Data Management

DDMS Overview


Basic Elements

Data Objects


User Applications

Manipulating Data


Further Info

Data Management

Detailed Information About the JGOFS Distributed Database Management System (DDMS)


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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