A physical subtree structure is very similar to a top-level experiment tree. It is contained in .TREE, .DATAFILE and .CHARACTERISTICS files in the file-system, and it may have physical subtrees of its own.
The physical subtree is known to MDSplus via the logical name (subtree)$DATA, just as the top-level tree is known by (experiment-name)$DATA, i.e. CMOD$DATA or NSTX$DATA. The 12-character node-name length limit carries over to the subtree name, since they must match. It is often convenient, but not necessary, to locate the files for the physical subtrees in a directory immediately below that for the files of the parent tree.
There are many I/O efficiency advantages to opening physical subtrees in order to read files, rather than opening the top-level tree and following a long path to read a node in a subtree. Whenever a tree is opened, all of its physical subtrees are also opened; so opening the lowest convenient subtree minimizes the number of files involved. It also saves a lot of typing.
To create a new physical subtree,
$CREATE/DIRECTORY DISKNAME:[OPERATIONS] or $CREATE/DIRECTORY DISKNAME:[EXPER.OPERATIONS] for experiment EXPER (i.e., CMOD)
$ DEFINE OPERATIONS$DATA DISKNAME:[OPERATIONS] or $ DEFINE OPERATIONS$DATA DISKNAME:[EXPER.OPERATIONS]
BIRCH$ tcl TCL> edit nstx TCL> add node .operations TCL> dir \NSTX::TOP :DEMO8210 :NEWPPLCC908 :PPLCC908 :PPLCCMEM :TESTDECODER :TST404 OPERATIONS Total of 7 nodes. TCL> set node .operations /subtree TCL> write TCL> exit
The nodes of the subtrees are not available when editing the upper-level tree. (They are not indicated at all.) To verify that the connection has been successful, open the higher-level tree for readonly (using SET TREE in TCL, or TRAVERSER in normal mode).