Service Modifier #

Formal Definition: A service modifier is anything that can cause a service's state to transition to another service state, or cause a change of value in at least one of the service variables in a service state.

In practice, service actors such as a customer, an engineer such as an SRE engineer, another service that operates on a service, or the service acting on itself are all considered service modifiers because they can cause a service state to transition to another service state, or cause a change of value in at least one of the service variables in a service state.

In other words, service modifiers mutate service variables.

Using the cloud storage service example, when a user uploads a file, such service will probably transition from UploadRequested service state to UploadInProgress service state while updating the totalUploadedBytes service variable.

Why is a Service Modifier definition important and why not just use a simple concept of a User, Engineer or a Customer? This is so that a definition of a user is clear cut about it being able to modify a service state. By doing this, it effectively includes a "user" in the semantics of a service as a finite-state machine.

Speaking and listening was never a chicken-and-egg situation, the latter must go first to fill the brain. - Anonymous