Computer Science

SQL has a number of additional features that we have not described in this chapter but that we discuss elsewhere in the book. These are as follows: we will present the following additional SQL features: various techniques for specifying complex retrieval queries, including nested queries, aggregate functions, grouping, joined tables, outer joins, and recursive queries;

In SQL, three commands can be used to modify the database: INSERT, DELETE, and UPDATE. We discuss each of these in turn. The INSERT Command In its simplest form, INSERT is used to add a single tuple to a relation. We must specify the relation name and a list of values for the tuple. The

Several criteria are normally used to classify DBMSs. The first is the data model on which the DBMS is based. The main data model used in many current commercial DBMSs is the relational data model. The object data model has been implemented in some commercial systems but has not had widespread use. Many legacy applications

Centralized DBMSs Architecture Architectures for DBMSs have followed trends similar to those for general computer system architectures. Earlier architectures used mainframe computers to provide the main processing for all system functions, including user application programs and user interface programs, as well as all the DBMS functionality. The reason was that most users accessed such systems

A DBMS is a complex software system. In this section we discuss the types of software components that constitute a DBMS and the types of computer database system software with which the DBMS interacts. DBMS Component Modules Figure illustrates, in a simplified form, the typical DBMS components. The figure is divided into two parts. The