Why do we need BODS on top of SAP MDM for Data Quality

Hi,

can any one please help me to understand below points.

1.Why do we need BODS on top of SAP MDM for Data Quality.

2.Why do we need Information steward (IS) for data quality reports , even though we can take DQ reports from BODS.

3. what are the IS, BODS and MDM role in implementig gloabl master data management solution.

Thanks,

Deepthi