This is a sample model for the sample Ziggy pipeline. 

It's a plain text file.

A model can be anything: an ASCII file, a binary file, even a directory! The main thing
about it is that, unlike data files, all versions of every model file are kept forever,
and never get overwritten. 

So how does that work? More to the point, how is it that this "model" can get read in
over and over again and never get overwritten, even though it's got the same file name
each time?

The way it works is that every time a given model gets read into the datastore, the 
resulting model file gets a version number and an import date appended to the file name.
When the model is staged out to the task directories, the version number and import date
are stripped off. In this way, we can manage different versions of a model that all have
the same name and never have a problem!

In some cases, though, the project may decide that a model is going to have a version
number and/or version date in the filename. So for example, this file could have been
called "sample-model-version-1-20220830.txt", and there's a way to define the model 
name convention such that Ziggy knows that the version number and the datestamp 
occur at specific points in the file name: specifically, define the model data type in
pt-sample.xml as follows:

<modelType type="versioned model" 
           fileNameRegex="sample-model-version-([0-9]+)-([0-9]+).txt"
           versionNumberGroup="1" timestampGroup="2" />

This tells Ziggy that the first regex group should be used as the version number and the
second should be used as the timestamp. 

A big advantage of including the version number and version date in the filename is that
if you do that, Ziggy can tell if you're reimporting a model that's already in the datastore,
and prevent you from doing that. It also prevents you from taking a new model, giving it
the model ID of the old model, and then importing that (which would cause the old model
to get deleted, and we don't want that). Without that information, Ziggy will allow you
to import the same model as many times as you like, and Ziggy will dutifully put a new
version number and date on it and keep it forever. 

The reason I didn't put a version number and version date into this model's name is that
I wanted you, the user, to be able to run data receipt over and over again without any
errors! If the model has a version number, then the 2nd time you try to import it, you'll
get an error.
