SAP AG, the largest business-management software maker, agreed to buy Ariba Inc. to add a cloud-computing applications maker in a transaction valued at about $4.3 billion.

SAP offered $45 a share for Ariba, whose board of directors has unanimously approved the deal, Walldorf, German-based SAP said in a statement Tuesday. The transaction will probably be completed in the third quarter subject to approval by Ariba shareholders and regulators, it said.

Ariba, based in Sunnyvale, California, is the leader in cloud-based collaborative commerce applications and the second-largest cloud vendor by revenue, SAP said. As the battle for on-demand software intensifies, SAP has stepped up the pace of acquisitions. It bought SuccessFactors Inc. in December 2011 for $3.4 billion, adding a maker of online personnel management applications to help it enter the cloud-computing market.