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Components of a Distributed Database System

In this context there are described major components of distributed database system. Because there are many commercial DDBMS, the used terminology in this text is not the only one. User Request Interface is typically a client program that acts as an interface to the Distributed Transaction Manager and accepts user's requests for transactions. The distributed transaction manager is a program that translates requests from the user and converts them into actionable requests for the database managers, which are typically distributed. A Database Manager is software which is responsible for processing a segment of the distributed database. Together, the distributed transaction managers and the database managers make up the DDBMS (see Fig. gif). A node is a piece of hardware that can implement either a transaction manager, a database manager, or both. Distributed database systems can be comprised of infinitely many architectures. This characteristic is key for maintaining a system that is to be scalable. For instance, it is possible for DBMSs to be a collection of mainframes, minicomputers, or even PC's, or any combination contained therein. This can allow for scalable systems which integrate all three types of computers into one system.

 
Figure: A Distributed Database  

There are two types of DDB technologies. The first one is synchronous technology, which provides application integrity and minimizes complexity, but can be slow and less available if the systems and networks involved are unreliable and slow. The second one is asynchronous technology which maximizes availability and response time performance, but is more complicated and requires a lot of planning and design. Understanding the tradeoffs between these two technologies is the key to determining which to use to solve a certain problem.

It will be a while before full flexibility is reached, but the more complicated it gets, the more important it is to develop standards for transaction management, concurrency controls, security, backup, recovery, query optimism, access path selection and more.

Since the inception of the Internet, viewing documents on it became much easier for users by developing a set of protocols. Status quo is WWW. In order to encourage people to use the WWW, graphical user interfaces (GUI) were developed to allow users to interact on the Internet easily.

Now that WWW standards are well established, other companies adopted them in creating their own software for different uses. Among the most notable software program, is ORACLE which is used as a powerful relational database system. Further software developments now enable linking the ORACLE DB environment with the WWW by allowing ORACLE functions to take place directly on line.

If distributed database tables are designed with standard protocol codes to enable access within a highly secure environment, then there is much potential in using the WWW for viewing and managing distributed databases. With security protocol codes it will be easy to access valuable information from such things as viewing store inventories to publicly allowed financial data or even do your own banking on the Net.


next up previous contents
Next: Advantages and disadvantages Up: Distributed Databases Previous: Distributed Databases

Heikki Hy|tyniemi
Tue Aug 5 14:39:14 EET DST 1997