1. The document discusses types of distributed databases and distributed database architecture. It describes distributed databases as collections of shared data distributed over a computer network. Distributed databases can be either homogeneous, with all sites using the same DBMS, or heterogeneous, with different sites using different DBMSs. A distributed DBMS manages the distributed database and aims to make the distribution transparent to users.

1. 1. Introduction
2. Types of Distributed Databases
3. Distributed Database Architecture

2. 1. Distributed Database System
♦ Introduction
▪ Data is stored at several sites, each managed by a DBMS(Database
Management System) that can run independently.
Distributed data independence
Users should not have to know where data is located.
- Extends physical and logical data Independence principles.
Distributed transaction atomicity
Users should be able to write transactions accessing multiple sites
just like local transactions.
Recent trends
Users have to be aware of where data is located, and distributed
transaction atomicity are not supported. For globally distributed
sites, these properties may not even be desirable due to administrative
overheads of making location of data transparent.

3. 2. Types of Distributed Databases
♦ Distributed database
A logically interrelated collection of shared data (and a description of
this data), physically distributed over a computer network.
♦ Types of Distributed database
Homogeneous:
- Every site runs same type of DBMS.
- All sites use same DBMS product.
- Much easier to design and manage.
- Approach provides incremental growth and allows increased
performance.

4. 2. Types of Distributed Databases
♦ Types of Distributed database
Heterogeneous:
- Different sites run different DBMSs (different RDBMSS or even nonrelational DBMSs).
- Sites may run different DBMS products, with possibly different
underlying data models.
- Occurs when sites have implemented their own databases and
integration is considered later.
Translations required to allow for:
- Different hardware.
- Different DBMS products.
- Different hardware and different DBMS products.
- Typical solution is to use gateways.

5. 2. Types of Distributed Databases
♦ Distributed DBMS
- Software system permits the management of the distributed database
and makes the distribution transparent to users.
- Transparent implies that each user within the system may access all of
the data within all of the databases as if they were a single database
- There should be ‘location independence’ i.e.- as the user is unaware of
where the data is located it is possible to move the data from one physical
location to another without affecting the user.