Platinum Edition Using HTML 4, XML, and Java 1.2
(Publisher: Macmillan Computer Publishing)
Author(s): Eric Ladd
ISBN: 078971759x
Publication Date: 11/01/98

<SCHEDULE> takes three attributes: STARTDATE indicates the date that the update schedule should take effect, STOPDATE says when its schedule should terminate, and TIMEZONE tells the offset between local time and Universal Coordinated Time (UCT). Both STARTDATE and STOPDATE are set equal to dates in the ISO 8601:1988 format (YYYY-MM-DD).

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NOTE:  STOPDATE replaces the ENDDATE attribute, which is now obsolete.

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Between the <SCHEDULE> and </SCHEDULE> tags, you can have one of three standalone tags:

•  <INTERVALTIME ... />—Specifies the time interval between updates

•  <EARLIESTTIME ... />—Indicates the earliest time during an interval that an update can occur

•  <LATESTTIME ... />—Indicates the latest time during an interval that an update can occur

Each of the above standalone tags can take one of the following attributes: DAY, HOUR, or MIN. These attributes are set to the number of days (values of 1 through 7), hours (values of 1 through 23), or minutes (values of 1 through 59) that are appropriate to your scheduling needs. To do an update every half hour, for example, you would use

<INTERVALTIME MIN=30/>

To ensure that an update happens sometime in the 10 minutes before each hour, you would use

<INTERVALTIME HOUR=1/>
<EARLIESTTIME MIN=50/>
<LATESTTIME HOUR=1/>

Inserting a schedule that calls for a weekly update every Wednesday morning at exactly 8 a.m. into the channel you’re building, you’d have the following:

<CHANNEL HREF=”http://www.server.com/channelz/subscribe.html” LEVEL=4>
   <TITLE>Channel Z</TITLE>
   <ABSTRACT>Welcome to Channel Z, your Internet movie site.</ABSTRACT>
   <LOGO HREF=”http://www.server.com/channelz/images/zlogo.gif”
   STYLE=”ICON”/>
...
   <SCHEDULE STARTDATE=”1998-08-19"> <!-- 8/19 is a Wednesday -->
      <INTERVALTIME DAY=7/>  <!- Weekly update -->
      <EARLIESTTIME DAY=7 HOUR=8/> <!-- Not earlier than 8 on Wed -->
      <LATESTTIME DAY=7 HOUR=8/>  <!-- Not later than 8 on Wed -->
   </SCHEDULE>
...
   <ITEM HREF=”http://www.server.com/new/index.html”>
      <TITLE>New Movie Releases</TITLE>
      <ABSTRACT>New releases from the major studios this
       weekend</ABSTRACT>
      <LOGO HREF=”http://www.server.com/channelz/images/new.gif”
       STYLE=”ICON”>
   </ITEM>

   <ITEM HREF=”http://www.server.com/reviews/index.html”>
      <TITLE>From the Critics</TITLE>
      <ABSTRACT>Find out what the critics said before you buy
       your ticket.</ABSTRACT>
      <LOGO HREF=”http://www.server.com/channelz/images/reviews.gif”
       STYLE=”ICON”>
   </ITEM>

   <ITEM HREF=”http://www.server.com/showtimes/index.html”>
      <TITLE>When and Where?</TITLE>
      <ABSTRACT>Find out what films are playing near you.
      </ABSTRACT>
      <LOGO HREF=”http://www.myserver.com/channelz/images/times.gif”
       STYLE=”ICON”>
   </ITEM>
...
</CHANNEL>

The code above completes your channel setup. Note that you do not have to recode your content in any way. This is a key feature of CDF—it is content-independent, so no need exists to overhaul your content as you need to do with channel authoring for other software.

With your CDF file complete, you simply place it in the root directory of your Web server and set up hyperlinks that point to it. CDF-compliant browsers, such as Internet Explorer 4, will parse the file and set up the channel.

Setting Up a Software Distribution Channel

The elements discussed in the previous sections are enough to get you going with your own Webcast channel, but CDF is able to support much more than assigning content to a channel and saying when the channel should be updated. Corporations, for example, are looking to do more and more of their software distribution over their intranets. True push technology is one way to support this objective, but not every company has the financial means to set up the necessary servers or bandwidth. A less costly solution would be to use CDF to create a software update channel by which intranet users can stay current with the most recent software releases. This section shows you how to create a CDF file specifically for software distribution.

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NOTE:  Since the initial release of the CDF standard, Microsoft has split off the CDF elements that support a software distribution channel into the Open Software Description (OSD) standard. These elements are maintained separately on Microsoft’s site at http://www.microsoft.com/standards/osd/default.asp.

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The primary element involved in creating a software distribution is <SOFTPKG>. The attributes of the <SOFTPKG> tag appear in Table 17.3.

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NOTE:  Typically, you wouldn’t have PRECACHE set to YES when you also have AUTOINSTALL set to YES because no reason exists to hold the software in a cache when it is automatically installed.

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