The NCAR Text And Graphics System is a graphics and text batch output production facility. It is distributed across several networked computers which run the UNIX operating system. The control function of TAGS is implemented as multiple processes which communicate via message passing. The TAGS message passing scheme allows processes to exchange a simple form of associative memory, called a parcel, in an architecture neutral fashion. The associative memory is implemented as a binary tree containing pairs of keyword and value strings ordered by collating sequence. The underlying interprocess communication mechanism is based on Berkeley internet stream sockets. This message passing scheme provides information hiding inside the message, and allows new parameters to be added to messages without recompiling or relinking intermediate modules which handle the messages. The software as described is available from NCAR via anonymous FTP at no cost under a noncommercial license.
