The objective of the chapter is to determine the position of DBMS in the information system of the organization as its essential part. Brief description of different DBMS technologies, comparison of DBMS architecture, acquaintance with data life cycle
Database (DB) is shared data connection and description dedicated for information necessity of the organization .
Database management system (DBMS) is a combination of language and software tools designed to create, maintain and share a database by many users. .
DBMS is an essential part of information system of the organization [1-3].
Information system is a resource that provides the possibility to realize data collection, modification and spread of the information inside the organization .
Typical computerized information system includes the following components:
Lets give the definition of data saving and management methods that are used by information systems of the organization .
Manual files provide the possibility to handle the information processing when quantity of objects that are saved is small. They can be used for saving and collecting big amount of data but do not fit for occasions when it is necessary to set up cross-connections or to realize the information processing. If we need any information we have to look through files from the very beginning to the end to find necessary data. To provide the possibility of the scanning some indexing algorithm is supposed to be applied. It helps to hasten data scanning. For example, it is possible to use special separator or isolated folders for different types of objects that are logically connected.
File systems is a group of programs that perform some operations, for example - reports generation. Each program identifies its own data and controls them [2, 4, 5].
File systems was the first attempt to computerize well-known manual files. They were designed due to necessity to get more efficient data access. However, instead of organizing centralized storage for all data, the decentralized system was applied. It means that employees of each department with the help of data processing experts could work with their own data and save them in their own department.
Such brief description of file systems is enough to understand their disadvantages.
Data separation and isolation causes significant complications when it is necessary to organize data processing in two within bigger quantity of files.
Data duplication causes uneconomical resources loss as additional data input requires additional time and funds. It can lead to data corruption. For example, we can get two conflicting answers for the same query in different departments of the organization. In many cases it is possible to avoid data duplication by applying common files use.
Data dependence causes significant loss in case of physical modification of the files structure that is presented in the applied software. For example after some period of industrial exploitation of the application program was found that number of bank account is increased from 10 to 16 signs due to some legislation amendments. To resolve the problem it is necessary to design a program that will be used only once. It has to open primary file, create temporary file with a new structure, to read data from primary file, to modify the data format and to log them to the temporary file, to remove primary file, to assign a name to the temporary file.
Data format incompatibility complicates data processing even more than data distribution and isolation. For example, it can be a result of data sharing between two local tasks. In such case it is necessary to create software that can convert data in one common format. That gives the possibility of coprocessing.
Rapid quantity increase of application programs for data collection , that is necessary for file systems users significantly depends on software experts as they have to create all queries and reports. The result was the following: in organizations, where software experts were absent in the staff list, types of queries and reports that were created corresponded to the determined format. There were no means of creation unplanned or spontaneous requests. In other companies that hired software experts quantity of files and application programs increased dramatically. Finally the moment came when it was already impossible to manage all queries for providing information to users.
Mentioned file systems limitation is a result of two factors.
To improve efficiency of work new principle was applied. That is DB and DBMS.
To deepen into this concept we are going study it more carefully. DB is a united data storage that is once determined and then applied by many users from different departments. Instead of spill files all data is gathered together with minimal part of excessiveness. Database doesn’t belong to only one department, but is a public resource of corporation. It contains not only work data but also its description. That is why it is called integrated logging set with self-description. Altogether this is system catalog or data-dictionary, and the elements of description are used to be called meta-data, that means "data about data". The presence of data self-description provides independence of application programs and data (program-data independents).
Today, the use of a DBMS has the following advantages:
Server is a hardware-software complex that processes the request.
As a matter of fact, it is waiting when a client will make a request and processes it. Server has to be able to process several requests from different clients at a time and also be able to determine priority. Usually server-side code works continuously to provide uninterrupted access to its service.
Clients are applications that provide a graphical or other user interface.
Application programs provide users with interface to manage server data. Through application program user gets the access to server features. Reception, splitting, modifying and deletion of the information and print-out of the report can be as an example of requested action. In this case client just sends a request and provides data necessary for its processing. Server is responsible for the request processing. It means that client ca not execute any logic operations by himself. It is possible that client implements the biggest part (or even whole volume) of business-rules support.
Business rules is a managing procedure that determines which client gets access and can handle data on the server.
These rules are implemented by program text of the client, server or both of them. From the side of server business rules are realized as saved procedures, triggers and other objects that are typical for server DB. It is important to understand that business rules determine the behavior of the whole system. If they are absent you just have data on one computer and application program with interface on another one, however you don’t have method to connect them.
If the biggest part of rules is implemented on the server, it is called “thick server”. If the rules are implemented on a medium level, server is also called “thick”. Where business rules are to be implemented is determined by the volume and type of necessary control operations.
DB on personal computers were developing from the basis of local application programs, when in fact only one application program can work with DB, up to systems of multiple access [2 – 7].
Necessity of multiple accesses to the same data caused DB transference to the file server. Application program that works with DB also was placed on the server. Method that implies saving of the application program that made a request to the DB on the user’s (client’s) computer, happened to be not so popular. New versions of local DBMS were issued. They provided possibility to create application programs that work with one DB on the file server simultaneously. The main problem was explicit or implicit transactions processing and the problem of providing semantic and reference integrity of the DB during simultaneous data modification implemented by several clients that unavoidably arises in case of shared access.
During exploitation of local systems, the following disadvantages of file-server data saving, that provides database access for many users, were detected:
Abovementioned disadvantages can be resolved by transferring from “file-server” architecture [2, 4, 5] to “client-server” architecture that is a next step in DBMS development [2…7]. Particularity of “client-server” architecture is that computing load is moved on DB server (SQL-server) and the application program of client unloaded as much as possible. There is also a significant improvement of the data protection either from ill-intentioned or erratic changes. In this case DB is located on the server as in “file-server” architecture, but there is no direct access to the DB from application programs. Service of direct connection to the DB is implemented by special control program – SQL-server that is an essential part of DBMS.
Interaction between DB and client’s application program is carried out as following: Client makes SQL-query and sends it to the server. Server that received the query carries it out and returns the result back to the client. Basically application client-program realizes interpretation of received from server data, input of the data and implementation of some business rules.
Many of already existing “client-server” programs started from application programs that applied local DB, that were shared and were placed in the personal computers network on file servers. Transfer of the file-server architecture on SQL-server DBMS was implemented to increase the efficiency of its work, safety and database reliability.
Model of “client-server” architecture supposes application of several levels. Maybe two-level model is more popular as it sticks to the scheme of local DB construction (figure 1.1.) In this model data is constantly located on the server and data access software is located on the user’s computer. At the same time business rules can be located on any computer (or even on both computers at the same time).
Fig. 1.1. Two-level "client-server" model
In three-level “client-server” architecture model (fig.1.2) in the software of the client only the interface of user is realized. It provides access to the data located on the server. Application program of the client runs request to get the access to the data through application programs server or Remote Data Broker – RDB. Usually business-rules are located on the RDB server. If client, server and business rules are spread among separate computers the designer can optimize access to data and support its integrity in case of request for any application programs in the whole system.
Fig. 1.2. Three-level "client-server" model
“Client-server” architecture has several advantages:
Data base life cycle is an essential part of information system life cycle [1, 3, 4, 6, 8]. In includes the following stages (fig. 1.3) :
Fig.1.3. Database life-cycle
For DB with a small quantity of users the life-cycle can be not very difficult. However it can become extremely complicated while designing of big DB with tens and thousands of users, hundreds of requests and application programs.
It is necessary to admit that abovementioned stages are not strictly logical, but include several repetitions of the previous steps in the form of feedback. For example some problems can arise during DB designing. To resolve these problems it will be necessary to return back to the stage of collecting and analyzing requirements. Feedback cycles can appear between almost all stages. We highlighted the most obvious ones.
“Client-server” architecture DBMS is an essential component of the up-to-date information system of the organization. DB life cycle is not separated from the life cycle of information system. Its stages and complicity of feedback depends on the kind of activity and size of the organization.
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