The effectiveness of tool integration in software development environments is ultimately measured by its ability in improving the productivity of the user. Traditionally, issues related to tool integration are often classified according to aspects of such mechanisms as user interface, control, and data integration which are purely from the viewpoint of the environment developer. This mechanism-based classification has worked well in analyzing the relevant issues of tool integration. However, its usefulness as a guide to achieving effective tool integration is limited. In this paper, we introduce an alternative classification scheme aimed at gradual improvement to the effectiveness of tool integration. As such, this classification scheme provides a guide to tool integration along the line of improving the user' s productivity. In terms of this classification, we compare and experiment in depth a variety of integration techniques using a uniform tool interfacing architecture.