Some of these are ancient and others were composed more recently as adaptations of popular Arabic songs; sometimes they are written or commissioned for particular occasions, and contain coded allusions to the name of the person honoured. There is a standard Pizmonim book called "Shir uShbaha Hallel veZimrah", edited by Cantor Gabriel A. Shrem under the supervision of the Sephardic Heritage Foundation, in which the hymns are classified according to the musical mode (maqam) to which the melody belongs. As time passes, more and more pizmonim are getting lost, and therefore efforts are being made by the Sephardic Pizmonim Project, under the leadership of Dr. David M. Betesh, to preserve as many pizmonim as possible.