This thesis describes the design of a system to integrate data access and various forms of data analysis and editing tools. -sets of operations-, under a single interactive user interface. The projected system is called YANUS (Yet ANother Unifying System). One of the major goals of this study is to create an environment for the user where he/she1 has optimal freedom to combine operations and apply these directly to his data, and where he is being supported to do so correctly. i.e. in conformance with the meaning of the data and of the operations. Direct application means that the user does not need to copy or transform the data. Another major goal is the encapsulation of existing external systems. Certain operations may, without the user's knowledge, be executed in these existing systems. Also, data to which operations are applied may be stored in existing databases. Thus. the user should be able to analyze data from existing databases with existing tools with minimal effort. He does not need to know about the different interfaces of different systems and about possible data translations. Finally, the environment must be extensible. with respect to the data and operations which may be accessed by the user. and with respect to the databases and software packages to be used to provide data and operations in the integrated system. The main hypothesis supported in this thesis is. that a powerful self-descriptive object-oriented data model can play a central role in achieving these goals.