With the widespread adoption of the Internet Of Things (IoT), billions of devices are now connected to the Internet and can reach computing facilities along the Cloud- IoT continuum to process the data they produce. This led to a dramatic increase in the deployed IoT-based applications as well as in the data they need to crunch. Those applications oftentimes have Quality of Service (QoS) requirements to be met by determining suitable placements for all processing and data services they are made of, and software-defined routings across the IoT and all different application components. Following a continuous reasoning approach, this thesis proposes a modelling of Cloud-IoT infrastructures and multi-service applications which separately models processing and data storage services, and a methodology that permits determining eligible service placements and data traffic routings over Cloud-IoT resources. A sim- ulated use case is used to assess applicability of the open-source Prolog prototype of the devised methodology.