TABLE OF CONTENTS A database system is composed of much more than just the data definition language, data manipulation language, and data control language. These simply represent the interface into the actual database system. The core of a database management system is the collection of services that provide the persistence of data in the database and the functionality to guarantee the consistency and correctness of data and the adherence to ACID properties by transactions (Figure 2.30). The ACID properties include the atomic, consistent, independent, and durable execution of a transaction on the database. We will discuss these in more detail later in this chapter.
The architecture of a database system is comprised of a set of services built on top of basic operating system services, system file storage services, and primary memory buffer management services. The file manager is the database's interface to the persistent stored information. The information managed for the database by the file system includes the internal, conceptual, and external schema for the stored information (metadatabase); the actual database; and the database log file. The log files include before images (buffer values), after images, redo records (actions of committed transactions), undo records (actions of uncommitted transactions), commit records, abort records, and transaction begin records.
Through the basic features of process management, interprocess communications, synchronization, buffer management, and file management the database systems services can be constructed. These services include catalog management, integrity management, transaction management,...
