Atom/RSS Service Overview

The Atom/RSS (Real Simple Syndication), format is an XML-based data format used for publishing Web logs, known as blogs. The Atom syndication data format is a formalization of a variety of earlier RSS syndication data formats and addresses many of the shortcomings of those formats such as being able to handle arbitrary data in a blog and not just plain text or HTML. The Atom/RSS syndication data format is understood by most modern RSS readers and RSS related tools.

An Atom/RSS document is known as a feed and contains a set of entries each representing an independent blog. A blog commonly contains a title, author information, the date and time it was created, and then the actual data. This data may represent abstracts, headlines, full articles, references to other documents, etc.

The Decentralized Software Services (DSS) Atom Service shows how to take advantage of existing Web infrastructure in the form of Web browsers and RSS readers and merge it with the DSS service model to allow for automatic, service based interactions:

1. Users can post blogs through a regular HTML Form User Interface.
2. Users can read blogs using a standard RSS Reader such as the one provided in Microsoft Internet Explorer 7 and other browsers.
3. Services can interact with the Atom/RSS service using Decentralized Software Services Protocol (DSSP) to insert, update, delete, and query blogs. Also, by using DSSP subscriptions, they can subscribe to the Atom/RSS service and retrieve blogs as they are inserted immediately instead of having to rely on a polling model which is common for regular RSS readers.

Below is an example of the HTML form interface provided with the Atom/RSS service. When a blog is submitted through the HTML form it is inserted into the state of the service and a notification is generated and sent to all subscribers immediately using the DSSP notification model. In addition, DSSP enables blogs to be accessed and manipulated as structured data by allowing other services to query, update, delete, and otherwise modify blogs.

The service state can be accessed directly from an RSS reader such as the one provided by Internet Explorer. This allows for traditional Atom/RSS style subscriptions where the RSS reader polls the service on a regular basis. Services can also blog directly allowing for services to blog to each other as well as use blogs to report status for monitoring and filtering purposes.

In the example below the Console Output Service (see DSS System Services) blog is an example of a blog that is automatically generated by another service.

The Atom/RSS service is representative of many DSS services in that it provides a fairly complete set of functionality including features such as:

1. Web-based User Interface using XSLT (see Accessing DSS Services through a Web Browser)
2. HTML form input and Uniform Resource Identifier queries (see Accessing DSS Services through a Web Browser)
3. The definition of complex state. The state of a service is an actual Atom/RSS feed document containing XML attributes, nested lists, etc.
4. Handling of DSSP operations such as INSERT, DELETE, and UPDATE (see Accessing DSS Services through DSSP)
5. DSSP subscriptions using the Subscription Manager (see DSS System Services)
6. Subscribing to other services

While many of these topics are covered in other service tutorials (see Service Tutorials Overview), in the Atom/RSS Syndication the documentation goes through the various steps to cover these features in order to illustrate how to put together a complete service.

If the programmer just wants to try out the service you can start it from a DSS Command Prompt as follows

dsshost /p:50000 /t:50001 /m:"samples\config\atom.manifest.xml"

After the DSS node has started, the programmer can access the Atom/RSS service by pointing the Web browser at:

https://localhost:50000/atom

The HTML Form which is available by following the link titled DSS Atom Syndication Feed, enables a user to post new blogs as well as search existing blogs.

 

 

 

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