2 April 2014
Last updated at 19:44
By Leo Kelion Technology desk editor
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Microsoft's Joe Belfiore shows off one of Cortana's distinctive features
Microsoft has unveiled a virtual assistant for Windows Phone handsets.
The voice-controlled app, named Cortana, uses both the firm's search engine Bing and data stored on the handsets to make personalised recommendations and carry out tasks.
Apple and Google already offer comparable facilities on their iOS and Android platforms.
But one artificial intelligence expert said Microsoft's decision to wait until now to launch could prove wise.
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Amusing AI
It is no secret that many people's most enjoyable experiences with Siri have been discovering some of the funny responses built into the service by Apple.
So, it should come as no surprise that Microsoft has given its own virtual assistant a sense of humour.
Examples on show at the Build demonstration included its reply to being asked if it liked its name.
"I love it - it's certainly more catchy than Microsoft Personal Assistant V1 2014," the app said.
When asked what it thought of its animated circular logo, it told the Windows Phone chief that it thought it resembled "a hula hoop, a doughnut... and a halo," - a nod towards the video game that inspired its name.
But when asked to reveal the secret plot of the next game in the Halo series, Cortana objected.
"I'm quite certain that you don't have the proper security clearance for that information," it retorted.
It closed the event with another reference to the game, asking Microsoft's new CEO Satya Nadella when he planned to upgrade his title to "master chief executive".
"Siri and Google Now have a limited ability to extract the actual meaning from the words that somebody speaks," explained Prof Steve Young, professor of information engineering at the University of Cambridge.
"So, if you ask about things that Siri, for example, knows about like restaurants or baseball games, it works pretty well.
"But if you ask it about something that it's not been previously programmed to understand it simply passes the word into a search engine.
"I understand that for Cortana Microsoft has done a lot of work to automatically learn a much wider range of semantics... so the expectation is that it will be able to understand a good deal more."
The female-voiced Cortana - named after the AI system in the firm's Halo video game franchise - was unveiled by Windows Phone chief Joe Belfiore at the firm's Build developers conference in San Francisco.
It will initially be made available in the US, then next the UK and China and finally other markets as part of a wider Windows Phone 8.1 system software update.
Anticipatory app Cortana replaces the earlier search function on smartphones running Microsoft's operating system.
When launched from a pulsating button on the handset's start screen, it initially offers its own suggestion for the task the owner might want to carry out based on their location and past behaviour.
It can then be asked to do this or instead instructed to find other information, schedule appointments, set reminders or make other apps carry out the person's command.
If the user allows the software to access their calendar, email, contacts and browsing history the app will try to anticipate their needs.
For instance it can offer to schedule a flight if it spots a message received from a travel booking service, and flag news articles it thinks the user will be interested in.
However, if some of the inferences it makes are wrong the user can enter a "notebook" function to amend the rules it follows.
"The point is the user is in control of his or her relationship with Cortana," Mr Belfiore explained.
Launch glitches The notebook function can also be used to tweak Cortana's deductions of which friends and family are members of the owner's "inner circle" and when the owner's "quiet hours" are.
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New Nokias
Microsoft's takeover of Nokia's smart device business has yet to be completed, but Stephen Elop - the unit's chief - was still given substantial stage time at Build.
He announced what was described as a new flagship phone - the Lumia 930.
It features a 20 megapixel camera, a 5in (12.7cm) screen, wireless charging and four microphones to deliver "rich recording".
He also revealed a cheaper Lumia 630 model capable of supporting two Sim cards - a feature popular in India and China.
The takeover of Nokia's mobile unit is supposed to help Microsoft drive demand for the Windows Phone platform.
According to research firm IDC, the operating system only accounted for 2% of global smartphone shipments in 2013.
IDC believes the US firm will only make significant headway if it gets better at attracting consumers' interest.
"If you ask most users what they think, they have no idea what applications are available," said mobile devices analyst Francisco Jeronimo.
"Microsoft's biggest challenge now is marketing.
"Windows Phone is very competitive in terms of features when compared to iOS and Android. The firm just has to show that to end-users."
This is useful because the app can be made to limit who can reach the user during the prescribed time, requiring those who are determined not to be close friends or family to leave a message.
Mr Belfiore also carried out a demonstration showing how Cortana could be told to remind him to ask his sister about her new dog the next time they spoke. He explained an alert would then appear the next time they communicated by voice, text or email.
He also showed how the software could interact with specially adapted third-party apps. A request to see what a person had been up to saw Cortana launch Facebook and bring up the relevant friend's activity timeline.
But other parts of the presentation went less smoothly. The app repeatedly failed to convert the weather forecast from Celsius to Kelvin, and also misunderstood a request to make a phone call.
For situations such as this, Mr Belfiore noted that instructions could be typed rather than spoken.
He added that thanks to machine learning, the more people who interacted with Cortana the better it should get.
But one company watcher was concerned by what he saw.
"It has to be better than the competition for people to want to switch," said Lawrence Lundy, a tech specialist at the consultancy Frost and Sullivan.
"Siri and Google Now are going to get better as more people continue to use those services. My fear is that the Windows Phone user-base isn't as big, so it won't advance as quickly.
"Certainly it's not a good enough product to make people want to move to Windows Phone at this stage."
Other announcements at the event included news that Microsoft will not require manufacturers to pay a licence fee to install Windows 8 and Windows Phone on devices featuring screens smaller than 9in (22.9cm), which could help them compete against the rise of Google's operating systems.
It also confirmed that the forthcoming Windows 8.1 update would be offered as a free upgrade from 8 April. It features user interface changes including the ability to access the system's taskbar from any screen.
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