2. What is a distributed database?

A distributed database is a single logical database whose parts are physically located in more than one place, each location is accessible across a network.

A standard database on a network looks like this

This shows a central database being accessed from a workstation over a network.

Note that all traffic has to flow over the network, and this may be a problem.

A typical distributed database looks like this:

In this case the database is split across different sites and each site is connected over a network.

Each site has a database management system (DBMS) that allows queries and updates to be made locally. But each site also has a distributed database component (DDBMS) that allows each site to make global queries of the whole system.