Only one singer in the world would have the credentials to be the wedding singer whenBarbra Streisand walked down the aisle, and that singer, of course, was Barbra Streisand. But Streisand did turn to someone else to write the song, Chicago’s own Ann Hampton Callaway, who penned “I’ve Dreamed of You” for the special day. But that’s not the only thing these singers have in common. They also share a love for the great composer Harold Arlen, best known for writing the songs from The Wizard of Oz. Arlen wrote the liner notes for Streisand’s very first album, and four years later when he made a record of himself singing his own songs (Harold Sings Arlen—With a Friend) in 1967, he invited “his favorite singer,” Streisand, to be the only other voice on the record. She recorded two songs: the melancholy “House of Flowers” and a romping duet with Arlen himself on “Ding Dong the Witch Is Dead.” Now Callaway is tackling Arlen’s great songbook—which includes “Blues in the Night,” “Stormy Weather,” “Accentuate the Positive,” “I Got the World on a String” “Getty Happy” (which Judy Garland famously sang in counterpoint to Streisand’s singing “Happy Days are Here Again”) and so much more—in a tribute to the composer with the John Pizzarelli Quartet and the Chicago Symphony Orchestra at 5 p.m. Sunday, Aug. 5, at Ravinia.