boolean downgrade = checkWebServerVersion();
    if (! downgrade) return; // we are ok

    Set<IInstallableUnit> toUninstall = getDowngradeFeatures();
    // assume toUninstall has "test.feature.feature.group 2.0.0"

    if (toUninstall.size() > 0) {
        UninstallOperation op = new UninstallOperation(session, toUninstall);
        IStatus result = op.resolveModal(monitor);
        if (result.isOK()) {
            op.getProvisioningJob(monitor).runModal(monitor);
    }