What does the "deductive-nomological model" hold regarding the nature of scientific explanations?

According to this model, the aim of science is to provide explanations of particular observed phenomena by showing that the occurrence of such phenomena can be validly deduced from a collection of several theoretical statements of universal laws and other observation statements describing observable "initial" or "antecedent" conditions. When such a deduction is performed prior to the occurrence of the phenomenon, it is called a "prediction," after the phenomenon has already occurred, it is called an "explanation." However the valid deduction of a single observable phenomenon -or even a very large number of phenomena- from a law does not establish the truth of the law. To say a deduction is "valid" means only that if those laws are true then that phenomenon would occur. Laws themselves can be explained by deduction from "higher level" laws, but that, of course, does not establish the truth of those higher level laws.