According to legal experts, the outcome will decide how patent laws protect exclusive technology. The Canadian company had taken the software giant to court in the US in 2007 over violations of its patent in Word applications and won the case and got $290 million in damages in December 2009.

In its lawsuit in a Texas court, i4i had claimed that the world's biggest software company infringed on a patent granted to it in 1998.

The patent pertained to i4i's technology that can open documents using the XML computer programming language and manipulate complex data in electronic documents The technology allows users to sort out and manage tons of information by turning complex documents into more accessible databases.

The Toronto company claimed that Microsoft violated its patent when it created Word 2003 and Word 2007 software. Later in 2009, the US court of appeals upheld the lower court order banning Microsoft from selling its patent-infringing Word processing software from January 11.

Microsoft complied with the court order by stopping selling versions of Word with the disputed technology from that date. In May last year, the Canadian company also got another boost when the US Patent and Trademark Office rejected Microsoft's request and confirmed that the belonged to i4i Inc.

But Microsoft challenged the verdict in the US supreme court in August last year, arguing that the current system is disproportionately loaded in favor of patent holders. In a case that that may fundamentally overhaul the US patent system, Microsoft is said to enjoy the backing of Google, Yahoo Inc., Apple and Intel Inc.

But the US administration, venture capitalists and patent inventors and some pharmaceutical companies have thrown their weight behind i4i. Pharmaceutical giants such as Bayer, Merck and Nexgen are i4i's clients.

Toronto-based i4i chairman Loudon Owen said Sunday that Microsoft has  "the right to keep appealing and that's what they're doing.'' But he added that the patent has no meaning "if it's not enforceable.''

The verdict is expected in the summer. If Microsoft loses, it will have to immediately pay $290 million in damages to the Toronto company.