QVT — Logging textual messages that depend on variables

He current representation of LogExp does not allow output
messages that are variable dependent. This is not realistic.
We should use here ordinary argument representation to encode
The text of the message and the level.

Suggestion: LogExp defined as a subclass of OperationCallExp.
The 'text', 'level' and 'element' fields can therefore be removed
since encoded as positional arguments.

RESOLUTION
(1) In Section 8.2.2.18 (LogExp) before "A log expression returns null"
adds the following paragraph.
"A log expression is a kind of operation call expression where the
first argument contains the message to be print, the second argument
gives the model element to be print (using an implict call to the 'who'
operation from the QVT Standard Library) , and the third argument gives
a level number for the log.
Only the first argument is mandatory.
(1) In Section 8.2.2.18 (LogExp) change the superclasses list
by replacing 'ImperativeExpression' by 'OperationCallExp'.
(2) In Section 8.2.2.18, remove the properties 'text', 'level'
and 'element'
(3) In Figure 8.6, change the inheritance of LogExp to OperationCallExp,
remove 'text' and 'level' attributes and remove 'element' link.