Context aware ubiquitous technology provides us with much more conveniences in our everyday life by defining contextual information in appropriate ways. Up to now, there has been a vast amount of researches and many context models proposed. Many characteristics have been incorporated into such models such as users, physical locations, available resources, etc. Some also take time factors into consideration. Most still focus on the interactions between context and users/groups rather than discussing follow-up operations deeply. In this study, we extend the scope of the context model to include metadata related to services and use it to describe the behaviours of general operations. Also, by further dividing the time factor into levels of importance, we can use time as the primary control factor to manipulate some specific operations so that operations could be triggered by real time constraints and handled properly. Some critical operations within the whole system may need to be handled by specific users or groups. The occurrence of unexpected situations when the default operator cannot proceed with the corresponding operation on time must be taken care of by a pre-designed time-dependent multi-layer exception handling policy to maintain the integrity and security of the system. We also propose a critical operation scenario, describe the processes of our model and explain the importance of time driven events to prove its applicability.

1. Introduction. As e-communities grow in quality and quantity, online users require more appropriate tools designed to suit their needs and environments. Such tools are not needed in real-world communities where human beings interact with each other directly. Access to context aware ubiquitous content is facilitated by providing intuitive ways for accessing Web content based on the user’s surrounding context [1]. Context, in this case, is any information that can be used to characterize the situation of an entity, where that entity can be a person, place or a physical/computational object [3]. Information can include where and when the web users are, as well as what the web content available nearby is, and so on. It is indeed the context that distinguishes ubiquitous web access from mobile access.