This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

He also invested in a shopping mall in Columbus, Ohio. He has talked about some of those who have helped him over the years in business: "I couldn't have learned about business without a parade of teachers guiding me... from Milton Friedman to Donald Trump... and now, Les Wexner and Warren Buffett. I even learned a thing or two from Planet Hollywood, such as when to get out! And I did!" He has significant ownership in Dimensional Fund Advisors, an investment firm. Schwarzenegger is also the owner of Arnold's Sports Festival, which he started in 1989 and is held annually in Columbus, Ohio. It is a festival that hosts thousands of international health and fitness professionals which has also expanded into a three-day expo. He also owns a movie production company called Oak Productions, Inc. and Fitness Publications, a joint publishing venture with Simon & Schuster.
What investment firm does Schwarzenegger maintain partial ownership of?