In this paper, we describe and discuss problems in terms of the music formalization framework that we are developing. Currently, we aim at building a contents design framework for ordinary people in a formal approach. Based on the knowledge representation technology, an art piece and contents are represented by a feature structure and the high-level operations upon the feature structure are available. When we apply the framework to implementing a practical musical system, we face some problems related to algebra, knowledge representation, and/or implementation. These are the issues concerned with: a relative pseudocomplement introduced for increasing descriptive power, an abstraction level of the distance between musical fragments, and a formalization of musical operations in addition to that of musical relations.