function sArt(s){
/* s should have the structure 
    {    name:, 
        nails:[{s:{x:,y:},e:{x:,y:},n:},...],
        strings:[{n1:,n2:,se:,c:,th:},...],
        nFlag:
    } 
    where 
        name = name to identify the design, 
        nails = array of nail groups,
        nails[i].s = coordinates of starting nail of i-th nail group,
        nails[i].e = coordinates of ending nail of i-th nail group,
        nails[i].n = number of nails in i-th nail group,
        strings = array of strings,
        strings[i].se = 0 if start nail is mapped to start nail of the groups,
        strings[i].n1 = index of the first nail group in nails array for i-th string group,
        strings[i].n2 = index of the second nail group in nails array for i-th string group,
        strings[i].c = colour of strings for i-th string group,
        strings[i].th = thickness for strings in i-th group,
        nFlag = 0/1 flag to enable or disable the display of nails.
*/
    function drawNails(sa){
        sa.nails.forEach(function(d){ 
            var nr = 2;// nail radius
            var p = d3.range(0,d.n+1).map(function(i){ 
                        return {x:d.s.x+(i/d.n)*(d.e.x-d.s.x),y:d.s.y+(i/d.n)*(d.e.y-d.s.y)};
                    });
            d3.select("#nails").append("g").selectAll("circle").data(p).enter().append("circle")
                .attr("cx", function(d){ return d.x;}).attr("cy",function(d){ return d.y;})
                .attr("r",nr);
        });
    }

    function drawStrings(sa){
        sa.strings.forEach(function(d){
            var s1=sa.nails[d.n1].s;
            var e1=sa.nails[d.n1].e;
            var s2= d.se==0? sa.nails[d.n2].s : sa.nails[d.n2].e;
            var e2= d.se==0? sa.nails[d.n2].e : sa.nails[d.n2].s;
            //assume sa.nails[d.n1].n == sa.nails[d.n2].n;
            var p = d3.range(0,sa.nails[d.n1].n+1).map(function(l){
                return {x1: s1.x + (l/sa.nails[d.n1].n)*(e1.x-s1.x),
                        y1: s1.y + (l/sa.nails[d.n1].n)*(e1.y-s1.y),
                        x2: s2.x + (l/sa.nails[d.n1].n)*(e2.x-s2.x),
                        y2: s2.y + (l/sa.nails[d.n1].n)*(e2.y-s2.y),};
            });
            d3.select("#strings").append("g").selectAll("line").data(p).enter().append("line")
                .attr("x1",function(t){return t.x1;}).attr("y1",function(t){return t.y1;})
                .attr("x2",function(t){return t.x2;}).attr("y2",function(t){return t.y2;})
                .style("stroke", function(){ return d.c}).style("stroke-width", function(){ return d.th;});
        });
    }
    
    if(s.nFlag==undefined || s.nFlag==1) drawNails(s);
    drawStrings(s);
}