Database Reference
In-Depth Information
you have a database server machine and as many client machines as needed. The
server on one tier and the clients on the other tier form this two-tier architecture.
The server and the clients are usually linked on a LAN.
The following briefly describes how a two-tier system may apply to distributed
databases.
•
The server performs all database functions. Based on query requests, the server
retrieves the requested data and passes them on to the requesting client. It also
updates the database as required by executing transactions.
•
The client manages the user interface, interprets queries and transactions, and
routes them to the appropriate servers. When data is received from the server,
the client presents the information to the user. If a query requires data from
multiple sites, the client breaks up the query into appropriate subqueries and
routes each subquery to the proper server. When results are received from
multiple servers, the client consolidates the result sets and presents the con-
solidated result to the user.
The two-tier architecture clearly demarcates the functions of the server and the
client. Each side can be suitably configured for high performance. The server can
be made robust enough with sufficient memory, storage, and computing power to
carry out its database functions. But, when you look at the configuration of the
client, it must also be powerful and have software to interpret queries, create sub-
queries, and route them properly. And every client machine must be so configured.
This is not an inexpensive option.
Intelligent Server Architecture (Two Tier)
This is also a two-tier option. Let us
go over this option and inspect how this can work in a distributed database envi-
ronment. As in the previous case, at each site you have a database server machine
and as many client machines as needed. The server on one tier and the clients on
the other tier form this two-tier architecture. The server and the clients are usually
linked on a LAN.
The server and the clients serve the following functions.
•
The server performs all database functions. Based on query requests, the server
retrieves the requested data and passes them on to the requesting client. It also
updates the database as required by executing transactions. If a query requires
data from multiple sites, the server breaks up the query into appropriate sub-
queries and routes each subquery to the proper server. When results are
received from multiple servers, the local server consolidates the result sets and
sends the merged result to the requesting client.
•
The client manages the user interface, receives query and transaction input, and
sends them to the local server at that site. When data are received from the
server, the client presents the information to the user.
Although the two-tier architecture clearly demarcates the functions of the server
and the client, we have just shifted some functions to the server from the clients.
This relieves the clients from being too heavy. However, now the servers must
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