Object tagging systems such as Radio Frequency Identification (RFID) enable 
the implementation of a wide variety of ubiquitous computing applications. Up 
to date, most of these prototypical applications have been implemented from 
scratch. Our goal is to develop concepts and software frameworks to ease the 
development of such applications. In this paper we present our experience 
with with a collection of prototypical ubiquitous computing applications based 
on tagged physical objects. We point out a number of basic tasks common to 
this kind of application, before presenting design concepts that we have found 
useful for structuring and implementing such applications. Building upon these 
concepts, we are creating software infrastructures to support the development 
of tag-based ubiquitous computing applications.