A client server architecture for customized graphical user interfaces on the client side

This thesis treats the generation of customized graphical user interfaces for restricted client devices, which are mainly characterized by severe limitations in terms of processing power, available memory, and input/output interface. Since the late 1990s devices like mobile phones, PDAs, etc. have proliferated in the consumer and embedded market. In the beginning, these limited devices could hardly access Web content and other network services on the application layer, since the Internet technology and its provided services like the World Wide Web (WWW) have originally assumed networked clients with sufficient system resources. Whereas the industry has mainly concentrated on drastically increasing the hardware capabilities of such handheld devices, the approach of this thesis takes particularly the severe hardware restrictions into consideration. The attempt to save hardware resources as much as possible has become an essential part of the emerging initiative called Green Computing. As a result, this thesis proposes a uniform client-server architecture that enables a wide variety of client-devices to access Web content, from very lowend devices like wristwatches to mobile phones and even high-end workstations. The generation of graphical user interfaces for restricted clients with small displays imposes technical as well as ergonomic challenges. This thesis focuses on the technical aspects. On the client side, a new and low-level binary format for describing graphical user interfaces is presented. This format is independent of any particular layout design and takes into account from scratch the different rendering and display capabilities of the restricted client devices by allowing user interface descriptions of different complexity. This new format does not depend on other formats and technologies. In addition, a new virtual machine, called Client Virtual Machine (CVM), is introduced which runs on the client device. The main tasks of the CVM are to communicate with the server, called CVM packet server, and to interpret the received CVM packets, which contain the user interface descriptions. The main design goal of the CVM is a simple and modular architecture so that small and restricted client devices can implement it without large efforts. In contrast to the recent developments in the area of handheld, mobile, and embedded devices, which came along with rising costs for their development and manufacturing, the CVM focuses particularly on very cheap client devices for the mass market to keep the per-unit manufacturing costs as low as possible. On the server side, an exemplary framework for the generation of client-specific user interfaces is presented. After a client request, client-specific user interfaces are generated from an abstract user interface description and from the obtained profile data about the client capabilities such as screen dimensions, memory size, etc. The service providers can decide on their own how they create appropriate CVM packets for the requesting clients. This thesis proposes a technical platform that leaves the service providers as much flexibility and also responsibility in layout-related and other ergonomic issues as possible. For the client-server communication a simple application protocol, called the CVM packet transfer protocol (CPTP), is proposed. It runs on top of the transport layer and is a very “thin” counterpart to the HTTP protocol, which is used in the WWW. Mainly, it consists only of a few protocol methods for requesting and delivering CVM packets and for sending profile data about the client capabilities. The proposed concepts do not depend on Java-, XML-, or WAP-based technologies. They have been implemented in the C programming language and are demonstrated by several examples.