The growth of innovative services backed up by various sensors and devices provides an unprecedented potential for ubiquitous computing applications and systems. However, in order to benefit from the recent developments, the current service middleware technology needs a catch-up of being able to fully support interactions among the services. OSGi is considered as a viable service framework solution due to its ability to deal with the dynamism inherent with ubiquitous cloud environments. iPOJO has also emerged as a service component model that simplifies the development of OSGi applications. However, the technology runs short of providing adequate support to foster declarative service compositions of realistic interaction topologies. Noticing this deficiency, we propose an iPOJO component-based service workflow architecture, named iPOJO Flow, where component services can easily be composed together to form realistic, complicated applications. Along with the architectural design, the paper also introduces a new DSL to specify service workflow topologies in a declarative way. The effectiveness of our proposed approach is validated through a prototype demonstration, comparative design analysis, and performance experiments.