Return dict with identifier/URL pairs for the dataset items.

def generate_item_urls(self):
        """Return dict with identifier/URL pairs for the dataset items."""
        item_urls = {}
        for i in self.dataset.identifiers:
            relpath = self.dataset.item_properties(i)["relpath"]
            url = self.generate_url("data/" + relpath)
            item_urls[i] = url
        return item_urls