INTRODUCTION TO ASYCUDA++ Ó UNCTAD - SITE (V1.15) 1.11 User Interface The  user  is  presented  with  input  screens  with  icons,  pull  down  menus  and  multiple  level  screens that will be familiar to any user of Windows â . Movement around the screens is facilitated with the use of a mouse, cursor keys, fast-path commands or function keys. The system is provided with a help facility that can be written in country and updated with ease. Should the user wish to access data held on the server then he needs only to request login to the server and enter a valid user name and password. The requests are evaluated and passed on to the system message handler. The majority of people using the system will be totally unaware that they are using the network or another machine. If  the  user  wishes  to  update  data  on  his  local  database,  the  request  is  received,  evaluated  and passed on to the local engine for further manipulation. The user interface is totally divorced from the database  used.  Were  the  ASYCUDA++  platform  to  change,  the  modifications  necessary  at  the user interface level would be minimal. Message handler The message handler that resides on both Client and Server is the crucial link between the user and the system database. This software is totally transparent to the user and to those who develop the  modules  that  use  it.  The  message  handler  is  fully  capable  of  performing  the  validation  and transfer of data between the ASYCUDA++ engine and any appropriate external interfaces. On the client side, the message handler receives requests for SQL data manipulation/retrieval from the  user  interface.  It  structures  those  requests  so  that  they  can  be  sent  across  the  network  in  a format that can be understood by the message handler on the server. There  are  several  phases  involved  in  this  formatting.  The  request  has  to  be  dispatched  with  the correct  requestor  information,  for  instance,  not  all  users  will  have  permission  to  query  sensitive databases.   The   ASYCUDA++   message   handler   is   a   complex   piece   of   software,   but   this   is necessary so that it can allow external applications to use the same tool to pass their own requests across the network. The ASYCUDA++ Server The  ASYCUDA++  Server  is  a  UNIX  driven  machine  that  has  as  its  central  data  repository,  an ‘INFORMIX’  or  ‘ORACLE’  database  containing  all  master  and  transaction  files  required  for  the ASYCUDA++ national set up.  As some of these files also exist at the Client PC level, an integral part  of  the  ASYCUDA++  implementation  is  the  replication  of  the  server  master  files  to  the  local master files used for validation on the Client PC. The Server is capable of being partitioned into several ‘Virtual Servers’ called ‘Engines’. This gives the possibility of running several engines on one piece of Server hardware. Operating System UNIX,  as  well  as  being  a  recognised  standard  for  open  systems,  offers  the  following  additional advantages: ·     UNIX  portability  means  that  the  initial  investment  is  small  and  any  necessary  upgrade  in processing power can occur at a relatively low cost. ·     UNIX  is  the  standard  environment  for  most  computer  oriented  technical  studies  and  so  the recruitment of system supervision personnel is therefore relatively straightforward. Relational Database Management System Informix and Oracle are the SQL databases that can be used on the Server. As the table structure of the reference data on the Server is mirrored by the structure available on the Client, so it follows that the database could be replaced by any other relational database available under UNIX.