David Swatland, captain in the U.S. Coast Guard for the San Francisco Bay region, looked puzzled and dismayed by a simple question at the Stanford University symposium Wednesday, "The Search For Jim Gray."

He had been asked by one of the 23 attendees in the audience, "So what do you think happened to him, most likely?" meaning what was the logical explanation of how a noted Microsoft computer researcher and experienced sailor disappeared on his boat Jan. 28, 2007.

Swatland hesitated, then said: "I can't answer that." The Coast Guard never recovered any debris or spotted any sign of his bright-red-hulled boat with its black mast and the name "Tenacious" in bold white letters on the side, he said. It had been one of the most intensive searches ever mounted off the San Francisco coast, he added.

What's more, Gray's wife, Donna Carnes, and family, after the search of the ocean's surface ended, quickly mounted a survey of 300 square miles of the seafloor between the Golden Gate and the Farallons, extending out to the most likely places that Gray's boat might have reached. This search also turned up nothing, even though the side scanning sonar was able to draw a map of rocks and sand bars on the ocean's floor.

Overlapping sweeps were done until each part of the seafloor was inspected twice. Man-made objects, including both previously known and unknown wrecks, were easily spotted. In some cases, an underwater robot video camera was sent to the seafloor to inspect them. None was the Tenacious.

The two searches, one above the water, one below, turned up no evidence of Gray, and Swatland would not explain the inexplicable. Gray's disappearance has left his friends and family with a painful, "ambiguous loss," with no answers and no certainty as to what happened to him, other than to know everything humanly possible had been done to find him.

That's one reason why on Saturday, the family, the Association For Computing Machinery, and the University of California at Berkeley are staging an event in his honor. One of the topics will be dealing with ambiguous loss by an expert on the subject, Pauline Boss.

And that's why Mike Olson, lead organizer in Tenacious Search, the effort by friends and associates to use satellite and aerial photographic imagery to locate the missing boat, said of Saturday's event: "It's a tribute, not a memorial" or a funeral.

Olson, a friend of the family and former CEO of Sleepycat Software, tried to address another ambiguity, an outsider's question raised in some articles on Gray's disappearance. "I don't believe he did a rabbit -- ran away. That's horse---!" said Olson at the conclusion of the symposium. "I believe Jim was lost at sea. He had a bad three minutes" where an accident of unexplained origin damaged his boat and he couldn't cope with it fast enough.

At Saturday's tribute, Olson will describe how Gray's friends mounted their "amateur search" after the Coast Guard had flown search planes and put patrol vessels on the water to execute organized search patterns.

One of Gray's colleagues, Michael Stonebraker, the former Berkeley professor of computer science who was developing the Ingres database system as Gray worked on IBM's System R, will speak on "Why Did Jim Gray Win the Turing Award?"

“He was the ideal researcher. He knew an enormous amount. And he spent a lot of time figuring out what others were doing and cross fertilizing that knowledge. He was known and loved by a huge number of people,” said Stonebraker in an interview.

"Jim was the reason I joined IBM," recalls Pat Selinger, the member of the IBM DB2 team who came up with the method for optimizing SQL queries to relational databases. "On my interview day, Jim was part of the interviewing team, and we got to talking about operating system concurrency and transaction processing. I loved it. I had a lot of fun at that interview. I thought, 'Wow. I could go to work here and get paid to do this every day.' "

Don Haderle, IBM DB2’s chief architect and sometimes referred to as the father of DB2, said Gray "was a magnet. He was attractive and drew people to him in a social way. Twenty years ago, every researcher wanted to tell you why his idea was better than the one you had just heard about. Jim [instead] listened to you. He was interested in your perspective. He pulled the positive out of what you had to say."

Gray eventually moved on from IBM to other positions in the computer industry at a time when IBM tried to closely guard its lab work as intellectual property. "When Jim left IBM, he was still interested in what you were doing. Everybody told Jim everything. He got insider knowledge without trying," Haderle said with a chuckle. Said Selinger: "Jim was an awesome team member. He brought out great ideas from everybody, then he had the ability to articulate things crisply and clearly. He pulled together what others were saying to tell a story."

The tribute at the UC Berkeley campus is scheduled for 9 to 10:30 a.m. Saturday at Zellerbach Hall.

Editor's Note: This story was updated June 24 to change several references from System R to DB2 to better describe people's past work at IBM.