Such convenient arrangements are far less viable under SOA, because applications are turned into services that can have a much broader set of users. The considerable benefit is reuse, but the consequence of that is that the software may need to be available 24/7, or at least for a longer time each day. SOA stomps on the silos, insisting that they co-operate, and the outcome of that can be summed up in one word: dependency.

From Time-Scheduled to Event Driven

Your grandfather’s batch processing was about resource scheduling over the 24 hour cycle, and weekly cycle, and monthly cycle and, in some companies, the annual cycle. It was the same in the siloed world, with the driving force being the need to fit certain workloads within an identifiable time window. In the SOA world scheduling is about dependencies – triggering jobs to run when certain conditions arise. Time can still be a trigger, but so can anything else. You might trigger a job to run when a certain resource (such as disk space) seems to be getting over-used, or you might trigger a job when a specific email has been received or because 10,000 orders have been recorded or, in fact, for any reason.

It is a complex environment and there is a need to distinguish work-flow activities, which naturally belong to the business layer of SOA applications and should normally be specified at that level, and infrastructure activities, which ensure the availability of resources and attempt to ensure that specific workloads have the right amount of resources and don’t cause processing delays. The environment is thus event driven. The driving forces of the environment are business events, and the constraints of the environment are the dependencies between events, service levels and resource availability. And if you are going to orchestrate that, then you need a global scheduling capability.

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