As knowledgeable about computers as he is about flea markets, Doctorow uses science fiction as a kind of cultural WD-40, loosening hinges and dissolving adhesions to peer into some of society’s unlighted corners. His best known story, ”Craphound,” tells of a competitive friendship between two junk collectors, one human and one alien; what it says about the uses of the past is no more mysterious than the prices paid for a vintage Coke bottle or an early Barbie doll. Not every attempt to wrest truth from cliche works — but you won’t want to miss Doctorow’s satiric glance at co-opted dissent among the grade-school set or the insidious horror of his updated Pinocchio tale.