We address the issue of expressing and evaluating quality rules on music notation. Since music engraving is a highly flexible process that can hardly be constrained by universal principles and rules, score production still heavily relies on the user expertise in order to make context-dependent decisions. We therefore propose a quality management approach based on a formal modeling of this expertise. We show how to use such a model to express context-aware rules that can be evaluated either a priori to prevent the production of faulty notations, or a posteriori to assess quality indicators regarding a score or a corpus of scores. The paper proposes a simple ontology for musical notation, shows how quality rules can be formally stated and evaluated, and illustrates the approach with examples drawn from a large digital library of scores.