6. (15) It is possible that the program might connect to different databases, but communicating with more than one could be problematic. So, we want to enforce that only one database can be used during the lifetime of the program. Subsequent requests for database algorithms will receive the original database. a. Name the pattern b. Show a sample implementation (pseudo code and UML diagram) c. In one sentence, describe a secondary property of this pattern, and why it is desirable