Updating replicated data in distributed database
A transaction requesting a data item will have access to the same value in all the sites.
Difference in schema is a major problem for query processing and transaction processing.
Sites may not be aware of each other and may provide only limited facilities for cooperation in transaction processing.
When discussing access to distributed databases, Microsoft favors the term distributed query, which it defines in protocol-specific manner as "[a]ny SELECT, INSERT, UPDATE, or DELETE statement that references tables and rowsets from one or more external OLE DB data sources".
Today the distributed DBMS market is evolving dramatically, with new, innovative entrants and incumbents supporting the growing use of unstructured data and No SQL DBMS engines, as well as XML databases and New SQL databases.