Not sure if I completely understand what you mean, but the benefit of a sparse matrix is that zero-valued elements are made implicit by the absence of that (row

Not sure if I completely understand what you mean, but the benefit of a sparse matrix is that zero-valued elements are made implicit by the absence of that (row, column) relation in the database. The drawback is that you need to store a (row, column) for every non-zero-value. It would be wasteful to use this approach for non-sparse matrices, but it would still "work".