For this application, we will consider IBM DB2 catalog data (i.e., metadata) for IBM's enterprise-class servers running the z/OS (formerly OS/390 or MVS) operating system. One of the outcomes of this question is to give you some experience in actually exploring the contents of what's in an RDBMS catalog. This will also give us a head start in thinking about query optimization-a major part of this course.
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In this course, we will frequently encounter a program that is a crucial component of an RDBMS. That program is called an optimizer. It tries to determine the optimal access path when accessing (e.g., retrieving) data in a database. An optimizer obtains statistics or metadata (i.e., data about data) from a data repository in the DBMS called a catalog. The catalog will have information about the columns of tables and indices; the number of rows in a table; the numbers, types, and (possibly) distribution of values for columns in the tables; and literally hundreds of other pieces of information.