258 CHAPTER 15: HIERARCHICAL DATABASE SYSTEMS (IMS) The IMS database management system as it exists today represents the evolution of the hierarchical database over many years of development and improvement. IMS is in use at a large number of business and government installations throughout the world. IMS is recognized for providing excellent performance for a wide variety of applications and for performing well with databases of moderate to very large volumes of data and transactions. 15.2.1 Data Language I Because they are implemented and accessed through the use of DL/I, IMS databases are sometimes referred to as DL/I databases. DL/I is a command- level language, not a database management system. DL/I is used in batch and online programs to access data stored in databases. Application programs use DL/I calls to request data. DL/I then uses system access methods, such as the Virtual Storage Access Method, to handle the physical transfer of data to and from the database. IMS databases are often referred to by the access method they are designed for, such as HDAM (Hierarchical Direct Access Method), HIDAM