Web components 101

By Jon Udell

August 30, 1999

(Exploring XML-RPC :  Page 2 of 5 )

In this Article

Exploring XML-RPC Web components 101 The XML Dimension Anatomy Of An XML-RPC Transaction DCOM? CORBA? RMI? Why Not Just XML-RPC?

call Web APIs. For example, part of Alta Vista's Web API is a

method that might be formalized as:

getReferenceCount ( sitename )

My href="http://img.byte.com/byte/features/1999/03/19990308_udell.perl">mindshare-measuring

script invokes what might be called a Web RPC on the Alta Vista site in order to count references to a target

site. You don't have to write scripts to use Web RPCs; we do this

trivially when we save bookmarks to CGI-based services (e.g., a

bookmark to an Alta Vista query, not its result). But when you

automate the use of these RPCs, you can create new and interesting

applications.

To do that involves a process that I call reverse-engineering

the Web API. In the case of Yahoo, the relevant API is just its

tree-structured URL namespace (e.g.

/Computers_and_
Internet/Software/Operating_Systems/Windows/).

In the case of Alta Vista, it's a CGI-style URL built on this pattern:

http://www.altavista.com/cgi-bin/query?pg=q&kl=XX&q=link%3A{SITENAME}+-url%3A{DOMAIN}

Here {SITENAME} and {DOMAIN} are, effectively,

function-call arguments; the script plugs in real values for these

arguments and then "calls" the Alta Vista "component." Alta Vista's

Web API is easy to discover because it uses the HTTP get method; that

means the URL you need to parameterize is left sitting in the

browser's location (Netscape) or address (Microsoft) field. When a

site uses the HTTP Previous page Page 2 of 5 Next page

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