IT MIGHT SEEM THAT AMERICAN ETHNIC DIVERSITY is a recent discovery, beginning only after the major work of the civil-rights movement was completed. But from 1929 to 1955 — first on radio and then on TV — white-bread America followed the adventures of the Goldberg family, a first-generation German-Jewish immigrant clan created by writer-star Gertrude Berg. That's the news hook of Yoo Hoo, Mrs. Goldberg, an interesting documentary that stops short of being revelatory.

Written, produced, and directed by D.C. filmmaker Aviva Kempner, who did a similar study of baseball player Hank Greenberg a decade ago, Yoo Hoo is primarily concerned with establishing that Gertrude Berg existed, and that she trailblazed the domestic sitcom. Born Tillie Edelstein in 1898, Berg was a third-generation New Yorker who lacked the Yiddish accent she affected to play Molly Goldberg. Her father was a Manhattan restaurateur who later opened a Catskills resort hotel. As a teenager, Berg involved the guests's kids in skits so their families wouldn't flee the hotel during rainy periods.

After a brief sojourn in Louisiana with her new husband, British-born engineer Lewis Berg, Gertrude Berg began her radio career pitching Christmas cookies in Yiddish, a language she didn't speak. (Yoo Hoo is strong on such absurd details.) A week after the 1929 crash came the debut of a show with the intriguing title of The Rise of the Goldbergs. Two decades later, The Goldbergs — they'd finished rising, apparently — arrived on the CBS TV network. The program was a hit, but didn't last long.

You can probably guess, at least roughly, what happened next. Philip Loeb, who played Molly's husband, was branded a communist sympathizer in 1950. Berg fought for him, and the show. After its cancellation, The Goldbergs returned to the air without Loeb. (He later killed himself, an event fictionalized in 1976's The Front.) But the show ended after the 1955 season, a victim of — well, what? All that Yoo Hoo can offer is that the Goldbergs relocated from the Bronx to the suburbs in their final season, a move that left them (and Berg's scripts) unmoored.

Berg died in 1966, leaving a guarded Person to Person interview with Edward R. Murrow as the principal video evidence of her non-Molly self. Kempner supplements that with testimony of admirers, many of them Jewish media professionals such as Norman Lear and Ed Asner. (Supreme Court Justice Ruth Bader Ginsburg is here, too.) Also, an African-American and a Greek-American fan appear to note that as young fans they identified with The Goldbergs's emphasis on family and education.

The documentary mentions a few episodes that sound remarkable: one show featured excerpts from an actual Passover seder, which was interrupted by a rock thrown the family's window — a reference to Kristallnacht. But Yoo Hoo fails to establish that Berg's use of specific ethnic details or political references was unusual.

Kempner includes a clip of the original Amos and Andy radio show, and notes that The Goldbergs's time slot later went to I Love Lucy, featuring the heavily accented Desi Arnez. But for those viewers who weren't watching TV in the 1950s, let alone listening to radio in the 1930s, the documentary fails to establish the cultural climate. Was Berg's show a rare challenge to white-Euro-Protestant norms? Or were the Depression and WWII eras more open to diversity, an acceptance washed away by the reactionary tide of the 1950s? Or did reminders of old-country folkways — whether Jewish, Italian, Irish, or whatever — simply become an collective embarrassment in the affluent, assimilated postwar era?

These unanswered — indeed, unposed — questions make Yoo Hoo, Mrs. Goldberg somewhat frustrating. The film has command of the facts of Berg's family life (much of which was definitely not sitcom material) and career. Yet the larger context remains vague. The story of The Goldbergs could have been unlocked a larger national saga, but this documentary doesn't look far beyond the window through which Molly Goldberg used to respond to her neighbors's yoo-hoos.

YOO-HOO, MRS. GOLDBERG — 2008, 92 min; at the Avalon Theater.

ONE THING THAT'S CERTAIN ABOUT (500) DAYS OF SUMMER: It doesn't express the viewpoint of its title character, Summer Finn. Whose viewpoint it does express, however, is something of a mystery.

Much of the time, this semi-romantic semi-comedy is about Tom Hanson (Joseph Gordon-Levitt), who went to architecture school but works as a copywriter for a greeting-card company so retro couldn't possibly exist — especially in gentrifying but still boho downtown L.A., which is where the film locates it. Glum, aimless Tom meets vivacious, quirky Summer (a typecast Zooey Deschanel), who's new at the company, and is immediately smitten.

The film is divided into days, which are then shuffled out of chronological order. So the couple's breakup arrives on the heels of their meeting, leaving the rest of the film to function as a prolonged emotional wallow. If Tom is obsessed, Summer is the one who gets the anti-romance started. She grabs Tom in the copier room, and soon they are — in Potterspeak — snogging. Summer temporarily functions as a reasonable facsimile of a girlfriend, but warns Tom that she doesn't want "anything serious." So the split wouldn't come as a surprise, even if we didn't already know about it before it occurs.

(500) Days could have been another diary of a hapless young male romantic, revealing the lovelorn guy's feelings for the woman he (and thus we) will never really understand. But the film employs a third-person narrator, who takes out us of Tom's head — and into self-conscious shtick. A mock-doc aside explains "the Summer effect": as an adorable teenager, she drew lots of admiring customers to various retail businesses. When Tom is sure he's made the connection with Summer, a song-and-dance number begins near the Civic Center Metro station, complete with a Disney-style cartoon bluebird. In another scene, Tom finds himself inside parodies of nouvelle vague and Bergman films.

This isn't Tom's consciousness. It's the movie-movie worldview of director Marc Webb, a music-video veteran who also stuffs the movie with hip and no-so-hip tunes from the Smiths, the Clash, the Pixies, Spoon, Simon and Garfunkel, and Hall and Oates — some of them, for maximum snarkiness, sung in a karaoke bar. Webb's tricks make (500) Days cutesier than the standard Hollywood rom-com, but no less anonymous. Tom remains almost as blank a slate as Summer.

The movie's only distinctive aspect is its use of downtown L.A., which is generally off-limits to Hollywood film crews — unless it's downscaled for ominousness, as in The Soloist, which made the city's skid row look like the eighth circle of Hell. But indie films have walked these streets before. In fact, last year's In Search of a Midnight Kiss visited some of the same locations. But without the goddam animated birdie.

(500) DAYS OF SUMMER — at Landmark Bethesda Row, Regal Gallery Place, and AMC Leows Georgetown.