Record- based data models such as the relational data model, network data model, and hierarchical data model see Section 2. Physical data models describe how data is stored in the computer see Section 2. Provide justification for your answer. Concurrency Control Services - only single user. Authorization Services - only single user, but may be needed if different individuals are to use the DBMS at different times.
Utility Services - limited in scope. Support for Data Communication - only standalone system. Exercises 2.
- Distributed Database Management Systems: A Practical Approach;
- Distributed Database Management Systems: A Practical Approach;
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What type of language does each system provide? What type of architecture does each DBMS use? Check the accessibility and extensibility of the system catalog. Is it possible to export the system catalog to another system? To do this you will need to obtain appropriate information about each system. There should be manuals available or possibly someone in charge of each system who could supply the necessary information.
Write another program that stores names and addresses in a database. Modify the programs to use external, conceptual, and internal schemas. What are the advantages and disadvantages of this modification? The programs can be written in any suitable language and should be well structured and appropriately commented. Two distinct files result. The structures can be combined into one containing name, address, and telNo, which can be the representation of both the internal and conceptual schemas.
The conceptual schema should be created separately with a routine to map the conceptual to the internal schema. The two external schemas also must be created separately with routines to map the data between the external and the conceptual schema. The two programs should then use the appropriate external schema and routines.
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Extend the program so that it stores the format of the data in the database; in other words, create a system catalog. Provide an interface that makes this system catalog accessible to external users. Again, the program can be written in any suitable language. It should then be modified to add the data format to the original file.
This should not be difficult, if the original program is well structured. The interface for other users operates on the data dictionary and is separate from the original program. A menu-based interface is adequate. Compare the client-server architecture with two other architectures. The client is a process that requires some resource, and the server provides the resource. Neither need reside on the same machine. Why is the latter architecture more appropriate for the Web?
See Figures 3. The three-tier architecture can be expanded to n tiers, with additional tiers providing more flexibility and scalability. Provide a classification service for middleware. Middleware is a generic term used to describe software that mediates with other software and allows for communication between disparate applications in a heterogeneous system.
The need for middleware arises when distributed systems become too complex to manage efficiently without a common interface. The need to make heterogeneous systems work efficiently across a network and be flexible enough to incorporate frequent modifications led to the development of middleware, which hides the underlying complexity of distributed systems. A TP Monitor forms the middle tier of a three-tier architecture. A DBMS that supports this standard can function as a resource manager under the control of a TP Monitor acting as a transaction manager.
We discuss distributed transactions and the DTP standard in Chapters 23 and In addition, it can dynamically bring in additional DBMSs as required to provide the necessary performance. In many cases, we would find that users generally do not need continuous access to the DBMS. This allows a larger number of users to access the available DBMSs with a potentially much smaller number of connections, which in turn would mean less resource usage.
Web services allow applications to integrate with other applications across the Internet and may be a key technology that supports B2B Business to Business interaction. Unlike other Web- based applications, Web services have no user interface and are not aimed at Web browsers. Web services instead share business logic, data, and processes through a programmatic interface across a network. In this way, it is the applications that interface and not the users.
Developers can then add the Web service to a Web page or an executable program to offer specific functionality to users. It is both platform- and language-independent. Figure 3.
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From the database perspective, Web services can be used both from within the database to invoke an external Web service as a consumer and the Web service itself can access its own database as a provider to maintain the data required to provide the requested service. The SOA approach attempts to design loosely coupled and autonomous services that can be combined to provide flexible composite business processes and applications. An example of SOA is shown in Figure 3. This is a major DBMS component that transforms queries into a series of low-level instructions directed to the database manager.
The DM interfaces with user-submitted application programs and queries.
The DM accepts queries and examines the external and conceptual schemas to determine what conceptual records are required to satisfy the request. The DM then places a call to the file manager to perform the request. The file manager manipulates the underlying storage files and manages the allocation of storage space on disk.
It establishes and maintains the list of structures and indexes defined in the internal schema. However, the file manager does not directly manage the physical input and output of data. Rather, it passes the requests on to the appropriate access methods, which either read data from or write data into the system buffer or cache. This module converts DML statements embedded in an application program into standard function calls in the host language.
The DML preprocessor must interact with the query processor to generate the appropriate code. These tables are then stored in the system catalog while control information is stored in data file headers. The catalog manager manages access to and maintains the system catalog. The system catalog is accessed by most DBMS components. Oracle is based on the client—server architecture. The Oracle server consists of the database the raw data, including log and control files and the instance the processes and system memory on the server that provide access to the database.
An instance can connect to only one database.
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The database consists of a logical structure, such as the database schema, and a physical structure, containing the files that make up an Oracle database. Exercises 3. The client application runs both business logic and the code to display output to the user, and is also known as a thick client. SQL Server enables data to be consumed from custom applications developed using Microsoft.
Web services extend the World Wide Web infrastructure to provide the means for software to connect to other software applications. Web services combine the best aspects of component-based development and the Web, and are a cornerstone of the Microsoft. NET programming model. NET Framework. The client runs the database application that accesses database information and interacts with a user through the keyboard, screen, and pointing device, such as a mouse. The server runs the Oracle software and handles the functions required for concurrent, shared data access to an Oracle database.
Although the client application and Oracle can be run on the same computer, greater efficiency can often be achieved when the client portions and server portion are run by different computers connected through a network. Most organizations implement service-oriented architecture SOA with the hope of gaining more business agility through reuse of shared services.
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As reuse begins to take hold within the organization, however, it becomes critical to manage consumption of services or your SOA can quickly spin out of control. Oracle Web Services Manager provides a solution for governing the interactions with shared services through security and operational policy management and enforcement to ensure service reuse remains under control.
Leading companies are gaining operational efficiencies and business agility through adaptable, re-usable business processes and services built on a truly flexible Service-Oriented Architecture SOA foundation. Oracle plans to continue to develop and support Oracle WebLogic Integration, and expects to converge this product with Oracle's strategic solutions over time.
See all DBST courses. Advantage and Disadvantage of Distributed Database. Distributed Database Management Systems. The chapter starts slowly, gradually telling us that when a database has end users who are separated across large distances, their experience suffers if the database is only located on one central device. Access may be requested across a company network or across the Internet.
Introduction to Distributed Database Management Systems. Each Distributed Database Management System takes part in at least one global application. Secured management of distributed data — Various transparencies like network transparency, fragmentation transparency, and replication transparency are implemented to hide the actual implementation details of the whole distributed system. In such way, Distributed database provides security It can be defined as A distributed database DDB is a collection of multiple logically related database distributed over a computer network, and a distributed database management system as a software system that manages a distributed database while making the distribution transparent to the user.
Shared nothing architecture.