The modeling language did not include any explicit service end concept.
The execution of the service ends when the last element in the ?¬‚ow is reached and
performed. At this stage, a CPL server takes the resulting action and the service ends.
The ?¬‚ow of a call was divided into two parts. The main service ?¬‚ow, described
using a directed relationship, was called Default path. The name was taken directly
from the CPL schema. To model alternative binary choices with the switch concept, an
Otherwise relationship was added to the language. Later, dedicated relationships for
both Proxy and Lookup were added to extend the default path to specify the prede?¬?ned
kinds of outputs. Default or Otherwise relationships could not be used as they did not
have properties to specify outputs. Adding them to the current relationships was
abandoned as that would make the language more complex to use: a modeler would be
asked about design data that could be unnecessary. To make modeling easier and hide
complexity, these choices were put directly into the metamodel.
LANGUAGE FOR MODELING CALL PROCESSING SERVICES 107
Model Layering with Subactions CPL identi?¬?es two layers to support reuse
and modularity. The main action is treated as a topmost action that is triggered, via the
Root element, when events arrive at the server.
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