Recent studies recognize that health is influenced broadly by a multitude of factors of different types, including medical, genetic, environmental, social and behavioral factors. Developing successful health interventions therefore requires taking into account all these factors as well as the interactions between them. However, intervention designers have traditionally had access only to a very limited subset of health data (typically medical record data). Other health data, such as environmental or physical activity data, although already collected and stored, have been very difficult to access, since they are maintained by different providers and isolated in their own proprietary silos. This prevents physicians and intervention designers from acquiring a true overview of all factors influencing a condition and acting towards its prevention or cure. To solve this problem, we propose DELPHI: a platform allowing the integration of disparate health data into a single Whole Health Information Model (WHIM), providing a 360-degree view of an individual's health. DELPHI supports the integration of data and thus enables the design of applications and services that utilize the WHIM to offer the next generation of health services. In this paper, we describe DELPHI's architecture, outline the technical challenges encountered and describe an asthma management use case that will be enabled by DELPHI.