The distributed database management (DDBMS) component manages the global database, providing the user interface, locating data across nodes, processing local, remote, and compound queries, handling network-wide concurrency control and recovery, and translating queries and data for heterogeneous systems. The DDBMS intercepts all user requests to determine where the required data is located and coordinates the retrieval and assembly of data from multiple database management systems. Key tasks of the DDBMS include user interfacing, data location, query processing, concurrency and recovery management, and translation for heterogeneous environments.

1. Advance Database Management Systems :29
Tasks of DDBMS Component
Prof Neeraj Bhargava
Vaibhav Khanna
Department of Computer Science
School of Engineering and Systems Sciences
Maharshi Dayanand Saraswati University Ajmer

2. DDBMS component tasks:
Provides the user interface
• Distributed database management
(DDBMS) component. The distributed
database management component is the
management system for the global database.
It has many functions, including the following:
• 1. Provides the user interface.
• Location transparency is one of the major
objectives of distributed databases. Ideally,
the user neednot specify the node at which
data is located, but acts as if all data is stored
locally and accessed by the local DBMS.

3. Provides the user interface
• The local DBMS, however, is unaware of
the distribution, so only requests that can
be satisfied locally should be sent to the
local DBMS.
• The DDBMS, therefore, intercepts all
requests for data and directs them to the
proper site(s).

4. Locates the data
• 2. Locates the data.
• After receiving a request for data, the DDBMS
consults the global data dictionary to find the
node or nodes where the data is stored. If the
request can be filled entirely at the local node, it
passes the query on to the local DBMS, which
processes it.
• Otherwise, it must devise and carry out a plan
for getting the data.

5. Processes Queries
• 3. Processes queries.
• Queries can be categorized as local,
remote, orcompound.
• A local request is one that can be filled by the
local DBMS.
• Local requests are simply handed down to
the local DBMS, which finds the data and
passes it back to the DDBMS, which in turn
passes it to the user.
• (Recall that the local DBMS has no user
interface.)

6. Locates the data and Processes
Queries
• A remote request is one that can be filled
completely at another node. In this case,
the DDBMS passes the request to the
DBMS at that node and waits for the
response, which it then presents to the
user.
• A compound request, also called a global
request, is one that requires information
from several nodes.

7. Locates the data and Processes
Queries
• To process a compound request, the
DDBMS has to decompose the query into
several remote and local requests that
together will provide the information
needed. It then directs each query to the
appropriate DBMS, which processes it and
returns the data to the DDBMS.
• The DDBMS then coordinates the data
received to formulate a response for the
user.

8. Provides network-wide concurrency
control and recovery procedures.
• 4. Provides network-wide concurrency
control and recovery procedures. Although
each local DBMS is responsible for handling
update and recovery for its own data, only the
DDBMS is aware of systemwide problems.
• Network-wide concurrency control is needed to
prevent simultaneous users from interfering with
one another.

9. Provides network-wide concurrency
control and recovery procedures
• Network-wide recovery procedures are
needed because, if a local node fails,
although the local DBMS can recover its
data to its condition at the time of failure,
only the DDBMS can keep track of and
apply changes made while the node was
inactive.
• Preserving the ACID properties for
transactions in the distributed databases is
a complex task that is handled by the
DDBMS.

10. Provides translation of queries and
data in heterogeneous systems
• 5. Provides translation of queries and data in
heterogeneous systems.
• In heterogeneous systems with different
hardware but the same local DBMS, minor
translations of codes and word lengths and
slight changes due to differences in
implementation are needed.

11. Provides translation of queries and
data in heterogeneous systems
• If the local DBMSs are different, major
translation is needed. This includes
changing from the query language of one
DBMS into that of another and changing
data models and data structures.
• If both hardware and DBMSs are different,
both types of translation are needed.

12. Assignment
• Explain the DDBMS component tasks.