Pegasus and Chimera have been developed as part of the GriPhyN Virtual Data System. Pegasus is designed to map abstract workflows onto the Grid environment. The abstract workflows can be constructed by using Chimera  or can be written directly by the user. The inputs to the Chimera system are partial workflow descriptions that describe the logical input files, the logical transformations (application components) and their parameters, as well as the logical output files produced by these transformations. The partial workflow descriptions are expressed in Chimera’s Virtual Data Language (VDL).

An example of howto write VDL for LIGO can be found here.