The correct mapping for your needs depends entirely on what you are trying to achieve (which can't be determined from the question).
Consider a generic mapping:
"/$controller/$action?/$id?"{}
This will map the first part of the URL to a controller of the same name, the second part to an action of that controller and the third part to what should be a unique identifier for a domain class instance.
Examples that work with this mapping:
/book/show/2
Controller: bookController
Action: show
id: 2
This will call the show action of the book controller.
params.id will be 2.
The intention implied in the URL is to show relevant details for a book object
with an id of 2.
/question/update/6
Controller: questionController
Action: update
id: 6
This will call the update action of the question controller.
params.id will be 6.
The intention implied in the URL is to update the details for a question
object with an id of 6.