A distributed database, or, if properly named, a distributed database is a database that includes several computers connected by a network, each running a local database. The aggregate of all these firmware creates a common database. Distributed databases from the outside look like ordinary local databases, their hardware diversity is not visible to users. The distributed control system monitors all nodes of the database and ensures data connectivity.
Christopher Day, a renowned database specialist with a worldwide reputation, identified twelve major properties that all distributed databases should have: 1) local autonomy, 2) continuous operations, 3) node independence, 4) transparent fragmentation, 5) transparency of location, 6) processing of certain requests, 7) transparent replication, 8) independence from the equipment, 9) processing of distributed transactions, 10) network transparency, 11) independence from the operating system, 12) independence from the selected databases.
Consider the main qualities that, according to Data, should have all the distributed databases, in more detail.
Local autonomy means that each node independently manages its database.
Continuous operations. At this point, K. Dayt says that access to data must be ensured continuously and regardless of which node they are located on. Also, it should not matter what operations the local database is currently performing.
Independence of nodes. In an ideal system, all nodes are equal in rights and do not depend on each other. Each database located on the node supplies data to a common space with the same rights. All databases that make up a distributed database are self-contained and protected from access by outsiders.
Transparency of location. A user accessing distributed databases does not need to know anything about which nodes the information required is physically located.
Processing distributed requests. The database must execute distributed query queries in the SQL language.
Transparent replication. In general, replication is the transfer of changed objects from one database to another. In the context of this material, we mean the transfer of data between nodes in ways that ensure that these actions are invisible to the user.
The independence of the equipment means that the nodes of the distributed database network can be any computer model.
Distributed transaction processing is treated as a way to update a distributed database using the UPDATE, DELETE, and INSERT commands, which do not lose the integrity and consistency of information stored in the database.
OS independence means that the system nodes can run under any operating system.
Transparency means that only a network connection is required to access all elements of a distributed database.
Independence from databases. This important feature requires the system to work with all distributed DBMS from different vendors, including search and update capabilities.
As we see, the definition of K. Data for a distributed database describes it as a structure with weak links, consisting of independent nodes that are local databases. These LBDs are autonomous, and distributed DBMSs from different manufacturers provide access to them. Nodes form relationships among themselves, which are replicable data. The topology of the distributed database forms the geography of the information system and data replication flows.