SAN FRANCISCO — The panel was stuffed with mobile app heavyhitters including a former Google vice president and the architectof Trulia's popular mobile app.

Their mission was simple: Explain to the assembled audienceWednesday at the Open Mobile Summit the how-to of building acaptivating app that keeps users coming back.

And keep in mind a couple points. With smaller devices –smartphones and smaller – users most certainly want to minimizetheir own data input. Also, the smaller the device, the fewer pushnotifications and similar, welcome news to the typical user.

That is: what's acceptable on a 10-inch tablet might be wildlywrong on a connected wristwatch and, for the mobile app developer,these are facts that have to be digested.

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Another factor: ever more traffic is stampeding into mobile. AtTrulia, for instance, Steven Yarger said that the company's mobiletraffic three years ago was maybe five percent of total traffic.“Today it is nearing 50%.”

That's the norm. Mobile is emerging as the dominant platform,mainly because it is consumed on devices that we have with uswherever we go,

Mobile also is unique, said Vishal Sharma, the former Googlevice president who headed the Google Now initiative. “Location forsure is crucial with mobile. The device is with you at all times.What are you hoping to accomplish? Inferring intent becomescritical for the app developer, it's the most important thing.”

That is, what does this user appear to want to get out of thiscontact? Guess wrong and it may alienate the user. Keep guessingright and, probably, the user will keep coming back, suggested thepanelists.

Knowing what to base guesses on is becoming key. Raj Singh, CEOof Tempo Ali, an augmented calendar app, noted: “We used to believemore data is better. Not anymore. We have realized that there is an80/20 rule. Two or three data sources get us 95% of what we want.The next dozen don't move the needle.”

That means apps developers have to learn what matters and whatneeds to be ignored about this user, now.

“It's very complicated,” said Sharma. “If it appears to besimple you don't know to consume the data.” He added, “It will keepgetting more complicated.”

Last thought came from the panel's moderator, Ravi Mhatre, apartner at investment firm Lightspeed Ventures. Said Mhatre as thepanel neared its end, “I am hearing, to a person on the panel, thatthe bar has been raised. The right things have to show up inlimited real estate. There is great opportunity in mobile. But ifyou want people to use your app, the standards are quite high.”