JavaCOG Abstraction

Java COG Abstraction

Java COGSpecification. 1

Basic Description. 1

General Abstraction Classes: 2

Additional Abstraction. 3

Basic Description

(from http://wiki.cogkit.org/index.php/Java_CoG_Kit_Abstraction_Guide):

“Every Grid job (remoteexecution, file transfer, file operation) is represented as a Grid task. All job-specific details arerepresented as a task specification.Further, the remote execution and file servers are locally represented as service objects. Every service has a provider attribute associated with it thatsignifies the technology in which the service is implemented. In order toexecute the Grid job, a user needs to create an abstract Grid task andassociate a specification and service to it. The task is then submitted to atask-handler. The task-handler extracts the specification details and dependingon the provider attribute of the service translates them into the protocolspecific constructs expected by the backend service. The task is submitted andexecuted by the handler in an asynchronous mode. Hence, the client need notwait (block) for the task to be completed by the remote service. Instead, oncethe task is submitted to the task-handler, the client is free to continue withother activities and gets asynchronously notified once the task is done(completed or failed).”

General Abstraction Classes:

1          Executable Object:

       AnExecutableObject provides a high-level abstraction for artifacts that can beexecuted on the Grid. It can be specialized as a Grid Task or a TaskGraph.

1.1         Task:

A Task is an atomic unit of execution in cog-abstractions. Itrepresents a generic Grid functionality including remote job execution, filetransfer request, file operation, or information query. It has a uniqueidentity, name, execution status, specification, and set of services (forremote execution).

1.2         TaskGraph

A TaskGraph provides a building block for expressing complexdependencies between tasks. Advanced applications require mechanisms to executeclient-side workflows that process the tasks based on user-defined controldependencies. Hence, the data structure representing the TaskGraph aggregates aset of ExecutableObjects (Tasks and TaskGraphs) and allows the user to definedependencies between these tasks.

2          Specification

Every Grid Taskhas an associated Specification that dictates the objective of the task and theenvironment required to achieve the objective. This class just provides basicattributes which are common to almost all kinds of tasks.

Following three classes are subclasses ofSpecification:

JobSpecification:

The JobSpecification mentions the common parameters needed for theremote job execution independent of the low-level implementation.Implementation-specific parameters can be added to the specification asadditional attributes.

FileTransferSpecification:

    TheFileTransferSpecification provides the commonly used attributes for ?letransfers between Grid resources.

FileOperationSpecification:

The FileOperationSpecification offers the functionality to invokeimportant operations on files hosted on remote Grid resources.

3          Service

Every Grid Taskhas a set of remote Services that support the actual execution of the task. Theservice interface is a local representation of the remote Grid service. Everyservice has a provider attribute that specifies the technology andprovider supported by that service. It also has a service contact and a securitycontext specific to that provider.

4          Handler

Cog-abstractionscontains the TaskHandler and the TaskGraphHandler,to process a Task and a TaskGraph respectively. Once a Task or a TaskGraph issubmitted to the appropriate handler, the handler interacts with the desiredGrid implementation and accomplishes the necessary tasks. The handlers incog-abstractions can be viewed as adaptors that translate the abstract definitionsof a Task and TaskGraph into implementation-specific constructs understood bythe backend Grid services.

5          Status

Every ExecutableObject (Task or TaskGraph) has an associated execution status.

6          Permission

The permissionsinterface provides a means to get and set permissions for a class of usersalong with GridFile and FileResource abstractions.

7          GridFile

A GridFile is anabstract representation of a remote file or directory. It represents the basicproperties of a file such as size, name, modification date, access permissionsetc. This abstraction is a passive information carrier and cannot be used tomodify the properties or contents of a remote resource directly. It can be usedas an input to the file resource abstraction to change access permissions of aremote resource.

Additional Abstraction

If what a userwants to do is manipulate file resources ( read, write, delete, copy …),JavaCOG provides an additional abstraction class which makes the task easier. Inthis case, the user does not need to use task model.

1          FileResource

An alternatemodel of abstraction for file operations, bypassing the task model, isalso available for applications that desire direct interactions with the filehosting Grid servers. A FileResource provides all the necessaryfunctionality to directly invoke remote file operations.