We address the problem of rating or comparing navigation algorithms, or more generally navigation packages. For a given environment a navigation package consists of a motion planner and a sensor to be used during navigation. The ability to rate or measure a navigation package is important in order to address issues like sensor customization for an environment and choice of a motion planner in an environment. We develop a framework under which we can rate a given navigation package. Based on the navigation package, a partially observable Markov decision process (POMDP) is defined. Next an optimal policy to be used in this POMDP is searched for. The performance achieved under the resulting policy serves to measure the navigation package. This paper presents the motivations for solving the problem, the model we use and the framework which we have developed. An accompanying paper presents the algorithm which we use and some results.