The James Joyce connection is explained in detail in Ellmann's (sp?) biography of Joyce. If you're interested, there's a page reference in one of the threads accessible via the link which I posted above.

JJ's wife Nora Barnacle used to sing the song which she had got from her mother, but when he visited Mrs Barnacle in Galway she sang three stanzas more than Nora used to, and these, if I remember correctly, are the stanzas used in "The Dead".