*access
**
ACCESS MATRICES

In the filing machine version of the TRIPOS filing system each entry in a
directory for an object has an associated access matrix.  This appears to
be a string with four main parts - the V, X, Y, and Z parts respectively
separated by the slash character.  If you have V access to the entry you
will have the access given by the first part of the matrix, X access the
second, and so on.  Your access may, in fact, be represented by a combination
of the parts - if you have both X and Y access for example.

Whatever the object the entry refers to the appearance of the any of the
characters D,A,U have the following meaning.  They refer to the entry itself
rather than the object that it references.

                D - this entry can be deleted (i.e. DELETE will work!)
                A - the access matrix for this entry can be changed
                    (using the ALTER command)
                U - this entry can be updated (i.e. it can be deleted by
                    RENAMEing or ALIASing another file on top of it)
                    U ONLY APPLIES TO FILES

If the object refered to by the entry is a directory the appearance of any
of the characters C,F,V,X,Y,Z have these meainings:

        C - you may create new file or directiory entries in this directory
        F - you may create new file entries in this directory
        V - you have "V access" to all the entries in this directory
        X - you have "X access" to all the entries in this directory
        Y - you have "Y access" to all the entries in this directory
        Z - you have "Z access" to all the entries in this directory

Lastly if the object refered to by the entry is a file the characters E,R,W
mean:

                E - this file can be executed as a program
                R - you may read this file
                W - you may write to this file

In point of fact E access above is not checked anywhere and so is currently
meaningless on TRIPOS.  Another point of interest is the fact that the
filing system guarantees never to generate an object whose access matrix
does not include at least D or A access (since such objects could never be
removed from the filing system!).

The default access matrices, given to newly created entries, are:

        for FILES               /DAURW/ARW/RW/R
        for DIRECTORIES         /ACV/ACX/CY/Z

(The slashes "/" delimit the access given to those with V,X,Y and Z access
 respectively to the directory containing the entry).


