Oracle CEO Larry Ellison Asa Mathat | All Things Digital When HP and Oracle were fighting in court last summer over HP's Itanium servers, HP hinted it would come after Oracle for $4 billion.

HP won the suit and is back in court, to hear what damages, if any, it is entitled to get. Sure enough, HP is aiming for $4 billion.

It put an expert witness on the stand who said Oracle cost HP $4 billion to $4.2 billion in business.

The suit concerned Oracle's plans to stop making its flagship database software for HP's high-end, expensive Itanium servers. A California judge ruled in HP's favor and said that Oracle had to continue to make its database products for Itanium.

In a hearing in a Santa Clara, Calif. court today, HP's had an economist testify. He said that the uncertainty caused by Oracle's decision drove customers away, reports IDG News Services' Stephen Lawson.

In the second quarter of HP's 2011 fiscal year, when the fight began, Itanium revenue fell 11 percent from the year prior, HP's expert witness said. The following quarters it fell 18.1 percent, 32 percent and 38 percent from the year-ago quarters.

Oracle's lawyers had a pretty good counter-argument for the falling revenue. They pointed out that during that time HP was undergoing a lot of turmoil, including firing its CEO Leo Apotheker.

Both HP and Oracle declined comment.