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More than one event cycle can be active at a time, and different event cycles can begin
and end on different read cycles. Multiple event cycles can arise from a single client, as
that client can initiate multiple simultaneous requests. Similarly, multiple event cycles can
arise as a result of multiple clients making simultaneous requests.
Event cycles and read cycles are important concepts that allow applications to specify the time
intervals or event windows for capturing events. Because event cycles can span multiple read
cycles, they enable applications to set up logical, more meaningful observation windows.
Interaction Models
Now that we appreciate the flexibility that the ALE specification affords by distinguishing
between read cycles and event cycles, let’s look at the interaction models available
between a client and an ALE service. The interaction models supported by the ALE specifi-
cation should come as no surprise to application developers: a client can either request
services on demand (synchronous mode) or register for information to be sent to it when
certain conditions are met (asynchronous mode).
Synchronous mode
The primary interaction model is a request/response models, wherein all the method calls
into the ALE service are executed synchronously. Figure 7-6 shows the synchronous
interaction model. The ALE specification supports two modes of interaction in the ...