The number of major database management system products continues to shrink according to Meta Demand Research, a major market research firm. Four products now account for 83 percent of all sales. The clear leader is Oracle with a 44 percent market share. The other major products in order of market share are Sybase (22 percent), Informix (10 percent), and DB2 (7 percent). Oracle's dominant position is in large part due to the fact that it provides support worldwide-something which is increasingly important as application software vendors seek to sell globally.
There are relicensing costs involved when an application software vendor changes from one database management system to another. Libraries should seek to protect themselves from extra costs by stipulating in their contracts .that a vendor's decision to change from one database management system to another shall not result in a financial obligation to the library beyond the regular software maintenance/enhancement charges identified in the contract.