% $OpenXM: OpenXM/doc/issac2000/openxm-stackmachines.tex,v 1.2 2000/01/02 07:32:12 takayama Exp $

\section{OpenXM Stackmachines}   (Tamura)

In OpenXM specification, all servers are stackmachines.
These are called OpenXM stachmachines.
When a server ox\_xyz gets a OX data message,
it translates the data into its own object and push the object
on the stack.
The translation scheme together with mathematical operation definitions
of the system ox\_xyz is called the {\it phrase dictionary} of
ox\_xyz following the idea of OpenMath.

OX command message starts with the int32 tag OX\_COMMAND.
The body is OpenXM stackmachine operation code expressed by int32.
The codes are listed below.
\begin{verbatim}
#define SM_popSerializedLocalObject               258
#define SM_popCMO                                 262
#define SM_popString                              263
#define SM_mathcap                                264
#define SM_pops                                   265
#define SM_setName                                266
#define SM_evalName                               267
#define SM_executeStringByLocalParser             268
#define SM_executeFunction                        269
#define SM_beginBlock                             270
#define SM_endBlock                               271
#define SM_shutdown                               272
#define SM_setMathCap                             273
#define SM_executeStringByLocalParserInBatchMode  274
#define SM_getsp                                  275
#define SM_dupErrors                              276
#define SM_DUMMY_sendcmo                          280
#define SM_sync_ball                              281
#define SM_control_kill                          1024
#define SM_control_to_debug_mode                 1025
#define SM_control_exit_debug_mode               1026
#define SM_control_reset_connection              1030
\end{verbatim}

OpenXM does not have a standard for mathematical operation sets
while it is one of the main future projects of \cite{gap}.
Each OpenXM server has its own mathematical operation set.
Mathematical operator name, such as fctr (asir factorization command),
is pushed as a string,
SM\_executeFunction pops the operator name, the number of arguments
and arguments,
evaluates the operator, and pushes the result on the stack.
For example, the following code factorizes $x^{100}-1$ by calling
ox\_asir.
\begin{verbatim}
P = ox_launch(); 
ox_push_cmo(P,x^100-1); ox_push_cmo(P,ox_int32(1));
ox_push_cmd(P,269); 
Ans = ox_pop_cmo(P);
\end{verbatim}

When an error has occurred on an OpenXM server,
an error object is pushed to the stack instead of a result of the computation.
The error object consists of the serial number of the OX message
which caused the error, and an error message.
\begin{verbatim}
[341] ox_rpc(0,"fctr",1.2*x)$
[342] ox_pop_cmo(0);
error([8,fctr : invalid argument])
\end{verbatim}

Errors are not sent to the client except a SM\_pop* command is received.
Open XM stackmachines works in the asynchoronous mode which is similar 
to X servers.
For servers of graphic applications, it is an advantageous feature.
It is also easy to emulate RPC and a web server for MCP \cite{iamc} 
on our OpenXM stackmachines.