Supporting Mobility in Content-Based Publish/Subscribe Middleware 

Ludger Fiege (1), Felix C. Gärtner(2), Oliver Kasten(3), and Andreas 
Zeidler(4) 

1 Darmstadt University of Technology (TUD), Department of Computer Science 
Databases and Distributed System Group, D-64283 Darmstadt, Germany 
{fiege,az}@dvs1.informatik.tu-darmstadt.de 

2 Swiss Federal Institute of Technology (EPFL) School of Computer and 
Communication Sciences Distributed Programming Laboratory, CH-1015 Lausanne, 
Switzerland fcg@acm.org 

3 Swiss Federal Institute of Technology (ETH Zurich) Department of Computer 
Science, Distributed Systems Group CH-8092 Zurich, Switzerland 
oliver.kasten@inf.ethz.ch 

Abstract. Publish/subscribe (pub/sub) is considered a valuable middleware 
architecture that proliferates loose coupling and leverages reconfigurability 
and evolution. Up to now, existing pub/sub middleware was optimized for static 
systems where users as well as the underlying system structure were rather 
fixed. We study the question whether existing pub/sub middleware can be 
extended to support mobile and location-dependent applications. We first 
analyze the requirements of such applications and distinguish two orthogonal 
forms of mobility: the system-centric physical mobility and an 
application-centric logical mobility (where users are aware that they are 
changing location). We introduce location-dependent subscriptions as a 
suitable means to exploit the power of the event-based paradigm in mobile 
applications. Briefly spoken, location-dependency refines a subscription to 
accept only events related to a mobile user's current location. 
Implementations for both forms of mobility are presented within the 
content-based pub/sub middleware REBECA, drawing from its refined routing 
capabilities (namely, covering and merging). 
 LNCS 2672, p. 103 ff.