Locally inverse semigroups are regular semigroups whose idempotents form pseudo-semilattices. In this article, we describe the structure of locally inverse semigroups using Nambooripad's cross-connection theory. We characterise the categories involved as 'unambiguous categories' and provide a new structure theorem for locally inverse semigroups. Further, recall that there are two major structure theorems involving special classes of locally inverse semigroups: inverse semigroups (ESN Theorem via inductive groupoids) and completely 0-simple semigroups (via Rees matrix construction); they seem unrelated. In this article, we specialise our cross-connection description of locally inverse semigroups to these classes to exposit a unification of these different approaches to the structure theory of semigroups. In particular, we show that the structure theorem in inverse semigroups can be obtained using only one category, quite analogous to the ESN Theorem; in a completely 0-simple semigroup, we show that the cross-connection coincides with the structure matrix.