Overall System Structure

1. In most cases the operating system provides only the most basic services, and the database system must build on that base. A database system consists of a number of functional components, including:
   • File Manager - manages allocations on space on disk storage, and the storage structures used to represent information stored on disk.
   • Buffer Manager - manages the transfer of information between disk and main memory (MM).
   • Query Parser - translates query language statements into a lower-level language.
   • Strategy Selector - attempts to convert a user's request into an equivalent but more efficient form.
   • Authorization and Integrity Manager - tests for the satisfaction of integrity constraints (such as key constraints) and checks the authority of users to access data.
   • Recovery Manager - ensures that the database remains in a consistent (correct) state despite system failures.
   • Concurrency Controller - ensures that concurrent interactions with the database can proceed without conflict.
2. There are also several required data structures (see Figure 7.1).

    
   Figure 7.1:  System structure
   

   • Data Files - store the database itself.
   • Data Dictionary - stores information about the structure of the database, e.g. authorization information.
   • Indices - provide quick access to data with a particular value.
   • Statistical Data - information about data in database, used by strategy selector.