A Brief History of Liquid Software.

The concept of liquid software, i.e., software with flexible deployment, over the past two decades has appeared in the fields of edge computing, Internet of Things (IoT), Human-Computer Interaction, DevOps and Web engineering. In this paper, we survey, compare, and provide a comprehensive definition of liquid software by analyzing how the metaphor has been used in existing literature and identifying gaps and inconsistencies in the current vs. past understanding of the concept. Overall, liquid software can be seamlessly deployed and redeployed within a dynamic and distributed runtime environment in response to changes applied to the set of available devices and to the software itself. Liquid software has been introduced in the context of active networks and intelligent environments, it has been applied to describe the user interaction with multi and cross-device user interfaces, it has found a promising foundation in Web technology, continuous software delivery pipelines, as well as isomorphic software architectures running across the IoT, edge and Cloud continuum.