As moving, disarming, and elusive as one of her classic songs, ''Composed'' is Rosanne Cash's testament to the power of art, tradition, and love to transform a life. For more than three decades she has been one of the most compelling figures in popular music, having moved gracefully from Nashville stardom to critical recognition as a singer-songwriter and author of essays and short stories. Her remarkable body of work has often been noted for its emotional acuity, its rich and resonant imagery, and its unsparing honesty. Those qualities have enabled her to establish a unique intimacy with her audiences, and it is those qualities that inform her long-awaited memoir.