Most people are familiar with searching a database and most people are also familiar with searching a search engine, but because the latter was not always the case before the web, these two products are usually so different at their core that combining the two either makes searches slow or highly structured searches impossible.
Metadata is difficult to infer, but if it is inserted at the point of publishing, as weblog style tools potentially allow, then to search the web like a database will require a product like Cerisent’s. There are other similar products from people like Software AG, but Cerisent’s is the only one where the core is written at a low enough level to scale to the requirements of a hybrid database/search engine.