Cortana is now saying "Hello World" as Microsoft officially introduces it as its digital assistant in response to Apple's Siri and Google Now. Redmond seeks to make the Windows Phone OS a strong rival to Android and iOS.

Corporate Vice President Joe Belfiore of the Windows Phone Group presented Cortana during a demonstration. He shows how the digital assistant respond to various voice commands, including Web information requests as well as how she follows instructions to carry out calendar tasks.

In his opening keynote at Microsoft's Build Conference in San Francisco on Wednesday, Belfiore said Cortana is a "truly personal digital assistant."

Cortana comes in beta with Windows Phone 8.1, the most recent version of Redmond's operating system for smartphones. Bing search engine powers the digital assistant, and Cortana completely replaces the current search function on Windows Phone, said Belfiore.

Users are in control of their relationship with Cortana. They can present her with a wide range of available information so she can use it to make personalized suggestions and recommendations for various situations.

Belfiore demonstrated how to "tell" Cortana to make a phone call, edit or add calendar entries, log reminders, display flight details, set alarms as well as interact and launch third party applications such as Hulu and Facebook.

For example, Cortana can be told to find the best Mexican restaurants in a specific city. Cortana does it by tapping on Yelp ratings and reviews, shortlist the search results to those which take reservations and call one of them.

According to Belfiore, Application Programming Interfaces (APIs) will let developers build applications for Cortana.

Cortana is very attractive and interesting, considering her capability to recognize voice. Users can interact with Mirosoft's digital assistant through text queries as well.