The need for recording time varying information databases has been recognized for quite some time. There have been significant research activities in formulating semantics of time at the conceptual level, developing a model for time varying databases analogous to the relational model for static databases and the design of temporal query languages. It has been argued that a single time attribute is insufficient, and that two time attributes are necessary to fully capture time-varying information. Unfortunately, there has been some confusion concerning terminology and the definition of these time attributes. In this world, a single program performing global query optimization using a cost-based optimizer will not work well. Cost-based optimization does not respond well to site specific type extension, access constraints, charging algorithms, and time-of-day constraints. Since traditional distributed DBMSs have all used cost-based optimizers, they are not appropriate in a WAN environment, and a new architecture is required. Traditional distributed relational database systems that offer location-transparent query languages, such as Distributed INGRES and SDD-1all make a collection of underlying assumptions. Traditional distributed DBMSs do not meet these requirements. Use of an authoritarian, centralized query optimizer does not scale well; the high cost of moving an object between sites restricts data mobility, schema changes typically require global synchronization, and centralized management designs inhibit local autonomy and flexible policy configuration. UML has intentionally been developed as a langue for modeling object-oriented systems. Its use has however widely been spread out. This standardization makes it possible that different vendors produce products that comply with the standard specification.