Web Servers

Answers to Questions about...
Web Servers

15. What is an application server?

With regard to web applications, an application server is software that mediates between a web server and back-end systems such as databases or legacy applications. Requests from a client web browser are passed by the web server to the application server, which applies logic and communicates with back-end systems as necessary to compose an HTML response returned by the web server to the requesting browser.

Other Definitions

"A program run on a mid-sized machine that handles all application operations between browser-based computers and a company's back-end business applications or databases." (PC Webopedia)

"...an application server is software that runs on a middle tier, between Web browser-based thin clients and back-end databases and business applications. Application servers handle all of the application logic and connectivity that old-style client-server applications contained. " (CNET News.com)

Example. Allaire Cold Fusion (CF) is a popular commercial application server that runs on Windows NT and Sun Solaris. A web application written for Cold Fusion consists of web pages with the .CFM extension that contain a mix of standard HTML and proprietary markup (CFML). The Cold Fusion server executes the special tags, which may for instance perform SQL operations against an ODBC-connected database, then formats the results as HTML before returning them via the web server.

Other products in the application server category are listed in Intranet Journal's Tools of the Trade.

Comment. Application servers can be as simple and inexpensive as Microsoft ASP, which comes bundled with the IIS web server; or they can cost upwards of $100K and implement complex load-balancing, security and transaction management functions. To cope with this spread, industry watchdog Zona Research distinguishes three types of app server:

1. Integrated development environments (IDE) are tools for building and hosting web-based applications capable of accessing back-end data stores. Examples as of Nov.98 include Allaire Cold Fusion, Microsoft ASP, Progress Software Apptivity Server, Sybase PowerStudio, IBM Visual Age for Java.
2. Transaction application servers emphasize security, load balancing and transaction integrity, typically for e-commerce or extranet applications. Pricier than IDEs, this class includes Bluestone Sapphire/Web, Sun Microsystems NetDynamics, Netscape Application Server, and IBM WebSphere.
3. Knowledge management servers stress process automation and integrated access to enterprise data and documents. KM platforms come from traditional document management vendors such as FileNet and Documentum, as well as newer entrants like Open Text Corporation.