Some courts publish decisions as a single document that contains all of the opinions (majority, concurrences, dissents) that comprise the decision. Others issue the opinions in different writings. The challenge is to contrive a model that is equally useful in either situation.
The words "decision", "order", "opinion", and "judgment", and even "case" tend to be used both loosely and interchangeably to mean either the act that delivers a court's ruling in a particular case, or the text of the ruling itself. To make things even more confusing, a decision (in either sense) may affect (either dispositively or nondispositively) more than one case, and a decision (in the sense of the text that records the court's ruling) may consist of more than one document.