The chiefs of Google and Oracle were served up to jurors on Tuesday as opening witnesses in a patent case aimed at Android software used to power smartphones and tablet computers.

Oracle is accusing Google of infringing on Java computer programming language patents Oracle obtained when it bought Java inventor Sun Microsystems in a $7.4 billion deal brokered in 2009.

Google has denied the patent infringement claims and said it believes mobile phone makers and other users of its open-source Android operating system are entitled to use the Java technology in dispute.

Google unveiled the free Android operating system two years before Oracle bought Sun.

Opposing attorneys laid out their stances for jurors after the trial got under way on Monday in a federal courtroom in San Francisco, then Google co-founder and chief executive Larry Page was called to testify.

Page appeared in the form of a video recording of him being grilled by a powerhouse attorney from Oracle's legal team, according to reports filed from the courtroom.

Page's testimony was followed by Oracle chief Larry Ellison fielding questions on the witness stand.

Page was challenged on evidence showing that the Android team had sent word up the chain-of-command that Google should get a license from Sun to use snippets of Java in the smartphone platform.

Google has held firm that such a deal was not necessary since Android used only portions of Java code that were publicly available.

US District Court Judge William Alsup has allocated eight weeks for the trial, which he dubbed on opening day as "The World Series of IP."

Early this month, Oracle spurned a proposal that Google pay about $3 million in damages and potentially cut the company in for less than a percent of Android revenue.

Northern California-based business software titan Oracle rejected the offer as too low.

Google has maintained that Sun, before it was acquired by Oracle, had declared that Java would be open-source, allowing any software developer to use it, and released some of its source code in 2006 and 2007.

Oracle completed its acquisition of Sun, a one-time Silicon Valley star, in January of 2010 and subsequently filed suit against Google.

Oracle lawyers in opening remarks accused Google of profiting from its intellectual property (IP). Google attorneys fired back that Oracle was using its purchase of Sun to cash-in on the popular Android mobile platform.

Google-backed Android software is used in an array of devices that have been gaining ground in the hotly competitive global smartphone and tablet markets.