Components of the DBMS Environment
We can identify five major components in the DBMS environment: hardware, software,
data, procedures, and people, as illustrated in Figure 1.8.
Hardware
The DBMS and the applications require hardware to run. The hardware can range from
a single personal computer, to a single mainframe, to a network of computers. The particular
hardware depends on the organization’s requirements and the DBMS used. Some
DBMSs run only on particular hardware or operating systems, while others run on a wide
variety of hardware and operating systems. A DBMS requires a minimum amount of main
memory and disk space to run, but this minimum configuration may not necessarily give
acceptable performance. A simplified hardware configuration for DreamHome is illustrated
in Figure 1.9. It consists of a network of minicomputers, with a central computer
located in London running the backend of the DBMS, that is, the part of the DBMS that
manages and controls access to the database. It also shows several computers at various
locations running the frontend of the DBMS, that is, the part of the DBMS that interfaces
with the user. This is called a client–server architecture: the backend is the server and the
frontends are the clients. We discuss this type of architecture in Section 2.6.
Software
The software component comprises the DBMS software itself and the application programs,
together with the operating system, including network software if the DBMS is being used
over a network. Typically, application programs are written in a third-generation programming
language (3GL), such as ‘C’, C++, Java, Visual Basic, COBOL, Fortran, Ada, or
Pascal, or using a fourth-generation language (4GL), such as SQL, embedded in a thirdgeneration
language. The target DBMS may have its own fourth-generation tools that allow
rapid development of applications through the provision of non-procedural query languages,
reports generators, forms generators, graphics generators, and application generators. The
use of fourth-generation tools can improve productivity significantly and produce programs
that are easier to maintain. We discuss fourth-generation tools in Section 2.2.3.
Data
Perhaps the most important component of the DBMS environment, certainly from the
end-users’ point of view, is the data. From Figure 1.8, we observe that the data acts as a
bridge between the machine components and the human components. The database contains
both the operational data and the metadata, the ‘data about data’. The structure of
the database is called the schema. In Figure 1.7, the schema consists of four files, or
tables, namely: PropertyForRent, PrivateOwner, Client, and Lease. The PropertyForRent table has
eight fields, or attributes, namely: propertyNo, street, city, postcode, type (the property type),
rooms (the number of rooms), rent (the monthly rent), and ownerNo. The ownerNo attribute
models the relationship between PropertyForRent and PrivateOwner: that is, an owner Owns
a property for rent, as depicted in the Entity–Relationship diagram of Figure 1.6. For
example, in Figure 1.2 we observe that owner CO46, Joe Keogh, owns property PA14.
The data also incorporates the system catalog, which we discuss in detail in Section 2.4.
Procedures
Procedures refer to the instructions and rules that govern the design and use of the database.
The users of the system and the staff that manage the database require documented
procedures on how to use or run the system. These may consist of instructions on how to:
n log on to the DBMS;
n use a particular DBMS facility or application program;
n start and stop the DBMS;
n make backup copies of the database;
n handle hardware or software failures. This may include procedures on how to identify
the failed component, how to fix the failed component (for example, telephone the
appropriate hardware engineer) and, following the repair of the fault, how to recover the
database;
change the structure of a table, reorganize the database across multiple disks, improve
performance, or archive data to secondary storage.
People
The final component is the people involved with the system. We discuss this component
in Section 1.4.
We can identify five major components in the DBMS environment: hardware, software,
data, procedures, and people, as illustrated in Figure 1.8.
Hardware
The DBMS and the applications require hardware to run. The hardware can range from
a single personal computer, to a single mainframe, to a network of computers. The particular
hardware depends on the organization’s requirements and the DBMS used. Some
DBMSs run only on particular hardware or operating systems, while others run on a wide
variety of hardware and operating systems. A DBMS requires a minimum amount of main
memory and disk space to run, but this minimum configuration may not necessarily give
acceptable performance. A simplified hardware configuration for DreamHome is illustrated
in Figure 1.9. It consists of a network of minicomputers, with a central computer
located in London running the backend of the DBMS, that is, the part of the DBMS that
manages and controls access to the database. It also shows several computers at various
locations running the frontend of the DBMS, that is, the part of the DBMS that interfaces
with the user. This is called a client–server architecture: the backend is the server and the
frontends are the clients. We discuss this type of architecture in Section 2.6.
Software
The software component comprises the DBMS software itself and the application programs,
together with the operating system, including network software if the DBMS is being used
over a network. Typically, application programs are written in a third-generation programming
language (3GL), such as ‘C’, C++, Java, Visual Basic, COBOL, Fortran, Ada, or
Pascal, or using a fourth-generation language (4GL), such as SQL, embedded in a thirdgeneration
language. The target DBMS may have its own fourth-generation tools that allow
rapid development of applications through the provision of non-procedural query languages,
reports generators, forms generators, graphics generators, and application generators. The
use of fourth-generation tools can improve productivity significantly and produce programs
that are easier to maintain. We discuss fourth-generation tools in Section 2.2.3.
Data
Perhaps the most important component of the DBMS environment, certainly from the
end-users’ point of view, is the data. From Figure 1.8, we observe that the data acts as a
bridge between the machine components and the human components. The database contains
both the operational data and the metadata, the ‘data about data’. The structure of
the database is called the schema. In Figure 1.7, the schema consists of four files, or
tables, namely: PropertyForRent, PrivateOwner, Client, and Lease. The PropertyForRent table has
eight fields, or attributes, namely: propertyNo, street, city, postcode, type (the property type),
rooms (the number of rooms), rent (the monthly rent), and ownerNo. The ownerNo attribute
models the relationship between PropertyForRent and PrivateOwner: that is, an owner Owns
a property for rent, as depicted in the Entity–Relationship diagram of Figure 1.6. For
example, in Figure 1.2 we observe that owner CO46, Joe Keogh, owns property PA14.
The data also incorporates the system catalog, which we discuss in detail in Section 2.4.
Procedures
Procedures refer to the instructions and rules that govern the design and use of the database.
The users of the system and the staff that manage the database require documented
procedures on how to use or run the system. These may consist of instructions on how to:
n log on to the DBMS;
n use a particular DBMS facility or application program;
n start and stop the DBMS;
n make backup copies of the database;
n handle hardware or software failures. This may include procedures on how to identify
the failed component, how to fix the failed component (for example, telephone the
appropriate hardware engineer) and, following the repair of the fault, how to recover the
database;
change the structure of a table, reorganize the database across multiple disks, improve
performance, or archive data to secondary storage.
People
The final component is the people involved with the system. We discuss this component
in Section 1.4.
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