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• EDSL Concepts
• Ketrew's Engine

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Glossary

Here are some common terms used in this documentation.

EDSL Concepts

A target (function Ketrew.EDSL.target) is the basic building block of a workflow, a target has many components:

• A build-process wraps a way for a target of running a program, usually on a given host; for example the function Ketrew.EDSL.pbs returns a datastructure representing the action of running a program on a host with the PBS batch scheduler. It is the parameter ?make of Ketrew.EDSL.target.
  • A host (Ketrew.EDSL.Host.t) is a place where one can run things. Usually a host is an SSH host with a “playground”, and a few other options.
  • A playground is a directory on a host where the Ketrew engine and its plugins can (and will) write log files, temporary scripts, etc. Most features which use hosts require playgrounds and will fail if not provided.
  • A program (Ketrew.EDSL.Program.t) is a datastructure representing shell scripts on steroids, Ketrew provides high-level combinators to build programs.
• A condition (Ketrew.EDSL.Condition.t) defines how to tell if a target should be run or not (the argument ?done_when of Ketrew.EDSL.target).
• Links to other targets:
  • dependencies are targets that need to be satisfied or run before a target can start,
  • on-failure-activate targets that will be activated if the target fails, and
  • on-success-activate targets that will be activated only after a target succeeds.
• Metadata and tags are user-provided information; the ?metadata is, for now, just a raw string; the ?tags are a list of strings which are “searchable” (see “filters” sub-menu in the test-user-interface).
• An Equivalence specification tells the engine when to consider a target redundant, the default value is the most common:
  
  • when adding a target, if an active or activable target already has the same condition then the new one is considered redundant and will be replaced with a pointer to the older one;
  • the behavior above can be cancelled by providing `None (cf. Ketrew_pure.Target.Equivalence.t).

In the EDSL, a target may have a product, which is, for now, just a facility for the EDSL itself (the engine does not keep track of products). The ?product argument can be used to track file-paths within your EDSL program (see for example the function Ketrew.EDSL.file_target which just sets the product and the condition of a target for a given file-path; the path can be retrieved with my_target#product#path).

Ketrew's Engine

Ketrew's engine is the process in charge of orchestrating and monitoring the run of the workflows.

• In standalone mode, the command line application has to run the engine manually.
• In client-server mode, the engine is run by the server; the client applications just “submit” workflows.

The engine runs long-running processes through plugins (see documentation).