class RdfEngine implements Engine {

    @Override
    public void storeGroup(Group group) {
        Value title = group.getProperty(vf.createIRI(DCTERMS.TITLE.stringValue())).orElseThrow(() ->
                new IllegalArgumentException("Group must have a title"));
        if (resourceExists(group.getResource()) || groupExists(title.stringValue())) {
            throw new IllegalArgumentException("Group with that id already exists");
        }

        try (RepositoryConnection conn = repository.getConnection()) {
            conn.add(group.getModel(), context);
        }
    }

}