In order to compute metrics automatically, these must be implemented as software programs. As metrics become increasingly complex, implementing them using imperative and interrogative programming is oftentimes cumbersome. Consequently, their understanding, testing and reuse are severely hampered. In this paper we identify a set of key mechanisms that are involved in the implementation of design metrics and, more general, of design-related structural analyses: navigation, selection, set arithmetic, filtering and property aggregation. We show that neither of the aforementioned approaches offers a simple support for all these mechanisms and, as a result, an undesirable overhead of complexity is added to the implementation of metrics. The paper introduces SAIL, a language designed to offer a proper support to a simplified writing of design metrics and similar design-related analyses, with a especial emphasis on object-oriented design. In order to validate the expressiveness of SAIL the paper provides a comprehensive comparison with the other two approaches.