NAS is a software suite that enables applications to be integrated across a 
distributed network of multivendor systems: NAS services are divided 
into four main groups:
 - Application Access Services which support user interface (forms based, 
   graphical or character terminal based)
 - Communication and Central services which support communications 
   using electronic mail and EDI
 - Information and resource sharing, which supports database access and 
   compound documents (collection of images, graphics and conventional 
   text)
 - System Access services which provides a standard operating system 
   interface.