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Active Channel Types
This section describes basic types of channels that properly use the strengths of the Microsoft® Internet Explorer information delivery architecture within the constraints of bandwidth available in the home or the corporation. Web publishers can create channels to take advantage of the following three key Internet Explorer 4.0 capabilities.
Notification Internet Explorer 4.0 uses a red "gleam" (resembling an asterisk) to visually flag the logos and icons of channels that have changed since their previous update. Users can choose to have an e-mail message sent to them when a channel is updated. Sitemap The Channels Explorer Bar can display a navigable outline of URLs as specified in a channel's CDF file. The exposed hierarchy of the channel helps users efficiently navigate through a channel to find the content they are most interested in. Offline Content Caching Internet Explorer 4.0 downloads the set of resources specified in the CDF file to be locally cached. This allows users to browse through the entire content of an active channel even when they are offline. It is important to note that offline content is available only to users accepting the default "download content" option when subscribing to the channel. Channel Sitemaps and Notifications
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These capabilities can, of course, be combined to create different types of end-user channel experiences. It's important to realize, however, that this flexibility also permits authors to define impractical channels (for example, a channel that tries to replicate an extensive Web site to the user's local disk). As a general rule, an Active Channel should fit into one of these categories: news, immersion, or notification. A hybrid channel is also possible.
News Channels
A news channel is used to keep the user up to date on breaking news. This channel periodically Webcasts a hierarchically structured set of news items to the desktop, through the CDF file. The actual content referenced in the CDF file is downloaded into the user's cache and is available for offline use. A news channel uses all three Internet Explorer key capabilities: notification, sitemap, and offline content caching. When developing the content for a news channel, keep the following guidelines in mind:
- Each news item is a discrete, simple, self-contained page.
- Each news item page is designed to be small.
- The page should consist mainly of text and utilize Dynamic HTML layout features.
- Pages should reuse and/or minimize the use of images, especially large ones.
The CDF file allows Web publishers to hierarchically organize items in a channel into subchannels. The TITLE of each subchannel serves to classify the items contained within the subchannel. By default, subchannels and items in the channel's CDF are displayed in an outline format in the Channels Explorer Bar. In addition to any navigation mechanism authored into the pages themselves, the user can expand and collapse subchannels in the outline and jump to individual news items.
Example: A news publisher, Action News, generates business stories as individual HTML pages.
Today's business stories are:
- A daily summary of the stock market
- URL: http://www.action.com/channel/bus/bus001.htm
- Title: "The Market"
- Abstract: "Summary of today's market news."
- An article on the general economy
- URL: http://www.action.com/channel/bus/bus002.htm
- Title: "Business nirvana: low inflation, high growth"
- Abstract: "Best environment for business in 25 years due to convergence of factors."
- An article on rise in technology issues
- URL: http://www.action.com/channel/bus/bus003.htm
- Title: "Tech stocks soar on XYZ Corp. news"
- Abstract: "XYZ Corp. showed unexpected growth this quarter, dragging up prices through the technology segment."
The pages are primarily textual, sharing a common masthead graphic, as shown here.
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For the purpose of this example, the publisher's channel consists of only these stories organized into a single subchannel called The Market. The publisher could deliver these articles to the desktop by providing the following CDF file:
<?XML VERSION="1.0" ENCODING="UTF-8"?> <CHANNEL href="home.htm" BASE="http://www.action.com/channel/" > <TITLE>Action News</TITLE> <ABSTRACT>Description of the Action News Channel</ABSTRACT> <LOGO href="actionlogo16x16.gif" STYLE="ICON"/> <LOGO href="actionlogo32x80.gif" STYLE="IMAGE"/> <SCHEDULE STARTDATE="1997-10-17" STOPDATE="1997-10-17"> <INTERVALTIME DAY="1"/> </SCHEDULE> <CHANNEL href="bus001.htm"> <TITLE>The Market</TITLE> <ABSTRACT>"Summary of today's market news"<ABSTRACT> <LOGO href="marketlogo.gif" STYLE="ICON"/> <ITEM href="bus002.htm" LASTMOD="1997-10-17T11:12"> <TITLE>Business nirvana: low inflation, high growth</TITLE> <ABSTRACT>Best environment for business in 25 years due to convergence of factors.</ABSTRACT> <LOGO href="topstorylogo.gif" STYLE="ICON"/> </ITEM> <ITEM href="bus003.htm" LASTMOD="1997-10-17T11:12"> <TITLE>Tech stocks soar on XYZ Corp. news </TITLE> <ABSTRACT>XYZ Corp. showed unexpected growth this quarter, dragging up prices through the technology segment.</ABSTRACT> <LOGO href="topstorylogo.gif" STYLE="ICON"/> </ITEM> </CHANNEL> </CHANNEL>Once subscribed to by the user, Action News would appear within the browser's Channels Explorer Bar as:
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Since none of the stories in the CDF include the PRECACHE="NO" attribute on the ITEM elements, all of the pages will be precached during updating. Therefore, each news page will be available for offline viewing if the user subscribes to the channel and chooses to receive channel content.
Immersion Channels
An immersion channel presents the user with an authored "environment" that provides all navigation (for example, the Channels Explorer Bar is assumed to be hidden). All content is precached so the channel can be used offline. It is important to note that this channel's items and subchannels do not appear in the Channels Explorer Bar. In this case, the CDF file is used exclusively to specify content that needs to be downloaded and to notify the user when the channel has been updated. Downloading channel content helps increase online performance and allows offline use. Similar to the CDF of a news channel, the author specifies a list of items to be updated and a schedule for updating them. However, unlike a news channel, each item in the CDF must include the following child element:
<USAGE VALUE="None"></USAGE>This element instructs Internet Explorer 4.0 not to display the subchannel or item in the Channels Explorer Bar, but it will download and precache each item. Resources other than HTML pages, such as images and ActiveX controls, can also be specified in the CDF to be precached when the channel is updated. Since the channel is designed for offline use, the amount of content specified by the CDF file must be compatible with bandwidth constraints of the target audience.
Example: A maze game immersion channel containing a set of interlinked rooms implemented as HTML pages. On each subsequent update of the CDF file, the publisher dynamically generates a new CDF file that adds new rooms or modifies the existing maze.
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The CDF file to deliver a simple maze game might look something like this:
<?XML VERSION="1.0" ENCODING="UTF-8"?> <CHANNEL href="home.htm" BASE="http://www.gamer.com/channel/" > <TITLE>The Castle</TITLE> <ABSTRACT>An always changing maze of rooms for you to explore</ABSTRACT> <LOGO href="castle16x16.gif" STYLE="ICON"/> <LOGO href="castle32x80.gif" STYLE="IMAGE"/> <SCHEDULE STARTDATE="1997-10-17" STOPDATE="1997-10-17"> <INTERVALTIME DAY="1"/> </SCHEDULE> <ITEM href="room01.htm" LASTMOD="1997-10-17T11:12"> <USAGE VALUE="None"></USAGE> </ITEM> <ITEM href="room02.htm" LASTMOD="1997-10-17T11:12"> <USAGE VALUE="None"></USAGE> </ITEM> <-- a list of additional items --> <ITEM href="roomnn.htm" LASTMOD="1997-10-17T11:12"> <USAGE VALUE="None"></USAGE> </ITEM> </CHANNEL>
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Notification Channels
A notification channel informs the user when new information is available within a channel and provides a sitemap (through the CDF file) to the new information without downloading the content itself. The CDF file of a notification channel is similar to a news channel, except that the PRECACHE= attribute of each subchannel and item is explicitly set to "NO". The hierarchy of items and subchannels in the CDF file is displayed in the Channels Explorer Bar, but the content referenced by the outline is available only online. It's important that the publisher sets the user's expectations appropriately, specifically indicating that this type of channel is designed to notify the user of changes to content available online. Like all channels, a "gleam" appears on the channel's logo to inform the user that the channel has been updated.
Example: A corporation wants to create a channel to notify employees about the latest information on their employee services, benefits, company policies, and so on.
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The following illustrates the notification channel's CDF file. The example includes only the Employee Services subchannel.
<CHANNEL href="home.htm" BASE="http://www.corp.com/channel/" PRECACHE="No"> <TITLE>Corporate Channel</TITLE> <ABSTRACT>CorpCo's Corporate Channel</ABSTRACT> <LOGO href="corplogo16x16.gif" STYLE="ICON"/> <LOGO href="corplogo32x80.gif" STYLE="IMAGE"/> <SCHEDULE STARTDATE="1997-10-17" STOPDATE="1997-10-17"> <INTERVALTIME DAY="1"/> </SCHEDULE> <-- omitted subchannels --> <CHANNEL href="services.htm" PRECACHE="NO"> <TITLE>Employee Services</TITLE> <ABSTRACT>Employee services from CorpCo</ABSTRACT> <LOGO href="categorylogo.gif" STYLE="ICON"/> <ITEM href="companystore.htm" PRECACHE= "NO" LASTMOD="1997-10-17T11:12"> <TITLE>Company Store</TITLE> <ABSTRACT> Offerings from the company store </ABSTRACT> <LOGO href="bulletlogo.gif" STYLE="ICON"/> </ITEM> <ITEM href="stockservices.htm" PRECACHE= "NO" LASTMOD="1997-10-17T11:12"> <TITLE>Stock Services</TITLE> <ABSTRACT>Buying and selling CorpCo stock</ABSTRACT> <LOGO href="bulletlogo.gif" STYLE="ICON"/> </ITEM> <ITEM href="career.htm" PRECACHE= "NO" LASTMOD="1997-10-17T11:12"> <TITLE>Career Center</TITLE> <ABSTRACT>Job opportunities at CorpCo</ABSTRACT> <LOGO href="bulletlogo.gif" STYLE="ICON"/> </ITEM> <ITEM href="handbook.htm" PRECACHE= "NO" LASTMOD="1997-10-17T11:12"> <TITLE>Employee Handbook</TITLE> <ABSTRACT>Rules and regulations for CorpCo employees</ABSTRACT> <LOGO href="bulletlogo.gif" STYLE="ICON"/> </ITEM> <ITEM href="cafeteria.htm" PRECACHE= "NO" LASTMOD="1997-10-17T11:12"> <TITLE>Cafeteria Menus</TITLE> <ABSTRACT>Today's eats </ABSTRACT> <LOGO href="bulletlogo.gif" STYLE="ICON"/> </ITEM> <ITEM href="vacation.htm" PRECACHE= "NO" LASTMOD="1997-10-17T11:12"> <TITLE>Vacation and Sick Reporting </TITLE> <ABSTRACT>Vacation and sick day reporting form </ABSTRACT> <LOGO href="bulletlogo.gif" STYLE="ICON"/> </ITEM> </CHANNEL> <-- omitted subchannels --> </CHANNEL>Hybrid Channels
Hybrid channels combine two or more of the news, immersion, and navigation channel types. When creating a hybrid channel, follow these guidelines:
- Remember that the total daily download from any channel, including hybrid channels, must take into account bandwidth limitations.
- Segregate items that can be used offline from those that must be used online into discrete subchannels. Therefore, the subchannels of a hybrid channel should fall into one of the three basic channel types previously discussed. For example, a single hybrid channel that delivers news-style items for offline reading and provides a sitemap to an online site might look like this:
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Design Guidelines for Active Channels
To take true advantage of the "push" mechanism available in Internet Explorer 4.0, channels must be as small as possible to minimize download time and provide compelling content and interaction when used offline. When designing your Active Channel, follow these guidelines:
- Design your channel to conform to one of the Active Channel types previously described in this document. Some channels, of course, might naturally cross the boundaries.
- Channels intended for offline use (news and immersion channels, for example) should consider the impact of bandwidth limitations. If the target user is a home user dialing over a modem, the average amount of content delivered per update, per channel should be no more than 500K to 1 MBpreferably smaller. Under ideal conditions, a megabyte of content can be downloaded by a 28.8K modem in about six minutes. In practice, however, depending on line and server conditions, downloading 1 MB takes about 10 minutes. The following table shows download connect times for a 28.8K modem for different numbers of channels under different line conditions.
Number of 500K 500K 1 MB 1 MB channels (ideal) (typical) (ideal) (typical) 2 6 min. 10 min. 12 min. 20 min. 4 12 min. 20 min. 24 min. 40 min. 8 24 min. 39 min. 49 min. 80 min. 12 36 min. 59 min. 73 min. 120 min. Note Sizes represent the average amount of data downloaded per channel.
- Active Channels should be self-contained. The channel must deliver real value to the user while offline. It is likely that users will become annoyed with an offline channel that constantly forces online connections. This means that links to noncached resources should be minimized or hidden when the user is offline. Scripting can be used on an HTML page to determine when the user is offline and reflow the page accordingly using Dynamic HTML.
- Channels should be personalized whenever possible. A publisher can provide a personalized channel experience for each user by generating a custom CDF for each user (for example, based on user preferences stored in a cookie). Channels based on personalized CDF files can be more rapidly delivered because content that is not important to the user will not be downloaded. Generating a customized CDF is as easy as offering a personalized home page using server-side scripting.
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