Distributed Data Independence: Users should be able to ask queries without specifying where the referenced relations, or copies or fragments of the relations are located.
Distributed Transaction Atomicity: Usershould be able to write transactions that access and update at several sites just as they would write transactions over purely local data
Types of Distributed Database There are two major types of distributed database systems: they are:
Homogenous distributed database
Heterogenous distributed database.
Homogenous distributed database.
The following conditions must be satisfied for homogeneous database:
The operating system use, at each location must be the same.
the operating system, must , data structures and database application used at each location must be same or compatible.
Heterogenous distributed database.
The following conditions must be satisfied for heterogenous database:
Different sites may use different schema and software.
In heterogenous systems, different nodes may have different hardware, software and data structure at various nodes or locations.
List and explain two major types of distributed database.
Architectures of Distributed Database Systems The three major distributed DBMS architectures are:
(i)Client Server (ii) Collaborating Server (iii) Middleware
Client Server Architecture: In this architecture, the Client (front end) does data presentation or processing, while the Server (back- end) does storage, security and major data processing. Client are held responsible for user-interface issues and servers manage data and execute transactions. A client-server system has one or more client processes and one or more server processes, and a client process can send a query to any one server process. Thus a client process could run on a personal computer and send queries to a server running on a mainframe.
