No abstract available.

With the increasing pervasiveness of mobile computing devices, the need to access information in mobile environments has grown rapidly. Consequently, many mechanisms, e.g. broadcast dissemination, hoarding, or specialized caching mechanisms have been developed to overcome the disadvantages of wireless communication systems, which are usually used to access the information. To evaluate such mechanisms a simulation tool is needed that simulates both the users' mobility and their information access patterns. Since most existing user models either model only the mobility or the information access, we developed a new model that covers both aspects. Based on this model, we realized a flexible framework that allows to simulate all aspects of a mobile information access.

With the increasing popularity of mobile computing devices, the need to access information in mobile environments has grown rapidly. Since the information has to be accessed over wireless networks, mobile information systems often have to deal with problems like low bandwidth, high delay, and frequent disconnections. Information hoarding is a method that tries to overcome these problems by transferring information, which the user will probably need, in advance. The hoarding mechanism that we describe in this paper exploits the location dependence of the information access, which is often found in mobile information systems. Our simulation results show that it is beneficial to do so and that we achieve higher hit ratios than with a caching mechanism.

When used in an outdoor environment mobile information systems often suffer from the disadvantages of wireless WANs. Hoarding is a method to overcome these disadvantages by transferring information which is probably needed by the user in advance. Existing hoarding mechanisms are either developed for a certain type of application or do not consider the user's location when selecting the information items to hoard. However, exploiting location information can be of great benefit with respect to the achievable hit-ratios. The hoarding mechanism suggested in this paper is both location-aware and universally applicable. Therefore, it can be used as a generic mechanism in a platform which supports different kinds of mobile information systems. In addition, it can be adapted to different degrees of knowledge about the user's movement.

Due to the lack of a generic platform for location-and spatial-aware systems, many basic services have to be reimplemented in each application that uses spatial-awareness.A cooperation among different applications is also difficult to achieve without a common platform.In this paper we present a platform that solves these problems.It provides an infrastructure that is based on digital models of regions of the physical world, which are augmented by virtual objects.We show how virtual objects make the integration of existing information systems and services in spatial-aware systems easier.Furthermore, our platform supports interactions between the computer models and the real world and integrates single models in a global "Augmented World".