After the model is designed (refer to the spiral 4 of the Travel Impression Model figure) and its code is generated, the model will be initialized with some basic data starting with its entries. This is done in the lib/travel/impressions/init.dart file:

initTravelImpressions(var entries) {
  _initCountries(entries);
  _initTravelers(entries);
}

We will start by creating a country and some of its places, together with the web links, from the entries parameter:

_initCountries(var entries) {
  var countries = entries.countries;
  var country = new Country(countries.concept);
  country.code = 'BA';
  country.name = 'Bosnia and Herzegovina';
  countries.add(country);

In the Country concept of the graphical model, there is no code attribute of the String type. The code attribute is inherited from dartling. In a concept, you do not need to use the inherited code attribute. However, if you use it, its values must be unique. Note that a new country...