Distributed Database and
• A logically interrelated collection of shared
data and a description of this data
physically distributed over a computer
– All sites use the same DBMS product.
– Sites may run different DBMS products.
• Fragmented allocation:
– Partition the database into disjoint fragments, with
each fragment assigned to one site where they are
used most frequently.
• Horizontal fragment
• Vertical fragment
• Complete replication
– Maintain a complete copy of the database at each
• Selective replication
– Mixed of fragmentation and replication
Extending ANSI-SPARC Model to
• Global External view at each site
• Global Conceptual schema
• Fragmentation and Allocation schemas
• Local schemas
Advantages and Disadvantages of
– Improved availability
– Improved reliability
• Distributed query processing, concurrency control, recovery
– Integrity control more difficult
Synchronous versus Asynchronous
• Synchronous replication:
– Replicated data is updated immediately.
• Asynchronous replication:
– Replicated data is updated after the source
database has been modified.
– Data ownership:
• which site has the privilege to update the data.
• Asynchronous replicated data is owned by one
site, the master site, and can be updated only by
– Decision support system analysis
– Distribution and dissemination of centralized
– Consolidation of remote information
• Replicated copy can be update locally and then brought
together in one location.
– Mobile computing
• It is a complete or selective part of a
database that is consistent with the
database at a specific point in time.
– Create Snapshot
– Refresh Snapshot
• Complete refresh
• Differential refresh
Replication in ADO.Net
Adapter Data Reader
• It is read-only and forward-only cursor.
• A DataSet object can hold several tables
and relationships between tables.
• A DataSet is a set of disconnedted data.
Data is extracted from the database and
stored in the DataSet object. Updates to
the DataSet must copy back to the
database to make the changes