OpenInsight file operation requests originate in BASIC+ commands such as READ, WRITE, DELETE, LOCK, UNLOCK, SELECT, READNEXT, or in System Monitor routines such as ATTACH_TABLE, DELETE_ROW and LIST_TABLES. Developers write these commands into their programs, or execute the routines from the System Monitor, to control the flow of data to and from the file.
When a program or routine executes, each file-oriented statement becomes a call to the filing system. For example, if an BASIC+ program encounters a READ statement, and the file being read is a Linear Hash file, OpenInsight generates a call to the program RTP57, the Linear Hash BFS, with the appropriate "read" code.
Because BASIC+ is independent of filing systems, the call arguments for filing system subroutines use a standard protocol. BASIC+ produces the same subroutine call for all filing systems, always using the same arguments.
A READ statement, for example, always produces the same BFS call, regardless of what filing system is actually being accessed by the read logic. By extension, all MFSs must use the same calling conventions.
