I am not so familiar with databases and now I am trying to understand the indexing mechanism.
From what I know, in a RDBMS, indexing on a column makes searching by that column faster. This is also true for the triple stores, only there indices assume you will search(for example) mostly by the subject, then by object and so on.
I am not sure about RDBMS, but on triple stores you can define more than one index, letting the store choose the best index for each query(hopefully I understood this right). Naturally, the following question appears:
Why shouldn't I add all the possible indexes to a triple store, and extending to a RDBMS, why not make indexes on each column(assuming I am not too lazy)?