The first five fields pid, oid, mtype, mtag, msize are
primitive attributes of an event. But Ariadne allows the user to
add attributes to communication events in an effort to capture
state information. One can, for instance, add the values of variables
x and y at the local thread every time a message is received.
The user can inform Ariadne about this, by specifying
add fields int x, y to R;which adds the new attributes x and y to each R event. The syntax is
add fields <type> <attr-list> to <event-list>;
Also, the message tags related to each message vary from program to
program. So the user needs to tell Ariadne, what message tags to
expect. This can be done with
add utag <tag-name> to <event-list>;