Rule based adaptation in mobile database systems

Adapta t ion has been identified as one of the key requirements of mobile systems. This demand concerns all components of the mobile system. In this paper, we report on a framework offering adapta t ion in mobile da tabase systems. The framework is based on an optimisat ion model tha t considers adapta t ion as the task of finding an opt imal solution to the problem of configuring the mobile system. This approach allows to reuse existing techniques and offers a uniform handling of system level and application level components. The realisation of the system is based on rules as available in active database systems. This offers a good oppor tuni ty to realise an adaptable system using a rule-based language and allows to solve related problems. The application of the framework is outlined using the example of a workflow management system incorporat ing mobile users. 1 I n t r o d u c t i o n Adapta t ion is one of the core mobile system requirements. The fixed behaviour of s ta t ionary system does not offer adequate suppor t for varying demands concerning the technical environment (such as network and power connectivity) or the non-technical environment (such as nearby people). Consequently, we have to look for appropr ia te models describing the demands of mobile applications and the capabilities of mobile systems with respect to their adaptat ion. These models should be suited as a basis for au tomat ically determining a well-adjusted s tate of the mobile "'Permission to make digital or hard copies of part or all of this work for personal or classroom t, se is granted without lee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is pcrmittcd. To cop5' otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a lee. '" t2, 1997 ACM 0-89791-850-9 97 0002 3.50 310 system regarding its current environment. Furthermore, we have to investigate how we may actually implement the adapta t ion of mobile systems after an acceptable sett ing for the adaptable system components has been determined. In this paper, we describe a rule based solution to these two problems. Both tasks will be tackled using studied techniques. Modelling adapt ive mobile systems can be considered as finding an opt imal configuration of its adjustable system components . The actual runt imeadaptat ion of the mobile system is considered as the suitable modification of the systems behaviour in reaction to occurring events. This can be achieved by using the rule based system specification offered by the technology of active database systems. Furthermore, the use of triggers as available in active database systems for managing mobility has, for example, been proposed in [7] and [9]. In both papers, the active rule system is used to offer the mobile user a way to be notified about interesting events happening outside his current domain. If we broaden the meaning of "notifying", we could also capture an update of the system behaviour in reaction to the changing environment under this term. We use the task of application part i t ioning to outline the use of our system. By application parti t ioning we mean the distribution of the application functionality between mobile and s ta t ionary computers . Other terminology as well as our understanding of mobile comput ing and active database systems is briefly sketched in the next section. Section two also describes existing work in the area of adapta t ion in mobile systems. In section three, we describe a framework for the configuration of mobile systems. A description of possible suppor t for mobile clients in and through active da tabase systems is discussed in section four. An example of the integration of mobile clients into workflow management systems based on active database technology is discussed in section five. : . ::. -. --4 . °O" ~ "~ . *° Wireless c~ll 8 Disconncc~d Wireless cell