How big is the World Wide Web? Many Internet engineers consider that query one of those imponderable philosophical questions, like how many angels can dance on the head of a pin.

But the question about the size of the Web came under intense debate last week after Yahoo announced at an Internet search engine conference in Santa Clara, California, that its search engine index - an accounting of the number of documents that can be located from its databases - had reached 19.2 billion.

Because the number was more than twice as large as the 8.1 billion documents currently reported by Google, Yahoo's fierce competitor and Silicon Valley neighbor, the announcement - actually a brief mention in a Yahoo company Web log - set off a spat.

Google questioned the way its rival was counting. Sergey Brin, one of the two co-founders of Google, suggested that the Yahoo index had been inflated with duplicate entries in such a way as to cut its effectiveness despite its size.

"The comprehensiveness of any search engine should be measured by real Web pages that can be returned in response to real search queries and verified to be unique," he said on Friday. "We report the total index size of Google based on this approach."

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