Differential Caches for Web Services in Mobile Environments


P. Bodorik
M.S. Qaiser
D.N. Jutla

Author Addresses: 

Faculty of Computer Science
Dalhousie University
6050 University Ave.
PO Box 15000
Halifax, Nova Scotia, Canada
B3H 4R2


Although web services have been espoused due to their many benefits, it is known that overhead delay associated with invocation and execution of web services is high. Consequently, much research has been expended on minimizing those delays. In many situations an application invokes a web service repeatedly such that some or most of the data returned by the web service does not change. For instance, many web services that return schedules, such as bus or train schedules, exhibit this property. We use caches to avoid repeated transfer of data sent by a web service to an application, if that data does not change between invocations of the web service. We present Differential Caches with the accompanying Differential Updates method and the Mobile SOAP (mSOAP) protocol. We present two cache designs: one based on the server supporting a cache for each application, while in the other one the server supports a shared cache for all applications. The protocol is flexible in that other optimization techniques, such as encoding, can also be applied with the Differential Updates method. We created a research prototype and performed experiments to evaluate the method’s potential benefits and also its overhead. The results of experiments show clearly that potential benefits outweigh the overhead. The mSOAP protocol with Differential Caches obtained a speedup of up to 800%, in delivery of the web services’ replies in comparison to the SOAP communication. Further improvements in delays were gained when encoding was used in conjunction with Differential Caches.

Tech Report Number: 
Report Date: 
March 30, 2011
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