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An introduction to RSS news feeds
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var emailAbstract = "RDF Site Summary (RSS) is catching on as one of the most widely used XML formats on the Web. Find out how to create and use RSS files and learn what they can do for you. See why companies like Netscape, Userland, and Moreover use RSS to distribute and syndicate article summaries and headlines. This article includes sample code that demonstrates elements of an RSS file, plus a Perl example using the module XML::RSS."; Skip to main content Country/region[ select ] All of dW----------------- AIX and UNIX Information Mgmt Lotus Rational Tivoli WebSphere----------------- Architecture Autonomic computing Java technology Linux Multicore acceleration Open source SOA & Web services Web development XML----------------- dW forums -----------------alphaWorks-----------------All of IBMHomeBusiness solutionsIT servicesProductsSupport & downloadsMy IBM developerWorksIn this article: What exactly are these RSS files?Creating RSS filesThe four main sections of an RSS fileNow start working with RSS filesPublishing your RSS fileParsing RSS filesResourcesAbout the authorRate this page Related links Web development technical libraryXML technical library
developerWorks > Web development | XML >An introduction to RSS news feedsUsing open formats for content syndication Document optionsDocument options requiring JavaScript are not displayed
Hey there! developerWorks is using Twitter Follow usRate this page Help us improve this contentLevel: IntroductoryJames Lewin (jim@lewingroup.com), President, The Lewin Group 10 Nov 2000RDF Site Summary (RSS) is catching on as one of the most widely used XML formats on the Web. Find out how to create and use RSS files and learn what they can do for you. See why companies like Netscape, Userland, and Moreover use RSS to distribute and syndicate article summaries and headlines. This article includes sample code that demonstrates elements of an RSS file, plus a Perl example using the module XML::RSS.
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RDF Site Summary (RSS) files, based on XML, provide an open method ofsyndicating and aggregating Web content. Using RSS files, you can createa data feed that supplies headlines, links, and article summaries from yourWeb site. These files describe a channel of information that can includea logo, a site link, an input box, and multiple "news items." Other sitescan incorporate your information into their pages automatically. You canalso use RSS feeds from other sites to provide your site with current newsheadlines. These techniques let you draw more visitors toyour site and also provide them with up-to-date information.What are metadata?RSS files are a type of metadata. Metadata are:units of information about information.commonly used to provide descriptive information about the content, context,and characteristics of data.HTML keywords and description metatags are examples of metadata, andare used to provide information about Web pages.The RSS format originated with the sites My Netscape and My UserLand,both of which aggregate content derived from XML news feeds. Because it'sone of the simplest XML applications, RSS found favor with many developerswho need to perform similar tasks. Users include Moreover, Meerkat, UserLand,and XML Tree. This article looks at the RSS format and examines some opensource Perl modules that will allow you to work with RSS files easily.What exactly are these RSS files?RSS files are metadata (see the sidebar What are metadata?). Untilyou've used them or seen an example, it may not be easy to understand whatRSS files are, but they are easy to create. An RSS file commonly containsfour main types of elements: channel, image, items, and text input. Theseelements are easy to identify and code, as the example in Listing 1 demonstrates.An example of an item within an RSS 0.91 file, Listing 1 contains threeeasily identifiable parts: a title, a link, and a description.Listing 1. A sample item in RSS<item> <title>Mozilla Dispenses with Old, Proprietary DOM</title> <link>http://www.mozillazine.org/talkback.html?article=604</link> <description>The Mozilla team has decided to forgo backwards compatibility with Netscape's proprietary DOM.</description>In headline collections published as results of RSS file aggregations,HTML normally renders the specified title as a headline. The title usuallyalso serves as a link, using the URL listed in the link element. Finally,the description is normally displayed as a summary of the article underneaththe headline.  Back to topCreating RSS filesYou can build RSS files to either the proposed RSS 1.0 specification,or to the currently more popular RSS 0.91 spec. For production applications,use RSS 0.91, because the 1.0 proposal is still under consideration. TheResources section, at bottom, includes links toboth the 1.0 and 0.91 specs. which provide a detailed review of all elements.This discussion focuses on the most commonly used elements, and all theexamples in this article are in 0.91 format.The 1.0 proposal differs from the 0.91 format in one main way: It incorporatesResource Description Framework (RDF) elements that allow greater flexibilityat the expense of some increased complexity. This proposed specificationis more extensible, creating a W3C standard for RSS files that will meetcurrent needs, will be as backwards-compatible as possible, and will beadaptable to future requirements.Both versions of the specification share the characteristic of beinga lightweight format that developers can use for many purposes.RSS is an XML application. Because of this, all RSS documents beginwith the XML 1.0 declaration followed by the RSS document type declaration,as shown in Listing 2.Listing 2. The XML declaration<?xml version="1.0"?><!DOCTYPE rss PUBLIC "-//Netscape Communications//DTD RSS 0.91//EN" "http://my.netscape.com/publish/formats/rss-0.91.dtd"><rss version="0.91">The first line declares the document to be an XML document. The secondline, the DTD declaration, specifies that this XML file is based on theRSS 0.91 document type definition, DTD, at Netscape. Finally, the rootelement marks the beginning of the RSS file content, all of which goesbetween the <rss version "0.91"> tag and the </rss> tag.Back to topThe four main sections of an RSS fileAfter the root element come the four main sections of the RSS file.These are the channel,image, item, and text inputsections. In practical use, the channel and item elements are requirementsfor any useful RSS file, while the image and text input are optional.The channel sectionThe channel element contains metadata that describe the channel itself,telling what the channel is and who created it. The channel is a requiredelement that includes the name of the channel, its description, its language,and a URL. The URL is normally used to point to the channel's source ofinformation.Listing 3 shows the beginning of the channel element. This part of thechannel element defines the channel and begins the channel information.Listing 3. The channel element<channel> <title>MozillaZine</title> <link>http://www.mozillazine.org</link> <description>Your source for Mozilla news, advocacy, interviews, builds, and more! </description> <language>en-us</language></channel>The channel element contains the remaining channel tags, which describethe channel and allows it to be displayed in HTML. The title can be treatedas a headline link with the description following. The Channel Languagedefinition allow aggregators to filter news feeds and gives the renderingsoftware the information necessary to display the language properly.The </channnel> tag is used after all the channel elements to closethe channel. As RSS conforms to XML specs, the element must be well formed;it requires the closing tag.You can include nine optional tags in a 0.91 channel definition. Someexamples are PICS Rating, Copyright Identifier, Publication Date, and Webmaster.You can use these additional elements for a variety of purposes. For example,sites that aggregate content can use this additional meta information toallow users to filter news feeds on the basis of Platform for InternetContent Selection (PICS) ratings. For additional information on other Channeltags, look in the RSS specifications.The image sectionThe image element is an optional element that is usually used to includethe logo of the channel provider. The default size for the image is 88pixels wide by 31 pixels high, but you can make your logo as large as 144pixels wide by 400 pixels wide. Here is a sample image element:Listing 4. The image element<image> <title>MozillaZine</title> <url>http://www.mozillazine.org/image/mynetscape88.gif</url> <link>http://www.mozillazine.org</link> <width>88</width> <height>31</height></image> The image's title, URL, link, width, and height tags allow renderersto translate the file into HTML. The title tag is normally used for theimage's ALT text. Keep the image to 88 x 31 or smallerif possible, because many renderers translate channels into fixed widthtables as narrow as 100 pixels. Larger graphics could cause the tablesto break inappropriately, or cause your image to be left out when displayed.The itemsItems, the most important elements in a channel, usually form the dynamicpart of an RSS file. While channel, image, and text input elements createthe channel's identity and typically stay the same over long periods oftime, channel items are rendered as news headlines, and the channel's valuedepends on their changing fairly frequently. Here is an example of a channelitem:Listing 5. The item element<item> <title>Java2 in Navigator 5?</title> <link>http://www.mozillazine.org/talkback.html?article=607</link> <description>Will Java2 be an integrated part of Navigator 5? Read more about it in this discussion...</description></item>Fifteen items are allowed in a channel. This is a reasonable limitation,because most people use channels to distribute recent Web content. Titlesshould be less than 100 characters, while descriptions should be under500 characters. The item title is normally rendered as a headline thatlinks to the full article whose URL is provided by the item link. The itemdescription is commonly used for either a summary of the article's contentor for commentary on the article. News feed channels use the descriptionto highlight the content of news articles, usually on the channel owner'ssite, and Web log channels use the description to provide commentary ona variety of content, often on third-party sites.Much of the beauty of the RSS format lies in the item element. As youcan see from the above example, items are easy for developers to defineand easy for users to read.The text inputThe text input area is an optional element, with only one allowed perchannel. Usually rendered as an HTML form, text input lets the user respondto the channel. You might use this feature to enable your users to subscribeto your newsletter or search your site. Here is an example of a text inputelement:Listing 6. The text input element<textinput> <title>Send</title> <description>Comments about MozillaZine?</description> <name>responseText</name> <link>http://www.mozillazine.org/cgi-bin/sampleonly.cgi</link></textinput>The title is normally rendered as the label of the form's submit button,and the description as the text displayed before or above the input field.The text input name is supplied along with the contents of the text fieldwhen the submit button is clicked.These are the four main elements of an RSS file. After adding the image,item, and text input elements, remember to close the channel with the </channel>tag and the RSS file with the </rss> tag.The proposed RSS 1.0 specification introduces modules, which will allowRSS to be extended to accommodate additional information without rewritingthe specification. For example, you could write a module to add rich mediato your channel for broadband clients while standard clients would stillsee headlines and descriptions. You may want to learn more about modulesso that you can take advantage of them once the 1.0 specification is implemented.Back to topNow start working with RSS filesThere are several ways to start working with RSS files. Because RSSfiles are so simple, they can be created easily using any text or XML editor.Also, there are sites with Web forms that let you create a custom RSS fileonline. Finally, you will also want to try creating RSS files automatically.Open-source tools for Java, PHP, and Perl can help you get started (see Resources for some examples).Once you have created a simple RSS file, you will want to validate it.You can do this at Netscape's site, listed below in the Resources section.Post the RSS file on a publicly accessible area of your Web site, go toNetscape's site, submit your URL, and the validator will test your filefor compatibility.Back to topPublishing your RSS fileOnce you have a valid RSS file available on your Web site, you cansyndicate your content. You can do this in a publish and subscribe fashion-- you publish the information, and anyone who wants to can subscribe --or you can submit your URL to content aggregators such as Moreover or Userland.Aggregators take content from a variety of sites and publish it in feeds.While your site's information could be mixed in with content from a varietyof other suppliers, aggregators can help you dramatically extend the reachof your distribution.You can also use RSS files for private distribution on intranets orextranets. Their simplicity makes RSS files a good way to publish informationto a variety of systems.Back to topParsing RSS filesOnce you start working with RSS files, you will want to parse the fileback into discrete units of information. You can do this with the helpof a variety of open-source tools written in Java, Perl, PHP, and evenASP. The parser reads a stream of XML text, identifies the opening andclosing tags, finds the text enclosed in each tag, and creates handlesto work with the parsed information. Once parsed, this information canbe incorporated into dynamically generated pages.Listing 7 shows a simple Perl program that reads RSS files.Even if you don't write Perl, the example might give you some ideas thatyou can use in your own development environment.Perl is a great language for manipulating RSS files; there is a substantialamount of open-source code readily available to help get you started. JonathanEisenzopf has developed the XML::RSS module, which writes and parses RSSfiles. To take advantage of this parser, you will also need theXML::Parser module. These two Perl modules are available for free at CPAN(see Resources).Here is an example of how XML:RSS can be used:Listing 7. A Perl example using XML::RSS# Setup includesuse strict;use XML::RSS;use LWP::Simple;# Declare variables for URL to be parsedmy $url2parse;# Get the command-line argumentmy $arg = shift;# Create new instance of XML::RSSmy $rss = new XML::RSS;# Get the URL, assign it to url2parse, and then parse the RSS content$url2parse = get($arg);die "Could not retrieve $arg" unless $url2parse;$rss->parse($url2parse);This code sample passes a URL to a Perl script for parsing. Once parsed,the elements of the RSS file can be used in many ways. For example, youcould use RSS items to create a list of headlines:Listing 8. Making headlines with Perl# Print the channel itemsforeach my $item (@{$rss->{'items'}}) { next unless defined($item->{'title'}) && defined($item->{'link'}); print "<li><a href="http://www-128.ibm.com/developerworks/library/w-rss.html/\"$item->{'link'}\">$item->{'title'}</a><BR>\n";}This sample loops through the array of RSS items, verifying that eachitem comes complete with a title and link. Incomplete items are skipped;complete items are included in a list of linked headlines.If you plan to use the XML::RSS module, open and read it with any texteditor; it is heavily commented with suggestions for using it effectively.Once you have tried your hand at RSS files, you'll find that there aremany ways that you can use them. For example, you can write scripts thatgenerate RSS summaries every time your site is updated, or scripts thatperiodically retrieve news from other sites and automatically update yourown news page. (How to write those scripts is fodder for another article, but you may find some useful open-source tools to automatically generate RSS summaries in the tool sources listed in Resources.I've offered a few suggestions for creating and using RSSfiles. The resource section provides additional information, such as sourcesfor RSS files, the RSS specifications, and places where you can post yourheadlines.ResourcesLearnThe RSS2.0 Specification site contains general information such asbackground, motivation, and design goals as well as the working specification.The W3C Recommendation for the RDF model and syntax specification is containedat ResourceDescription Framework.Netscape originated the format as RSS 0.9. Their site features an overviewof RSS 0.9 and has the recent specifications.My Userland aggregatesheadlines from a variety of sources. It was one of the first sites to useRSS files.Get products and technologiesWebreference has an online RSSChannel Editor that is a great way to get started making RSS files.WirelessDeveloper Network has tools for parsing RSS files with PHP.Moreover is an aggregatorthat features free news feeds from over 1,500 news sources.Meerkatis an RSS-based syndicated content reader, as well as a source for newsfeeds.About the authorJames Lewin has been working with the Internet since 1995, but he didn't go wireless until 2000. He is the President and owner of The Lewin Group a Networking and Internet Solutions provider. He is an MCSE who also works with Microsoft and open source Internet development tools.Rate this pagedocument.write(''); Please take a moment to complete this form to help us better serve you.Did the information help you to achieve your goal?YesNoDon't know Please provide us with comments to help improve this page: How useful is the information?12345NotusefulExtremelyuseful
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