Nowadays, distributed database systems became part of people’s life and work. They provide fast and simple access to numerous users simultaneously with a high level of data security. The current work described Oracle distributed database, which has more than 30 years of history of development. Much attention is paid to the depiction of database structure, server, instance, architecture, and administration. The emphasis is made on the system’s mechanism of work and the interconnection between the client and the databases. The understanding of distinct characteristics of structure and performance of data provides the vision of the functioning of Oracle distributed database.
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Distributed database systems can be defined as an environment in which data in more than one database instances is accessible, notwithstanding the fact that its instance is single (Dye, 1999). Additional attention should be paid to the access to data. In some systems, users have an ability to only read data, while in others they can change it. Moreover, the reference period may vary from real time to days. Nowadays, there are numerous database instances for distributed database systems. For example, like Net is used for Oracle 8, when SQL*Net is applied for Oracle 7 (Dye, 1999).
A distributed database system contains the following components: database servers, clients, and application servers. Application servers are represented by high-capacity machines. Their function lies in running intensive utilities, like making reports. The clients are represented by the lower-capacity machines of system users, like managers. These machines usually do not have a local database. The major function of these machines is providing information to users in the comfortable and understandable format. All of the components of a distributed database system are linked with each other by a network and enable communication to networked databases.
Thus, the major functions of any database servers are the following: reliable management of information and providing an access to it in a multi-user environment, preventing unauthorized access, and providing timely and effective solutions for recovering from failures.
Oracle Distributed Database System
Oracle distributed database has a rather long history of development. Larry Ellison, Ed Oates, and Bob Miner started working on it in 1977 (Oracle, 2015). They presented their project as the first commercially available relational database management system with SQL two years later (Oracle, 2015). They continued working on it and presented the first portable version in 1983 (Oracle, 2015). Since that time, Oracle distributed database can be used on various platforms. The Oracle’s ability to perform storage procedure and triggers was introduced back in 1992 (Oracle, 2015). The development of distributed database kept up with the times and the spreading of the Internet. In 1999, Oracle distributed database could support internet protocols and enabled deployment at multitier environment (Oracle, 2015). Further steps for improvement of the database’s manageability and tuning was made in 2003 after the introduction of grid computing (Oracle, 2015). Nowadays, the researchers are working on automation and consolidation of data for making Oracle more adaptive and simpler.
Oracle distributed database system performs all of the major functions of a distributed database system noted above. The machine that runs the database management system performs all the responsibilities of the distributed database, while the application servers perform application and displaying of data. The described distributed database supports and provides full control of large space for numerous concurrent users which use various applications simultaneously. Data that is located on various machines is structured into a single logical system.
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This concurrency of actions eliminates the possibility of data contention (Oracle Corporation, 1996). The transaction performance in this distributed database is rather fast. Database users have an access to the database 24 hours per day and 7 days per week without any interruptions (Oracle Corporation, 1996). Moreover, Oracle enables selective limitation of availability of information, i.e. an administrator can limit an access to some users to specific data and applications. This distributed database has a high level of security and ability to manage the limitation and monitoring of access to data.
In the context of the current work, additional attention should be paid to portability and convertibility of Oracle. This distributed database can be transferred to be used on any operational systems. This portability can be performed with minor or no changes. Tables, their groups, and supporting objects can be replicated at different sites. Data sharing across networks can be realized between various machines and operational systems.
Oracle’s distinct features are a high quality of data access, operating systems, interfaces of users and communication protocols. They are recognized by American standard organizations, like the U.S. Government’s National Computer Security Center (NCSC) and the U.S. National Institute of Standards and Technology (Oracle Corporation, 1996). These distributed databases correspond to the U.S. Government’s FIPS127-2 standard, Entry Level of the ANSI/ISO SQL92 (Structured Query Language) standard, Orange Book Security criteria, and “supports the Simple Network Management Protocol (SNMP) standard for system management” (Oracle Corporation, 1996).
Special server performs management of the database. The Oracle Server has two languages which enable it to perform different operations. They are Structured Query Language (also known as SQL) and PL/SQL (Oracle, 2015). The first language is used for the definition and manipulation of the database. Data in this bases is stored “in a set of simple relations” (Oracle, 2015). There can be one or several tables of data with rows and columns in each of them. The definition and manipulation itself are realized by giving special commands. For example, definition language commands are used for making tables and data manipulation tables enable to update data (Oracle, 2015). The second language is applied for programming SQL statement, controlling SQL program, and writing procedure for handling failures and errors (Oracle, 2015).
This server contains the database itself and the instance (Oracle, 2015). Oracle has separate physical and logical structures (Oracle, 2015). This separation enables management of one of these structures without damaging the other. The first structure is based on the data files, redo log files, as well as control files (Oracle, 2015). The second structure contains tablespaces (a logical area of a storage) and schema objects (logical structures) (Oracle, 2015). Examples of schema objects are tables, indexes, links, etc. The overall relational design of Oracle distributed database is formed on the background of the schema objects and interrelationships between them.
The start of the database is connected with the start of background process and the system global area that is also known as SGA (Oracle Corporation, 1996). The last represents the area of memory. It enables sharing the information between users by means of combination of numerous processes and buffers of memory, i.e. Oracle instance. Processes of the distributed database and users’ represent the integral components of this instance. Oracle enables users’ work and maintenance work of the whole system, while “user processes execute the code of an application program” (Oracle Corporation, 1996).
In addition, it should be mentioned that Oracle enables sharing of one physical database via its parallel server option. This represents the significant benefit to the users and leads to the significant increase of productivity of the working process.
The Relational Database Management System
Oracle represents the relational database management system. This distributed database has numerous user-defined features, like “user-defined types, inheritance, and polymorphism” (Oracle, 2015, p. 13). Oracle’s major functions are movement data into the database, its storage there and retrieving for manipulations performed b applications (Oracle, 2015). Both logical and physical operations are performed on data. That means that the user can specify how the data should be presented and what data is required.
Oracle contains the following aspects: structures, operations, and integrity rules (Oracle Corporation, 1996). The first component is represented by the defined models used for storage of data or access to it. The examples of structures are tables, indexes, etc. Structures in the distributed database are manipulated by the evidently defined measures (also known as operations), which keep to “predefined set of integrity rules” (Oracle Corporation, 1996). These rules can be explained as laws developed and applied for governance and protection of data and structures. Thus, the data in the database is considered as one unit, where the information can be stored and from which it can be obtained at any moment of time. However, it should be noted that the information can be freely available to users. This is explained by the fact that the administrator can open or close it to others.
As it was mentioned above, a distributed database represents the set of databases on separate machines which appear to application of one single database. Thus, the data in several machines can be accessed and changed in a moment. In Oracle distributed database, each database on machines is controlled by a local server. However, the consistency is assured through the cooperation with the global distributed database. A database server performs the management functions. Clients are presented with the applications which request data from it. Every machine in the system is considered as node. These machines can perform functions of clients, servers, or both of them. It should be noted that the interconnection between client and server is direct.
Oracle distributed database enables “processing to be a split between the database server and the client programs” (Oracle, 2015, p. 110). Thus, displaying of data is performed by the computers which run the application when the service responsibilities are performed by the computer that runs relational dataset management system. The connection between the application and the database is performed through the application architectures. There are several types of these architectures: client-server, multitier, and service-oriented architecture (Oracle, 2015). The first type is starting from the initiation of a request for the performance of certain operation to the database server. Then the server requires the information concerning the access of the client application to the requested data. Unlike client-server architecture, in a multitier architecture, the application server provides a part of the information to the client. This type is more beneficial because it decreases the overload on the database server and increases the security level. The encapsulation of application functionality into services is called service-oriented architecture. This type of architecture is usually used for Web services (Oracle, 2015).
Each service has its distinct name that represents “a logical representation of a service used for client connections” (Oracle, 2015, pp. 16-18). This enables simplification of configuration of Oracle distributed database.
The communication path between databases is determined with the help of database links (Oracle, 2015). The name of this link is similar to the database’s global link.
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In addition, it should be noted that Oracle used distributed processing for performance of its operations. This means that tasks of the database are distributed among various machines of the system. At the same time, the system uses only one copy of all data and numerous transactions for accessing remote and local information and real-time changing of global database.
At the current moment, Oracle contains the great variety of different content. It is represented by text, audio, image, video, XML, and spatial (Oracle, 2015). They can be used with the help of SQL. The additional attention should be paid to the fact that request can be performed to one of this datatype of to all of them, simultaneously (Oracle, 2015).
Administrating the Distributed Database
Administering of Oracle distributed database is a rather complex process that has numerous distinct features. The first feature is that administering of each participant is performed separately and independently from administering others. That means that every single database is considered as non-distributed one. At the same time, two and more databases can cooperate with each other.
Such autonomy of administering has numerous benefits. The logical structures of companies and cooperating units and organization can be reflected in the system of nodes. The responsibility of each administrator has a greater extent of manageability and lower complexity because local database administrators have control over local information. Moreover, the possibility of damaging the whole system because of the occurrence of independent failures is low. Thus, failure of one database will not entail failure of all the databases, or considerable decrease of their productivity. At the same time, such a separation of nodes enables independent upgrading of their software.
As was noted above, Oracle distributed system provides high level of security that is confirmed by several American governmental organizations. This protection concerns to data and system. Thus, Oracle enables to prevent the unsanctioned access to database and schema objects together with audit of users’ actions (Oracle, 2015). The high level of security is reached by incorporation of the following mechanisms: authorization, restriction of access to some objects, special security policies, audit of database, and authentication (Oracle, 2015). The last represents the process of presenting the credentials to the database by the user. This is necessary for the verification of the user and assurance that he has an access to data. Authentication can be performed by the operating system or by the database (Oracle, 2015).
To summarize, Oracle distributed database represents the rational database management system with the strict hierarchical structure. This system is widely used for movement, changing, storage, and data security. One of the major benefits is enabling twenty-four-hour access and transition and amendment of the information between multiple users and databases. The computer that runs the database management system performs the distribution, when the application servers are responsible for displaying the data. The work of database is connected with the access to memory at the system global area. Oracle is based on physical and logical structures which are separated from each other. This enables management of one type of structure without harming the work of another. Moreover, different databases are also separated from each other for a similar purpose. Oracle provides both simultaneous and separate access to numerous forms of content. The work of the distributed system is performed by using SQL and PL/SQL. The first language enables definition and manipulation of database, while the second is used for programming SQL. Oracle is also characterized by high level of security that is assure by its authorization, restriction of access to some objects, special security policies, audit of database, and authentication.