2.3.1 The HTTP Listener

The HTTP listener is what we normally think of as the web server. Its job is to receive the requests users make with their browsers, determine how to process them, then return the requested resources (along with their MIME types) to the client machines that made the request. Most of the listener's life is spent monitoring a TCP port for requests made from a web browser. Although OAS and WebDB use port 80 by default, they can be configured to use other ports.

TIP: Only one application at time can listen on a port. To run OAS and WebDB on the same machine, you must configure them to listen on different ports. For example, if OAS is listening on port 80, you could configure WebDB to listen on port 81.

The HTTP listener makes static resources available by mapping physical directories on the OAS or WebDB server to a virtual alias. These aliases are used in the URL to request a static resource that resides in the corresponding directory. The goal is to give clients a uniform way to locate a resource that is independent from the operating system of the OAS or WebDB server. For example, on an NT server, you can map the directory c:\files\public\web_stuff to a virtual directory called web . URLs that need to access resources in the directory must use the alias "web", rather than the actual directory name, to retrieve static resources.

You can configure OAS to make subdirectories beneath a mapped directory accessible from the Web; WebDB maps subdirectories by default. The subdirectory name, as defined on the server's operating system, is appended to the "root" alias of the URL. For example, if c:\files\public\web_stuff had two subdirectories named bob and sue , the virtual mapping to them would be /web/bob and /web/sue .[ 2 ]

[2] Since the Web originated mostly on Unix systems, URLs use the forward slash ("/") to denote directories, much to the chagrin of the DOS world, which uses the backslash ("\").

Since they include operating system specific names, subdirectory mappings are not completely platform independent. On Unix systems, for example, directory names are case sensitive, so the directories Junk and junk are not the same. Consequently, a URL that accesses a subdirectory on a Unix server must be case sensitive as well. Other platforms have similar caveats. The spaces in Win9x directory names cause all sorts of headaches, and the 3.x version has an eight-character limit. The best advice on any platform is to keep subdirectory names simple.

2.3.2 The PL/SQL Gateway

The PL/SQL gateway is to the database what the HTTP listener is to the filesystem:

• Just as static resources are accessed with a URL, PL/SQL dynamic resources are accessed with a URL.

• Just as physical directories are mapped to virtual directories, physical database schemas are mapped to virtual schemas. These virtual mappings are used in a URL to select the database schema in which a particular dynamic resource resides.

• Just as static resources are identified by filenames, PL/SQL dynamic resources are identified by procedure names (packaged procedures are identified with both a package and a procedure name). These names are used in a URL to select the procedure to execute.

Both OAS and WebDB use the Database Access Descriptors to connect to a specific schema, which includes all the information necessary to establish a database connection, such as a username, password, and connect string. In either case, the DAD is mapped to a virtual alias that is used within a URL to select a schema.

OAS schema mappings have two parts: a DAD, which maps a schema, and agents, which map to a DAD. The agent name, not the DAD, appears in the URL to make the connection between the Web and the database. Both the URL and the ACTION attribute of a form that requests a dynamic resource have the following general format (optional sections are bracketed):

http://
server
[
:port
]/
agent_name
/plsql/[
package.
]
procedure
[
?parm1=foo...
]

Here are a few examples:

http://gandalf/agent_webtest/plsql/print_all_emps http://gandalf/agent_webtest/plsql/show_emps?i_name=BOB http://207.25.98.87:8181/secure_agent/plsql/show_users http://betty/agent_webtest/plsql/forum.current_forum_list

WebDB has a slightly simpler mapping system that uses just the DAD in the URL; WebDB does not use agents. The URL's format is as follows (optional sections are bracketed):

http://
server
[
:port
]
/dad_name/
[
package.
]
procedure
[
?parm1=foo...
]

Here are some examples:

http://pcandrew.ora.com/WebDB/WEBDB.home http://gandalf:8181/WebDB/show_emps?I_name=FRED+FLINTSTONE http://www.travel.com/travelers_site/flights.show_list?country=FR