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Data Management
Detailed Information About the JGOFS Distributed Database Management System (DDMS)
Communications
There are two parts to the problem of communicating information from
the object on one machine to the application on another:
- The "physical" connection which involves setting up a data
transfer pathway between the two processes on the different machines.
To do this, the software uses NCSA's HTTPD
and a JGOFS data server program.
- The protocol for the communication which
ensures that the processes understand the requests and replies.
All exchanges between the user's application program (process
1) and
the method/ translator (process 2 -- perhaps on another machine) are
made via interprocess communications using "pipes" or "sockets" as
defined in Berkeley UNIX. In the case of a locally defined object, a
pipe is opened between the application and the method processes. For a
remotely defined object, the application opens a socket to the HTTP daemon on the other machine and starts the
server. The server effectively connects the
standard output stream on the method to the socket in the
application. The processes then begin exchanging information according
to the JGOFS protocol.
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