This Special Issue originates from the Second International Workshop on Scalable Workflow Enactment Engines and Technologies (SWEET), held in conjunction with the 2013 SIGMOD conference in New York, NY, USA on June 23th, 2013. The original idea for the workshop comes from the observation that rapid progress in models and patterns for cloud computing is facilitating a new generation of hybrid database/workflow systems for addressing large data processing problems in a scalable way. Such hybrids are emerging not only in e-science but also for Web-scale data processing, i.e., at Google, Yahoo, and Twitter. At the same time, the core SWEET’13 papers [1,2] report on robust research on core workflow features, including scheduling, distributed engines, and workflows for HPC architectures.
With this in mind, the goal of this special issue was to foster this progress through high quality research in methods, theories, techniques and tools for advancing the Scalable Workflow Enactment Engines and Technologies. Original research articles were solicited in all aspects including architectures, optimization, verification and validation, interfaces and applications of scalable data intensive workflows.

This special issue was completed after an open call that received 13 submissions. After a two-phase peer-review process, the editorial committee selected 8 research and survey papers, which broadly cover three distinct areas within the scope of the special issue. The first two reflect a rather mature research thread, and concern (i) Architectures and (ii) Optimization for scalable workflow enactment. The third group suggests a different angle, with focus on “dynamic steering” of workflows. Here we briefly summarize the papers in each of these three areas.