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THE VISUAL COMPONENT COMPOSITION ENVIRONMENT

The VCCE of the PSE is used primarily to construct applications from software components. In this context, an application is merely seen as a high-level component. The VCCE is used to construct components in the form of a dataflow graph. Once a complete application has been constructed, it is passed to the IRMS to be scheduled on the distributed computing systems available on the network.

In general, a component is a procedural or functional abstraction defined by its input and output interfaces and its semantics. Components have the following properties.

1. Components may be Java Beans or CORBA objects. They may be sequential codes written in Java, Fortran, or C; they may be parallel codes that make use of message passing libraries such as MPI; or they may exploit array-based parallelism through language extensions such as HPJava

2. Components themselves may be hierarchical (i.e. constructed from other components) and be of arbitrary granularity. Thus, a component may perform a simple task, such as finding the average of a set of input values, or it may be a complete application for solving a complex problem.

3. Each component is represented by a well-defined model specified in XML.

4. A component may have individual, group, or world access permissions to specify who may use it.

5. Information is passed from one component to another via uni-directional typed channels. A channel connects an outport of one component to an inport of another component. A component may have zero or more inports. The set of data objects referenced by the channels connected to a component's inport(s) together define its input interface. Similarly, a component may have zero or more outports, and the set of data objects referenced by the channels connected to a component's outport(s) together define its output interface.

6. A set of constraints may be associated with each component, indicating on what platforms it is licensed to run, and whether it requires generic software, such as MPI or the BLAS, to be bound in later in order to run.

7. A performance model is optionally associated with each component. Ideally, this gives the runtime of the component as a function of its input, machine, communication, and network parameters. If no performance model is available, an upper bound on performance can be approximated based on criteria such as the number of inputs/outputs, the implementation language, the execution platform etc. Subsequent executions of the component can be logged into a database, and used to provide a performance model.

8. Information on a component's purpose, the algorithms it uses, and other pertinent explanatory data is optionally associated with a component.

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