Complex sentence: Geordi realizes that when he asked the computer to create the program he had asked for an adversary who could defeat "Data", not Sherlock Holmes; as a result, the computer gave the Holodeck character Professor Moriarty the knowledge and sentience needed to challenge Data.
Split into simpler sentences: Geordi realizes that when he asked the computer to create the program he had asked for an adversary that could defeat "Data", not Sherlock Holmes. As a result, the computer gave the Holodeck character Professor Moriarty the knowledge and sentience needed to challenge Data.