Hi Suresh,
Compression in Info Cube:
a)When you want to compress data in cube, (say request a ,b & c), then all request will disappers and data is aggreatagated based on key into single request which having request id 0.
b) during compression data move from F-fact tabe to E-Fact table.
Aggreatate in Cube: Aggreate use when u want to increase performance of reporting. Lets say you have bex query which is brings data to you based on company code & plant as input & in output you want only 10 fields in cube(suppose cube having 100 fields). so to un-necessaryily bringing all fields u will create aggreate based o required fields only.. but question is how we get data into this aggreate/ say for 10 fields ... so now Rollup comes into picture...
Compression status in Infocube:
When u do this, data shifted from F to E table, and request id become 0.
Rollup status:
If u do this, data provided to aggreate.. this activity is very important if u are doing any reporting based on aggreate, if u forgot then report always shows old data , in case u miss to do rollup..
Regards,
Hitesh