HR Management vs. Line Management?

Compare HR Management with Line Management.   

What is the role and responsibility of each?   Explain how do they interact?  
Which of these two groups has ownership for employees and employee management and development?

In many organizations today, a typical structure has an HR Business Partner (HRBP) assigned to each major business unit.  

In this case who does the HRBP report to? 
What is the role and  responsibility of the HRBP?    
When there are situations where the Line Management of the Business Unit disagrees with the HRBP, how is that best resolved?  
Also in this HRBP structure, who has hiring, firing, managing, developing, etc. responsibility and authority? – Explain.

As you consider the situations where an HRBP is assigned to a business unit, what do you believe is necessary to assure a positive working relationship between the HRBP and Line Management?

When this arrangement – an HRBP is assigned to a specific Business Unit and the management of that unit ignores or discounts guidance provided by the HRBP and the result may be employee disengagement, negative reactions, conflict, etc. — What should the HRBP do?
Overall do you believe the structure that assigns an HRBP to each key business unit is an effective approach for a business?  If yes, why do you believe so – If no, why not – explain!