Database Reference
In-Depth Information
Presentation
Services
Client
Client
Application
Services
Client
Client
INTERNET
Web
Services
Client
HTML
Documents
Database
Services
Web
Server
Enterprise
Database
Database
Server
Figure 19-5
Three-tier architecture for Web database access.
product table in the relational database. The product information must be incorpo-
rated into an HTML document for the server to transmit to the browser. This has to
be done in a secure environment. Importantly, it must be done as though it is part of
a single session. This is because the user will probably complete the order and trans-
mit it back to the server for further processing and recording in the database.
Let us design a suitable architecture for the type of processing needed for the
simplest of queries described here. Consider the traditional two-tier client/server
architecture with the client at the first tier and the database server at the second
tier. In this architecture, the client handles the presentation services and the data-
base server performs the database services. Although for a simple query, the two-
tier architecture may be satisfactory for access over the local network, we need at
least one more tier to accommodate the Web server for access over the Internet.
Figure 19-5 shows such a three-tier architecture.
When the complexity of application services and logic increases, the need for a
separate application server becomes apparent. The browser interacts with the Web
server based on HTTP; if static HTML pages are requested, the Web server deliv-
ers these to the browser. If dynamic web pages with database content are needed,
the Web server passes on the request to an application server. The application server
interacts with one or more data sources to assemble a response. If there is a request
for database services, it is sent to the database server. When the responses to the
data sources are completed, the application server assembles a consolidated
response in the form of web pages and responds to the browser.
Search WWH ::
Custom Search