I also understand there is no liability should be recognised since the company is not guranteed for the benefits of the employee. But why the contrbition is expensed, since it is not paid to the employees yet, shouldn’t it be recognised as an asset as well?

I have one hypothesis that the company has signed a contract with external party who runs the fund for them. so probably this is why it is expensed as they regard this as part of the service paid to an outsider just like insurance? on the contrary defined benefits scheme is a one that is runned by company itself internally? I am not sure if I am right about it.

Thank you for your time!