Computational environments used by scientists should provide high-level support for scientific processes that involve the integrated and systematic use of familiar abstractions from a laboratory setting, including notebooks, instruments, experiments, and analysis tools. However, doing so while hiding the complexities of the underlying computational platform is a challenge. ViNE is a web-based electronic notebook that implements a high-level interface for applying computational tools in scientific experiments in a location- and platform-independent manner. Using ViNE, a scientist can specify data and tools, and construct experiments that apply them in well-defined procedures. ViNE's implementation of the experiment abstraction offers the scientist an easy-to-understand framework for building scientific processes. This paper discusses how ViNE implements computational experiments in distributed, heterogeneous computing environments.