HP sued Oracle for breach of contract last year after the database giant announced in March that it would stop developing new versions of its future products for the Itanium processor. Itanium powers HP's so-called Business Critical Systems hardware for highly demanding enterprise applications, but Oracle says the chip line is reaching the end of its life.

On Monday, the companies' lawyers faced off before Judge James Kleinberg in Santa Clara County Superior Court. Oracle co-President Safra Catz and HP board member and former enterprise business chief Ann Livermore, the main negotiators of that agreement, looked on in the courtroom. Livermore was set to testify later Monday. In the first phase of the trial, Kleinberg, without a jury, is to rule on whether the two companies had a valid contract.

HP's attorney, Jeff Thomas, focused in on the wording of the so-called Hurd Agreement, in which the companies reaffirmed their longstanding business partnership after Oracle hired former HP CEO Mark Hurd and HP sued Hurd for breaching a confidentiality agreement. Both he and Oracle's lead attorney focused in on a paragraph of the agreement that said Oracle would "continue to offer its product suite on HP platforms ... in a manner consistent with the partnership as it existed prior to Oracle's hiring of Hurd."

That clearly means Oracle has to keep porting its database, middleware and other key software the HP's HP/UX version of Unix for its Itanium-based Integrity servers, Thomas said.

"The language of the contract itself is perfectly consistent with HP's interpretation," Thomas said. "It cannot remotely be squared with Oracle's interpretation."