I am trying to understand what is the appointment booking workflow in FHIR ? Will I be first querying Schedule resource and then Slot resource ? Is such workflow mentioned anywhere in FHIR documentation and shall I expect my clients to follow it?
There is a brief summary of the scheduling workflow on the appointment page. http://hl7.org/fhir/appointment.html#5.27.1.1
You should also then review the tables that describe some of the common status transitions which gives some guidance on the relationship/meaning between each of the resources. http://hl7.org/fhir/appointment.html#typical
We are also trying to get more complete guidance/worked examples that you can refer to for this purpose, but that is not ready/available at this time.