Distinguish between distributed database systems and decentralized databasesystems.

Distributed Database Systems and Decentralized Database Systems are two different types of data storage systems. Here's how they differ:

1. Distributed Database Systems: In a distributed database system, the data is spread across different sites, each with its own processing capabilities. These sites are connected via a network and the system is managed by a central DBMS (Database Management System). The central DBMS coordinates data distribution, ensures data consistency, and controls concurrency and recovery scenarios. The main advantage of this system is that it can improve performance by allowing queries to be processed by the local site, reducing network load. However, it requires a complex infrastructure and management.

2. Decentralized Database Systems: In a decentralized database system, there is no central DBMS. Instead, each site manages its own data and operates independently. The sites may communicate with each other, but there is no central authority controlling the entire system. This type of system is more robust and less prone to single points of failure, as each site can continue to operate even if others fail. However, ensuring data consistency across all sites can be challenging.

In summary, the main difference between the two systems is the presence of a central DBMS in distributed systems, which is absent in decentralized systems.