Familiarizing yourself with the terminology of a relatively new technology component is not only necessary in order to understand the remaining sections of this chapter, but essential to fulfill your responsibilities as an administrator. Let's begin by understanding a simple component diagram, as shown in the following figure, followed by a brief description of each of the components.
Figure 11.3: The component diagram of Enterprise Scheduling Services
A job type is a basic predefined type that indicates what a job would comprise, such as Java or EJB code, PL/SQL, a command line, or web service.
A job definition is the metadata associated with a job, such as parameter values specific to the request being executed.
A job is essentially the smallest unit of work executed by the Scheduler Service engine; it is defined by the associated job type.
A job request is simply the execution of a job definition on a schedule. Every request remains in a WAITING state in the ESS repository.
A job set is a collection of jobs that can either be configured to run concurrently or in a sequence.
A schedule is a predefined time or recurrence for a period of time. Schedules are defined independent of jobs and are used to define when to execute a job request, work assignment, work shift, or purge policy. A schedule can be associated with one or many job definitions to describe when the jobs should be executed. A recurring schedule has a frequency that describes how the moments in time are distributed over time. A recurring schedule can have a start time and an end time to specify the period during which the recurrence should take place.
A work shift defines resources such as threads and throttling that are to be allocated and the duration for which these resources will be available for job requests.
A specialization defines the criteria to select job requests based on parameters such as the user, product, request category, job, or job set.
A work assignment maps a set of work shifts to jobs that are selected through a specialization criterion.
A request dispatcher polls for job requests. For example, the request dispatcher polls the ESS repository for requests that are ready to run, setting their state to READY. The request dispatcher can be enabled or disabled, and the polling interval is configurable.