Computer software exports in 1997 tumbled to roughly half of the previous year's levels, due mainly to the Asian economic crisis, a joint survey released Monday by four industry associations in Japan and the U.S. indicated.Exports totaled 2.8 billion yen, while imports increased by 20.7 percent to hit 474.9 billion yen, the survey showed.About 80 percent, or 391.3 billion yen, of the imports were from the United States, it said. Of the U.S. imports, system software such as operating systems, database software and compilers accounted for 67.3 percent, the survey said.The annual survey was conducted by the Japan Electronic Industry Development Association, the Japan Information Service Industry Association, the Japan Personal Computer Software Association and the American Electronics Association.