"More-or-less" being the distinguishing factor here. The close relationship of the pulp magazine and pulp novel industries led to many hero-glued fix-ups in other genres of popular fiction (Dashiell Hammett's and Raymond Chandler's early novels, for example); the short attention spans of protosurrealists, pseudosurrealists, and other artistes-fines led to a number of single-hero multiple-narrative (Maldoror, Miss Lonelyhearts) and single-narrative multiple-hero (As I Lay Dying) assortments.

But what defines sf is not a peculiar approach to character or narrative but a peculiar attention to the implied context of the fiction. This implied context is usually called the work's "world," as in the quintessential sf skill "world building" or the quintessential sf hackwork "shared world" writing. Because the constructed context is what defines a "work" of sf, a single sf "work" can cover a great deal of time-space ground (as in Robert Heinlein's "future history") and incorporate many different lead characters and closed narratives.

Given a long enough lifetime, sf authors sometimes start to wonder if all their worlds might somehow be "shared" in the all-in-one person of the author: Isaac Asimov's attempt to combine his Foundation universe with his Robotics universe to make Asimov Universe TM; Samuel R. Delany's multi-decade cross-genre remarks toward the modular calculus....

Outside the sf genre, what this reminds me most of are Jack Spicer's notion of the "serial poem," Louis Zukofsky's notion that a poet's lifetime of work is best considered as one long work, and James Joyce.

(... further reflections generated by the essays in A Collideorscape of Joyce: Festschrift For Fritz Senn ...)

In "Dubliners and the Accretion Principle" Zack Bowen very convincingly treats the collection of mostly-previously-published stories Dubliners "as a single unified work... the stories so interrelated as to form a type of single narrative" with a clear structural pattern and a loose but extensive web of inter-episode linkages. (A biographical tidbit unmentioned by Bowen backs this up: Joyce knew "After the Race" was a weak story but felt compelled to include it to save the overall shape of the book: a common architectural problem for the fix-up author.)

On the next hand, Christine van Boheemen's "'The cracked lookingglass' of Joyce's Portrait" makes a case for breaking apart A Portrait of the Artist as a Young Man, since all the chapters use the same semi-self-contained bump-down-and-bounce-up narrative structure rather than gliding smooth-and-steady towards maturity: "Instead of psychological and emotional growth, the fiction depicts repetition." Each episode imagines itself to be first, last, only and alone whereas it is neither first nor last nor only nor alone in a series originating in and repeated to infinity.... Van Boheemen's approach would imply that the "final" flight to Paris on the wings of artistic vocation is merely another roundabout to the next repetition. And Stephen's bedraggled comedown in Ulysses, so embarrassing to those who pictured him ascending to glory at an angle of fortyfive degrees like a shot off a shovel, certainly seems to give her approach the edge.

There hasn't been much need to remind readers of the heterogeneity of Ulysses, starting from its serialization episode by episode, each episode a chronologically, thematically, and stylistically closed unit. (Are there any other novels for which we refer to "episodes" by title rather than to "chapters" by number?) Timothy Martin reminds us again anyway in "Ulysses as a Whole" that inasmuch as anything can be said to tie the book together it's a shared context -- implicitly an externally documented day in the world, explicitly the inter-episode allusions and reflections, "many of them added late in the book's composition."

As always, the limiting case is Finnegans Wake, whose compositional history also includes serial publication and last-minute blanket-tucking additions. But here the repetition and fragmentation go simultaneously down and up the scale to such an extent that almost no one ever reads the book except as scattered sentence-to-page-sized episodes semi-explained by references to other episodes: "holograms" and "fractals" became rhetorical commonplaces for Wake scholars as quickly as for sf writers.

Maybe that's why Exiles seems like such a flimsy anomaly: it's a self-contained traditionally structured single work where a revue or a burlesque show might have felt more appropriate....