* written to log files or stored in the search index. Implementations include
 * search logs, click logs, favorite logs, and user information logs.
 */
public interface SearchLogEvent {
    /**
     * Gets the unique identifier for this search log event.
     *
     * @return The event ID
     */
    String getId();

    /**
     * Gets the version number for this search log event.

        // Create different implementations
        SearchLogEvent event1 = new TestSearchLogEvent("id1", 1L, "type1");
        SearchLogEvent event2 = new NullSearchLogEvent();
        SearchLogEvent event3 = new EmptySearchLogEvent();

        // Test polymorphic behavior
        SearchLogEvent[] events = { event1, event2, event3 };

        for (SearchLogEvent event : events) {

    *
    * @param searchLogEvent The search log event.
    * @return The source map.
    */
    protected Map<String, Object> toSource(final SearchLogEvent searchLogEvent) {
        final Map<String, Object> source = toLowerHyphen(searchLogEvent.toSource());
        source.put("_id", searchLogEvent.getId());
        // source.put("version_no", searchLogEvent.getVersionNo());