>RooCompositeDataStore</tt> has been added that allows to construct composite
     <tt>RooDataSet</tt> objects without copying the input data. 
<pre>
   // Make 2 input datasets and an index category
   RooWorkspace w("w",true) ;
   w-&gt;factory("Gaussian::g(x[-10,10],m[-10,10],s[3,0.1,10])")
   w-&gt;factory("Uniform::u(x)")
   w-&gt;factory("index[S,B]")
   RooDataSet* d1 = w::g.generate(w::x,1000)
   RooDataSet* d2 = w::u.generate(w::x,1000)

   // Make monolithic composite dataset (copies input data)
 