I give you few notes to start with. 771929 should answer your question on index.
771929 - FAQ: Index fragmentation
Now, in sap you can do indexes built by different means - running report RSORAISQN, RSORAISQN or with BRTOOLS and also directly with sql command alter index ...
712098 - RSORAISQ: Index Storage Quality Management
444287 - Checking the index storage quality
http://help.sap.com/saphelp_nw70/helpdata/en/75/95536a63b44b4a9e7f278c7d9c2b67/content.htm
best regards
ashish