Having studied the Separation of Concerns in the previous chapter and reflected on the previous illustration, the following design guidelines help ensure that the Service layer is agnostic of the caller, easy to locate, and encourages some Force.com best practices, such as bulkification. Note that bulkification is not just a concept for Apex Triggers; all the logic in your application must make efficient use of governed resources.
A colleague of mine used to reference the following when talking about naming:
"There are only two hard things in Computer Science: cache invalidation and naming things."
–Phil Karlton
In my career so far, I have come to realize that there is some truth in this statement. Naming conventions have never been so important on Force.com as it is currently without a means to group or structure code files, using a directory structure for example. Instead, all classes are effectively in one root folder called /classes.
Thus...