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The Grid system is only used by a client in the central office to start the
scheduling engine that then activates the grid system. The grid system is also a 3-tier
architecture of the following: Client, Commodity Grid (CoG), and Globus Grid
Environment (Grid).
The Client tier is the interface between users and the grid system. It is
responsible for receiving command to run the scheduling engine.
The CoG tier acts as an interface between the Grid and Client tier. Using the
facilities provided by the API, the CoG is able to allow secure file transfers and also
takes the responsibility of job scheduling and monitoring the status of jobs. There is
one job for centralized course scheduling, and many other jobs for decentralized
course scheduling. When a job needs to be performed, the CoG will look for available
nodes to assign it to. The Management and Discovery Service (MDS) provided by the
Globus Toolkit will provide information about the available nodes within the Grid.
Next, it checks and locates the sequence data to available machines (nodes).
Security (GSI) and reliability is important when transferring data to various nodes
within the Grid. In order to provide for such requirements, the Globus Toolkit
provides a data management component, known as Grid Access to Secondary Storage
(GASS), for secure and reliable data transfers. It uses the GridFTP protocol to
facilitate the checking and transport of data files.
The CoG tier monitors the progress of each job and polls regularly to check if
the jobs are finished. The Grid Resource Allocation Manager (GRAM) provides the
necessary services for these processes. Once compiled, the results will be stored into
the database, and their status will be shown to the Client.
3.5 The Database Design
In the database design, we present an entity relation diagram, shown in Figure
3-5. This design also helps us understand more clearly the system requirements.
Data relations between the entities in the above diagram are very important.
Since the course scheduling programs will not work directly on the database, it works
on the data structures instead. Therefore, the data and its relations need to be loaded
from the database into the corresponding data structures before scheduling. The