Methods and systems herein employ graphical elements as a coding basis within a development platform to develop Web applications that access and aggregate real-time data of connected devices. The development platform includes testing and development functions to simplify the development of mashup web applications. In one aspect, the platform causes updates of the client-side applications, and the real-time data to be received at each test device with a save action of the development workspace. In another aspect, the platform inserts code to enable caching operations at the client-side applications, based on associative linking of the graphical objects during development. In another aspect, the platform employs multiple-level hierarchical real-time data to enable the client-side applications to maintain client-side cursors of the last presentation state of the data upon an update of the applications.