Database System architectures

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Centralized and C/S (Client/Server) architectures:

Refer the below link for this topic

Server Systems:

A server operating system also called a server OS, is an operating system specifically designed to run on servers, which are specialized computers that operate within a client/server architecture to serve the requests of client computers on the network.

Distributed Systems:

A distributed system is a network that consists of autonomous computers that are connected using a distribution middleware. They help in sharing different resources and capabilities to provide users with a single and integrated coherent network.


Distributed Databases - Homogeneous and Heterogeneous databases:


Homogeneous Distributed Databases Management SystemIn homogeneous distributed database, all sites have identical software and are aware of each other and agree to cooperate in processing user requests. ... A homogeneous DBMS appears to the user as a single system..



Homogeneous Distributed Databases

In a homogeneous distributed database, all the sites use identical DBMS and operating systems. Its properties are −


The sites use very similar software.


The sites use identical DBMS or DBMS from the same vendor.


Each site is aware of all other sites and cooperates with other sites to process user requests.


The database is accessed through a single interface as if it is a single database.
Types of Homogeneous Distributed Database

There are two types of homogeneous distributed database −


Autonomous − Each database is independent that functions on its own. They are integrated by a controlling application and use message passing to share data updates.


Non-autonomous − Data is distributed across the homogeneous nodes and a central or master DBMS co-ordinates data updates across the sites.
Heterogeneous DatabaseIn a heterogeneous distributed database, different sites have different operating systems, DBMS products and data models. The system may be composed of a variety of DBMSs like relational, network, hierarchical or object-oriented. Query processing is complex due to dissimilar schemas
Heterogeneous Distributed Databases

In a heterogeneous distributed database, different sites have different operating systems, DBMS products and data models. Its properties are −


Different sites use dissimilar schemas and software.


The system may be composed of a variety of DBMSs like relational, network, hierarchical or object-oriented.


Query processing is complex due to dissimilar schemas.


Transaction processing is complex due to dissimilar software.


A site may not be aware of other sites and so there is limited co-operation in processing user requests.
Types of Heterogeneous Distributed Databases


Federated − The heterogeneous database systems are independent in nature and integrated together so that they function as a single database system.


Un-federated − The database systems employ a central coordinating module through which the databases are accessed.




Distributed Data Storage:


https://www.geeksforgeeks.org/distributed-database-system/



Distributed transactions


A distributed transaction is a database transaction in which two or more network hosts are involved. Usually, hosts provide transactional resources, while the transaction manager is responsible for creating and managing a global transaction that encompasses all operations against such resources. Wikipedia


Commit Protocols:




Concurrency control in distributed systems 




Availability

Simply stated, availability is the condition wherein a given resource can be accessed by its consumers. So in terms of databases, availability means that if a database is available, the users of its data—that is, applications, customers, and business users—can access it.


Distributed query processing




Heterogeneous distributed databases 







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