Computer Associates Int'l, Inc. v. Altai, Inc. 982 F.2d 693 (2d Cir. 1992) CA wrote a computer program that would allow their scheduling software to run on different kinds of computers. Altai sold a similar kind of scheduling software, so they asked their programmers (who were kept segregated from CA's program), to write a program with the same functionality, which they did. CA sued Altai for copyright infringement. The Trial Court found for Altai. CA appealed. The Appellate Court affirmed. The Appellate Court looked to Baker v. Selden (101 U.S. 99 (1879)), and noted that an idea cannot be copyrighted, only the expression of that idea can be copyrighted. The Court applied the Abstraction - Filtration - Comparison test. In Abstraction the court breaks up the program into different levels, from very general to very specific. E.g. Main purpose, program structure, modules, algorithms, data structures, source code. In Filtration, the court decides what components are absolutely essential to fulfilling the abstract function of the program at the various levels. Also filter out everything that is dictated by efficiency, external factors, or in the public domain. In Comparison, the court looks at the components of the program which are not absolutely essential to fulfilling the abstract function of the program to see if they are similar. The Court performed the Abstraction - Filtration - Comparison test and found that the copyrightable elements from CA's program were not substantially similar to those elements in Altai's program. Basically, this case said that what the courts need to do is to sift out all elements of the allegedly infringed program which was ideas of dictated by efficiency or external factors, or taken from the public domain in order to find "a core of protectable expression." At that point the courts should focus on whether there are substantial similarities between any elements within this core in the two programs.