Yahoo is opening up its search engine vault and letting third parties develop customized Web searches using its own technology. Build your Own Search Service (BOSS) encourages start-ups, Web developers and anyone else to build and launch Web-scale search products that take advantage of the Yahoo Search index. Yahoo is giving the keys to its crawling and indexing capabilities along with ranking and relevancy algorithms to developers in the hopes to increase its own search market share while encouraging the next step in search engine functionality.