NEW YORK ( TheStreet) -- Google ( GOOG) bought a big seat in the local dining market.

The Net search giant says it has acquired restaurant review publisher Zagat for an undisclosed amount of money.

The move will give Google a popular guidebook franchise along with a big online dining discussion forum as it pushes further into the local advertising market.

"Zagat will be a cornerstone of our local offering," Google local business chief Marissa Mayer wrote in a blog post Thursday.

Zagat reviews feature a numerical rating as well as a composite opinion based on snippets of user surveys.

The move is a direct attack on upstarts, like review site Yelp, local coupon specialist Groupon and is a potential threat to restaurant reservation broker OpenTable ( OPEN). OpenTable shares fell 10% on news of the deal Thursday.

Google has been beefing up its local daily-deal effort with Google Offers and has been pushing its local search and location-based services on mobile devices as a way to capture more of the local advertising market.

Google shares were up 0.5% to $537 at midday Thursday.

--Written by Scott Moritz in New York.

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