Contents

Revision on database
Some of DBMS engines
The SQL language
Relational algebra and translating SQL queries to relational algebra
Selection, Projection, Rename Operation
UNION Operation , Intersection, Cross product, Set Diffrence
Natural Join, ............

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Distributed Database System

January 8, 2020

The decentralization approach to data base mirrors the natural organizational structure of companies which are logically distributed in to divisions, departments, projects and so on and physically distributed in to offices, plants, and factories each of which maintains its own operational data. Distributed Database is not a centralized database.
Distributed DB stores logically related shared data and metadata at several physically independent sites connected via network Distributed DBMS is the software system that permits the management of a Distributed DB and makes the distribution transparent to the user.

Data allocation is the process of deciding where to allocate/store particular data item. There are 3 data allocation strategies: Centralized, Partitioned, Replicated (Selective replication, Complete replication).
A distributed database system consists of a collection of sites, each of which maintains a local database system (Local DBMS) but each local DBMS also participates in at least one global transaction where different databases are integrated together.
oLocal Transaction: transactions that access data only in that single site oGlobal Transaction: transactions that access data in several sites.

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