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06.14.04
 By
Scott
Mitchell
With the rise of always-on Internet connections in homes and businesses,
and the continued explosive growth of the World Wide Web and Internet-accessible
applications, it is becoming more and more important for applications
to be able to share data with each other. Sharing data among disparate
platforms requires a platform-neutral data format that can be easily
transmitted via standard Internet protocols-this is where XML fits
in. Since XML files are essentially, simple text files with well-known
encodings, and since there exist XML parsers for all commonly used
programming languages, XML data can be easily consumed by any platform.
A good example of data-sharing using XML is Web site syndication,
commonly found in news sites and Web logs. With Web site syndication,
a Web site publishes its latest content in an XML-formatted, Web-accessible
syndication file. There are a number of syndication formats in use,
one of the more popular ones being RSS 2.0. (RSS
2.0 Specification is published online at the Technology at Harvard
Law site.) Additionally, MSDN® Magazine has a syndication file, MSDN
Magazine: Current Issue, which lists the most recent MSDN Magazine
articles with links to the online version. |
Once
a Web site has publicly published a syndication file, various clients
may decide to consume it. There are a number of ways to consume a
syndication file. Someone who runs a .NET resource Web site might
want to add the latest MSDN Magazine article headlines on their Web
site. Syndication files are also commonly consumed by news aggregator
applications, which are applications designed specifically to retrieve
and display syndication files from a variety of sources.
With this growing emphasis on XML data, being able to work with XML
data in an ASP.NET Web page is more pertinent now than ever before.
Since Web site syndication is becoming all the rage, in this article
we'll build a Web site syndication file generator as well as an online
news aggregator application. As we work on these two mini-projects
throughout this article we'll examine how to access and display XML
data from both a remote Web server and from the local file system.
We'll look at how to display XML data in a myriad of ways, such as
using a Repeater control and using the ASP.NET XML Web control.
Since I do not have limitless space for this article, I will assume
that you are currently familiar with XSLT and XPath. If this is not
the case, consider reading the following resources before continuing
with this article:
FAQ:
What is XSLT and How Does it Relate to XML?
XSL Tutorial
XPath Tutorial
Syndicating Content with RSS 2.0
The first mini-application we will be building in this article is
a syndication file generator. For this mini-application, imagine that
you work as a Web developer for a large news site (like MSNBC.com)
where all of the news stories are stored in a Microsoft® SQL Server™
2000 database. Specifically, the articles are stored in a table called
Articles with the following germane fields:
ArticleID-an
auto-increment primary key integer field uniquely identifying each
article.
Title-a varchar(50), specifying
the title of the news item,
Author-a varchar(50), specifying
the author of the news item,
Description-a varchar(2000),
providing a more in-depth description of the news
item, and
DatePublished-a datetime
indicating the date the news item was published.
Note that there might be other fields in the Articles table, but those
listed above are the only fields we are interested in using for syndication.
Furthermore, this is a very simplified data model; in a real-world
setting you would likely have a more normalized database, such as
having a separate table for authors, a many-to-many table joining
authors and articles, and so on.
Our next step is to create an ASP.NET Web page that will display a
list of the most recent news items as a properly formatted RSS 2.0
XML file. Before examining how to accomplish this transformation in
an ASP.NET Web page, let's first take a moment to examine the RSS
2.0 specification. While looking over the specification, keep in mind
that RSS is designed to provide a data model to syndicate content.
Not surprisingly, then, it has a series of XML elements for information
about the Web site syndicating the content, as well as a series of
XML elements to describe a particular news item. Finally, don't forget
that RSS syndication files, like any XML-formatted file, must adhere
to XML formatting guidelines, namely that:
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All XML elements be properly nested,
All attribute values be quoted, and
All instances of < , >, &, " and ' be replaced
with < , > , & , " and '
, respectively.
Furthermore, XML files are case-sensitive, meaning that the opening
and closing tags for an XML element must match in case as well as
in spelling.
The root element in an RSS 2.0 file is the <rss> element. You
can provide the version number in this element like so:
rss version="2.0"
...
</rss>
The <rss> element has a single child element, <channel>,
which describes the syndicated content. Inside the <channel>
element there are three required children elements that are used to
describe information about the syndicating Web site. These three elements
are:
title-Specifies
the name of the syndication file, and typically includes the Web
site's name,
link-the URL
to the Web site, and
description-a
short description of the Web site.
There are a number of optional elements to describe the Web site as
well; see the RSS 2.0 Specification
for more information on these elements.
Each news item is placed within an individual <item> element.
The <channel> element can have an arbitrary number of <item>
elements. Each <item> element can have a variety of children
elements, the only requirement being that the <item> contain
at minimum either the <title> element or the <description>
element as a child. A list of the more germane <item> children
elements follows:
title-the title
of the news item,
link-the URL to
the news item,
description-a
brief synopsis of the news item,
author-the author
of the news item, and
pubDate-the published
date of the news item.
A very simple RSS 2.0 syndication file is shown below. You can see
another example RSS
2.0 file from RSS generated by Radio UserLand.
<rss version="2.0">
<channel>
<title>Latest DataWebControls.com FAQs</title>
<link>http://datawebcontrols.com</link>
<description>
This is the syndication feed for the FAQs
at DataWebControls.com
</description>
<item>
<title>Working with the DataGrid</title>
<link>http://datawebcontrols.com/faqs/DataGrid.aspx</link>
<pubDate>Mon, 07 Jul 2003 21:00:00 GMT</pubDate>
</item>
<item>
<title>Working with the Repeater</title>
<description>
This article examines how to work with the Repeater
control.
</description>
<link>http://datawebcontrols.com/faqs/Repeater.aspx</link>
<pubDate>Tue 08 Jul 2003 12:00:00 GMT</pubDate>
</item>
</channel>
</rss>
One important thing to note here is the <pubDate> element's
formatting. RSS requires that the date be formatted according to RFC
822, Date and
Time Specification, which starts with an optional three-letter
day abbreviation and comma, followed by a required day, then the three-letter
abbreviated month, and then the year, followed by a time with time-zone
name. Also notice that the <description> child element in the
<item> element is optional: the first news item lacks a <description>
element, while the second news item has one.
*This article originally appeared on the ASP.NET
Dev Center at MSDN
About the Author:
Scott
Mitchell, author of five ASP/ASP.NET books and founder of 4GuysFromRolla.com,
has been working with Microsoft Web technologies for the past five
years. An active member in the ASP and ASP.NET community, Scott is
passionate about ASP and ASP.NET and enjoys helping others learn more
about these exciting technologies. For more on the DataGrid, DataList,
and Repeater controls, check out Scott's book ASP.NET Data Web Controls
Kick Start (ISBN: 0672325012). Read his blog at : http://scottonwriting.net
Read this newsletter at:
http://www.webproasp.com/2004/0614.html |
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