Complex sentence: An academic goal at that time was to work towards some fully automated tool whose inputs were a grammar plus a concise semantics description plus a concise target machine description, and whose output was a ready-to-use complete compiler.
Split into simpler sentences: An academic goal at that time was to work towards some fully automated tool whose inputs were a grammar plus a concise semantics description plus a concise target machine description. The tool's output was a ready-to-use complete compiler.