The optimization of batch processes has attracted attention in recent years because, in the face of growing competition, it is a natural choice for reducing production costs, improving product quality, meeting safety requirements and environmental regulations. This paper starts with a brief overview of the analytical and numerical tools that are available to analyze and compute the optimal solution. The originality of the overview lies in the classification of the various methods. The interpretation of the optimal solution represents the novel element of the paper: the optimal solution is interpreted in terms of constraints and compromises on the one hand, and in terms of path and terminal objectives on the other. This characterization is key to the utilization of measurements in an optimization framework, which will be the subject of the companion paper.