caBIG aims to bring together disparate data and analytic resources into a "World Wide Web of cancer research." This is achieved through common standards and software frameworks for the federation of these resources into "grid" services. Key to the realization of the benefits of Grid computing is the ability to integrate basic services to create higher-level applications. Workflow languages permit such aggregation of services. With such languages, higher-level application can be modeled as graphs where the nodes represent tasks while the edges represent inter-task dependencies, data flow or flow control. Tasks may be performed by basic services. Many of the tasks in the collection and analysis of cancer-related data on the grid involve the use of workflow. Here, we define workflow as connecting of services to solve a problem that each individual service could not solve. caGrid implements workflow by providing a grid service for submitting and running workflows that are composed of other grid services.
caGrid 1.3 provides two workflow execution engines as services: Taverna and ActiveBPEL.
caGrid 1.4 provides only the Taverna workflow engine.
Taverna is an open source domain independent Workflow Management System – a suite of tools used to design and execute scientific workflows.
The Taverna suite is written in Java and includes the Taverna Engine (used for enacting workflows) that powers both the Taverna Workbench (the desktop client application) and the Taverna Server (which allows remote execution of workflows). Taverna is also available as a Command Line Tool that for a quick execution of workflows from a terminal without the overheads of the GUI.
Taverna allows for the automation of experimental methods through the use of a number of different (local or remote) services from a very diverse set of domains – biology, chemistry and medicine to music, meteorology and social sciences.
Effectively, Taverna allows a scientist with limited computing background and limited technical resources and support to construct highly complex analyses over public and private data and computational resources, all from a standard PC, UNIX box or Apple computer.
Using BPEL, Web services can be integrated, using some XML-grammar, to create a higher-level application (business process). A BPEL process is interpreted and executed by an orchestration engine which exposes the process as a Web service. BPEL, which is built on XML-Schema, WSDL and XPath, weaves together basic and structured activities to create the logic of the process.
Use of ActiveBPEL for caGrid Workflow is supported in caGrid 1.3. caGrid 1.4 no longer supports the use of ActiveBPEL.