So far, we have discussed the characteristics of single relations. In a relational database, there will typically be many relations, and the tuples in those relations are usually related in various ways. The state of the whole database will correspond to the states of all its relations at a particular point in time. There are
Relational Model Constrains and Relational Database Schemas Read More »
The relational model represents the database as a collection of relations. Informally, each relation resembles a table of values or, to some extent, a flat file of records. It is called a flat file because each record has a simple linear or flat structure. For example, the database of files that was shown in Figure
Relational Model Concepts in DBMS Read More »
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
Classification of Database Management Systems Read More »
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
Centralized and Client/Server Architectures for DBMSs Read More »
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
The Database System Environment Read More »
Already we discussed the variety of users supported by a DBMS. The DBMS must provide appropriate languages and interfaces for each category of users. In this section we discuss the types of database languages and interfaces provided by a DBMS and the user categories targeted by each interface. DBMS Languages Once the design of a
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Three of the four important characteristics of the database approach, listed in Section, are (1) use of a catalog to store the database description (schema) so as to make it self describing, (2) insulation of programs and data (program data and program operation independence), and (3) support of multiple user views. In this section we
Three Schema Architecture and Data Independence Read More »
One fundamental characteristic of the database approach is that it provides some level of data abstraction. Data abstraction generally refers to the suppression of details of data organization and storage, and the highlighting of the essential features for an improved understanding of data. One of the main characteristics of the database approach is to support
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In spite of the advantages of using a DBMS, there are a few situations in which a DBMS may involve unnecessary overhead costs that would not be incurred in traditional file processing. The overhead costs of using a DBMS are due to the following: High initial investment in hardware, software, and training The generality that
When Not to Use a DBMS Read More »
We now give a brief historical overview of the applications that use DBMSs and how these applications provided the impetus for new types of database systems. Early Database Applications Using Hierarchical and Network Systems Many early database applications maintained records in large organizations such as corporations, universities, hospitals, and banks. In many of these applications,
A Brief History of Database Applications Read More »