Introduction to Data Management

An Overview of Data Management
15873 Tandem Computers Incorporated 1-3
Distributed
Databases—
Massive Storage
at Different Sites
A vital feature of modern online transaction processing systems is data distribution.
This feature is necessary to accommodate many applications, large numbers of users,
and a demand for extensive hardware and software resources. Data distribution is
based upon the idea of networks.
In a local network of computers, two or more machines at a particular site are
connected to permit communication with each other. Each network essentially forms
a single system with greatly enhanced computing power. In such a network, pieces of
a database are often apportioned among the different machines, creating a locally
distributed database. This kind of database gives users access to tremendous
amounts of data, with specific data items located on systems where they are most
commonly used.
In a global network, online operations are extended over long distances, with
computer power distributed across the nation and even around the world, as
illustrated in Figure 1-2. Global networks feature many processors and peripheral
devices. Large-scale applications can use the processing power of all equipment in the
network, no matter where the equipment is located. A natural extension of these vast
networks is the global database—a massive database that spans computer systems in
different geographic locations many miles apart.
More about distributed databases appears in Section 2.
Relational
Databases—
Easy and Flexible
Data Retrieval
Data management systems typically represent data in the form of records. In these
systems, a record is the basic unit of storage. Each record contains fields that hold
specific information about the item to which the record pertains. For instance, a bank
account record for Sally Jones would include fields for Sally’s name, account number,
total credits and debits, and bank balance. A particular collection of records in a
database constitutes a file. For instance, the records for all checking accounts at a
particular branch of the bank might belong to a common file. The records for all
savings accounts might belong to another file.