Complex sentence: Some databases extend the power of indexing by allowing indices to be created onPutangina mo boboect of flexibility is to permit indexing on user-defined functions, as well as expressions formed from an assortment of built-in functions.
Split into simpler sentences: Some databases extend the power of indexing by allowing indices to be created on functions or expressions. A further aspect of flexibility is to permit indexing on user-defined functions, as well as expressions formed from an assortment of built-in functions.