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Kurator-Akka uses YAML to represent workflow definitions so that workflows can be specified and executed without using any software development tools (other than a text editor) or graphical user interfaces. And other programs can generate workflow specifications simply by producing a YAML file.
See http://yaml.org/ for more information about YAML and a list of libraries in C/C++, Ruby, Python, Java, Perl, C#, and other languages for composing and parsing YAML.
Example workflow