Motivated by the use of scientific workflows as a user-oriented mechanism for building executable scientific data integration and analysis applications, this article introduces a framework and a set of associated methods for analysing the execution properties of scientific workflows. Our framework uses a number of formal modelling techniques to characterize the process and data behaviour of workflows and workflow components and to reason about their functional and execution properties. We use the framework to design the architecture of a customizable tool that can be used to analyse the key execution properties of scientific workflows at authoring stage. Our design is generic and can be applied to a wide variety of scientific workflow languages and systems, and is evaluated by building a prototype of the tool for the Discovery Net system. We demonstrate and discuss the utility of the framework and tool using workflows from a real-world medical informatics study.