This documentation is not using the current rendering mechanism and is probably outdated. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
The model is based on an object representation of the iCal data format and relies heavily on TYPO3 services. At the top level is a parent class that defines many default fields and methods related to the iCal data format.
Sitting beneath this top level data model are the many concrete models that implement its data type. The only requirement on these models are that they map data into the required fields of the top level data model. How and where data storage occurs (in a database or otherwise) is the decision of the data model in question. While the top level data model may provide default functionality for common functionlity, the concrete models are in no way limited by this as they can always override methods from a parent class. In addition, concrete models may provide additional fields to augment the data model as well, so the parent class only serves as a starting point for shared functionality.