Despite recent improvements in wireless network protocols and the 
manufacturing of better, more performant mobile devices, developing mobile 
applications and services still poses major challenges. Mobile devices have 
scarce computing capabilities, limited storage, short battery lifetime, and 
slow, expensive, and unreliable wireless communication. To alleviate 
these problems, we propose (1) to move the computationally 
intensive operations from the mobile client to an external Web Service and (2) 
to implement efficient data caching on the mobile device to minimize network 
traffic. In this article, we present these two key design aspects in the 
context of a Java development of a mobile service that offers train schedule 
information. The results show better response time and reduced network traffic.