1. 3. Distributed Database Architecture
♦ Distributed Architecture
Centralized DBMS on a network
Distributed DBMS environment

2. 3. Distributed Database Architecture
♦ Components of a DDBMS

3. 3. Distributed Database Architecture
♦ Advantages of a Distributed Database
Reduced communication overhead
Most data access is local, less expensive and performs better.
Improved processing power
Instead of one server handling the full database, we now have a collection of
machines handling the same database.
Removal of reliance on a central site
If a server fails, then the only part of the system that is affected is the relevant
local site. The rest of the system remains functional and available.
Expandability
It is easier to accommodate increasing the size of the global (logical) database.
Local autonomy
The database is brought nearer to its users. This can effect a cultural
change as it allows potentially greater control over local data.

4. 3. Distributed Database Architecture
♦ Disadvantages of a Distributed Database
- Complexity
- Cost
- Security
- Integrity control more difficult
- Lack of standards
- Lack of experience
- Database design more complex

5. 3. Distributed Database Architecture
♦ Shared-memory architecture
Examples : symmetric multiprocessors (sequent, Encore) and
some mainframes (ibm3090, bull's dps8)

6. 3. Distributed Database Architecture
♦ Shared-disk architecture
Examples : DEC's Vaxcluster, IBM's IMS/VS Data sharing

7. 3. Distributed Database Architecture
♦ Shared-nothing architecture
Examples : Teradata's DBC, tandem, Intel's Paragon,
NCR's 3600 and 3700

8. 3. Distributed Database Architecture
♦ Applications
- Manufacturing - especially multi-plant manufacturing
- Military command and control
- EFT
- Corporate MIS
- Airlines
- Hotel chains
Any organization which has a decentralized organization structure.

9. 3. Distributed Database Architecture
♦ Open database access and interoperability
• Open group has formed a working group to provide specifications
that will create database infrastructure environment where there is:
- Common SQL API that allows client applications to be written
that do not need to know vendor of DBMS they are accessing.
- Common database protocol that enables DBMS from one vendor
to communicate directly with DBMS from another vendor
without the need for a gateway.
- A common network protocol that allows communications
between different DBMSs.
• Most ambitious goal is to find a way to enable transaction to span
DBMSs from different vendors without use of a gateway.

10. 3. Distributed Database Architecture
♦ Multidatabase system (MDBS)
DDBMS in which each site maintains complete autonomy.
- DBMS resides transparently on top of existing database and file
systems and presents a single database to its users.
- Allows users to access and share data without requiring physical
database integration.
- Unfederated MDBS (no local users) and federated MDBS.

11. 3. Distributed Database Architecture
♦ Functions of a DDBMS
Expect DDBMS to have at least the functionality of a DBMS.
Also to have following functionality:
- extended communication services.
- extended data dictionary.
- distributed query processing.
- extended concurrency control.
- extended recovery services.