This paper studies five real-world data intensive workflow applications in the fields of natural language processing, astronomy image analysis, and web data analysis. Data intensive workflows are increasingly becoming important applications for cluster and Grid environments. They open new challenges to various components of workflow execution environments including job dispatchers, schedulers, file systems, and file staging tools. Their impacts on real workloads are largely unknown. Understanding characteristics of real-world workflow applications is a required step to promote research in this area. To this end, we analyse real-world workflow applications focusing on their file access patterns and summarize their implications to schedulers and file system/staging designs.