The Programmable Web reports that as of Nov 2008 it has 1,000 Web APIs on its directory.
You can see the distribution below (which looks pretty balanced all around) with Mapping APIs at the top:
And what is the preferred way to expose and consume Web APIs? The following chart shows REST at the top, with SOAP second:
(my recommendation, to use RESTful calls and XML Feeds, and consider JSON for mobile-to-server Data Interchange)
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The ProgrammableWeb web API directory now has 900+ open web service APIs, see the API Dashboard.
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A lot of noise recently, triggered by the recent S3 Outage, on the fragility of Web Services…
And guess what? This is (and will continue to be) a recurring and expected theme on the highly interdependent world of Mashups and services on the web.
When having such dependencies, you need to take the time to understand the robustness of the services/platform that you are depending on, and make sure there is a good Service Level Agreement (SLA) in place. And then, wish for the best, because web services do and will fail on you. So, if you have critical dependencies, you must do infrastructure and capacity planning (see below), and contemplate going with a redundant fail safe approach, but that is going to cost you extra (as in time and money).
Note that Amazon S3 does have what seems a reasonable SLA.
Related to this see:
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The beautify of services on the web — Mashups.
As of today, there are 2800 registered Mashups (The Programmable Web):
Every day of the year we get new mashups get added to our directory and as of yesterday the total was an even 2800 mashups. To build these, developers have used 315 different web service APIs. Which includes a lot of APIs that are not maps. One way to see this is by using the APIs by Mashups view which shows an ordered list of how many mashups we have cataloged per API. The pie chart below shows the distribution by API over the past two weeks:
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Are you? Hey, there is nothing wrong with being one and enjoying life… REST is very simple to use, more and more services on the web are getting exposed using REST, and recently the Restlet API was introduced.
For those new to REST, Representational State Transfer or REST, is the result of Roy Thomas Fielding PhD Dissertation, an HTTP-based model for the programmatic consumption of web content and services, that uses URIs for representing “items” on the web, and the HTTP methods GET, PUT, POST and DELETE to operate on them. Returned data is typically in XML.
Examples of Web 2.0 REST-based APIs include: Yahoo!, which has been exposing most of its services using REST, for example see Creating a REST Request for Yahoo! Search Web Services, and the Flicker's REST API.
While the latest Google APIs are not really REST-based, there is XooMLe, which allows you to query the Google search engine and have your results returned in XML. I am not really sure about Google's APIs strategy, and if their APIs will get exposed using REST.
Bottom line is that REST-based services are simple to consume, and simplicity is always a winner.
Update: Interview of Jerome Louvel, Restlet project founder.
"Great individuals invent their own values and create the very terms under which they excel." -Kierkegaard and Nietzsche