What is "id"?

In Chapter 5, the template for the Get factory method for an editable root collection is as follows:

public static EditableRootList GetEditableRootList(int id)
{
  return DataPortal.Fetch<EditableRootList>(
          new SingleCriteria<EditableRootList, int>(id));
}

Am I correct that the "id" argument would be used to fetch a distinct EditableRootList, which is somehow persisted in the data layer?  If the editable root list in my application always contains all root objects, would I do something like this:

public static EditableRootList GetEditableRootList()
{
  return DataPortal.Fetch<EditableRootList>();
}

...with the appropriate matching implementation of EditableRootList.DataPortal_Fetch?

thanks,

Frazer