Design of validation for the cfg PSet for the MessageService
	---------------------------------------------------------

The following errors in configuring the message service 
should be detected and reported rather than  proceeding
with a job, because the mysterious behavior they cause
is too tough to track down by hand:

At the main level, only the following PSets are allowed:
  A destination, as listed in the vstring destinations 
  A category, as listed in the vstring categories or messageIDs
  One of the following keywords, which are valid as PSets at the main level
	default  
	Note:  The meaning of default as a PSet at the main level is that
	of a DESTINATION PSet, not a category PSet.  However, for the 
	default desitnation, 

At the main level, only the following vstrings are allowed:
    categories		vstring
    messageIDs		vstring
    fwkJobReports	vstring
    destinations	vstring
    statistics		vstring

    The following are errors:
    In the destinations vstring, duplicate names.
    In the statistics vstring, duplicate names. 
    In the fwkJobReports vstring, duplicate names.
    In the categories vstring, duplicate names or names matching one of the
    destinations or statistics or fwkJobReports or a keyword.  
    Any destination or category is used as anything other than a PSet

    debugModules	vstring
    suppressInfo     	vstring
    suppressFwkInfo    vstring
    suppressDebug    	vstring
    suppressWarning	vstring

    The following are errors:
    Use of wildcards with suppressInfo or suppressWarning or suppressDebug.
    suppressDebug unless debugModules = "*"
    More than one debugModules if one is "*"
    

At the main level, only the following non-PSets non-vstrings are allowed:
    messageSummaryToJobReport    		bool
    generate_preconfiguration_message		string
    threshold					string	only certain values
    
Within a destination PSet, only the following PSets are allowed:
  A category, as listed in the vstring categories or messageIDs
  One of the following keywords, which are valid as PSets at this level
	default  
    	ERROR
    	WARNING
   	INFO
    	DEBUG
 
Within a destination PSet, only the following non-PSets are allowed:
    placeholder		bool	forbids others (because it will just return)!
    threshold		string	only certain values
    noLineBreaks	bool
    lineLength   	int
    noTimeStamps	bool
    output		string
    filename		string
    extension		string

Within a default PSet at the main level (which behaves much like a destination
PSet), only the following PSets are allowed:
  A category, as listed in the vstring categories or messageIDs
  One of the following keywords, which are valid as PSets at this level
   	ERROR
    	WARNING
   	INFO
    	DEBUG
	(Note that default is NOT present here)
  	 
Within a default PSet at the main level, only the following non-PSets are 
allowed:
    placeholder		bool	forbids others (because it will just return)!
    threshold		string	only certain values
    noLineBreaks	bool
    lineLength   	int
    noTimeStamps	bool
  And the following, which stem from being able to establish defaults 
  for categories: 
    limit		int
    reportEvery		int
    timespan		int

Within a statistics PSet, only the following (all non-PSets) are allowed:
    placeholder		bool
    output		string
    filename		string
    extension		string
    reset		bool
    
Within the fwkJobReport PSet only the following non-PSets are allowed:
    placeholder		bool
    output		string
    filename		string
    extension		string


Within a severity PSet, whether or not it is in the main or nested in a 
destination PSet,only the following are allowed:
    limit		int
    reportEvery		int
    timespan		int
    threshold	        int
    
Within a category PSet, whether or not this is the default category PSet,
and whether or not it is in the main or nested in a destination PSet,  
only the following are allowed:
    limit		int
    reportEvery		int
    timespan		int


Not allowed:

Use of filename or extension of cerr or cout.  (But output can be cerr or cout.)

In the destinations vstring, duplicate names.

In the statistics vstring, duplicate names, or cerr when destinations has
cout or vice-versa. 

In the fwkJobReports vstring, duplicate names.

In the categories vstring, duplicate names or names matching one of the
destinations or statistics or a keyword.  

Any destination or category is used as anything other than a PSet

Use of wildcards with suppressInfo or suppressWarning or suppressDebug not
allowed.

Anything tracked is not allowed.

The following is strongly discouraged unless the intent is to redirect
cout and cerr into different files:
	In the destinations vstring, presence of both cerr and cout.
However, this is NOT flagged as a flaw because it can be legit.





==========================================================================

Where does this validation get done?

Don't want all the modules to have been created (significant work into the job)
but do want the services, particularly Message service and Job Report, to have
started.

Partial Answer:  The validation should be done before or during
preModuleConstruction and preSourceConstruction, which should 
(possibly issue a message and) throw if there is a problem.

However, the PSet supplied to the ctor is no longer trivially available at
that point.  Although it could be saved, there would be potential snags:
* Saving by reference suffers a tiny risk of the PSet goign away.
* Saving by copying begs the question of what can and can't be asked of a copy.
* Saving the PSet ID should be airtight, but it may be a bit convoluted 
  (according to jbk) to re-obtain the PSet from the ID.

The solution is to do the validation -- and store the results -- in the
MessageService::MessageLogger ctor.  But we don't throw in that ctor, because 
that would squelch operation of the logger, which assumedly is "good enough"
despite the unintended behavior due to errors in the configuration.
Instead, we **check** the result in preModuleConstruction or 
preSourceConstruction, whichever happens first.

============================================================================

Working with a PSet:

The following (in addition to getParameter and getUntrackedParameter<T>) are 
potentially useful for validation:

    template <typename T>
    std::vector<std::string> getParameterNamesForType(bool trackiness = 
						      true) const ;
    ParameterSet trackedPart() const;
    bool empty() const;
    
    (the above two in tandem give us a way to check that everything is
    untracked)
						      

    // Return the names of all parameters of type ParameterSet,
    // pushing the names into the argument 'output'. Return the number
    // of names pushed into the vector. If 'trackiness' is true, we
    // return tracked parameters; if 'trackiness' is false, w return
    // untracked parameters.
    size_t getParameterSetNames(std::vector<std::string>& output,
				bool trackiness = true) const;
						      


    /// checks if a parameter exists
    bool exists(std::string const& parameterName) const;

    /// checks if a parameter exists as a given type
    template <typename T>
    bool existsAs(std::string const& parameterName, bool trackiness=true) const {
       std::vector<std::string> names = getParameterNamesForType<T>(trackiness);
       return std::find(names.begin(), names.end(), parameterName) != names.end();
    }




============================================================================

Code plan:

Each type of PSet and collection can be validated separately.  So for
example, we have validateDestinationPSet().  And the various overall lists
can be validated in context of the other lists.

We ask whether a parameter exists as the expected type before looking at 
its value; that way, we can see if it is there but with the wrong type.