HTML Help - file format

There are two types of HTML Help file format:

• Compiled HTML Help Module
  (CHM with integrated TOC, Index & Search); and
• uncompiled HTML topics
  (HTML pages with separate TOC & Index - & no Search).

HTML Help files of either type (compiled or uncompiled) can be stored on a user's computer, on a network server, or hosted on a web-site. Each type has its own advantages and disadvantages, depending upon your needs. Which type you choose for the distribution of your HTML Help will depend upon where you plan to store the files and how often you intend to update their content. The rule of thumb for creating CHM files is based on how often your Help will change. If your Help changes frequently, it is probably better to leave your Help in HTML pages and post them on a file server where everyone can gain access to them, and where you can update them easily. If your content rarely changes, you can create CHM files with Microsoft HTML Help Workshop. This compresses the HTML pages and makes a nice, portable single file for your Help system.

You should (of course) primarily be attempting to best address the needs of the users of your help, however, other secondary considerations enter the selection matrix to affect your decision. These matters include delivery options, creation tool options, network and web security access options, time constraint and delivery deadline options, and (last—but not least) your authoring skill-set and abilities.

Compare the differences using the following table:

Advantages and Disadvantages of using compiled HTML Help (CHM)

Advantages	Disadvantages
CHM files can be compressed, taking up less hard-disk space and providing more portability than an entire Web site	You are required to register the CHM before it can be used, however, once it is registered, it does not need to be registered again
Users get faster results when the CHM file is stored locally	You are required to recompile the file every time a change is made to the Help system.
A single CHM file can contain an entire Web site of HTML files	You are required to redistribute the Help file each time a CHM file is modified.
Users do not need access to the Web or the network	CHM files take up hard-disk space on the user's computer, if posted locally.

Advantages of using HTML Help

HTML Help files can be stored on either a Web server or a network file share. If they are stored on either of these, the following advantages apply:

• You can update Help content in one place and not have to worry about deploying or updating it on individual computers.
• No hard-disk space is required on a user's computer.
• If you already have a Web-based Help site, you can use its contents to create the custom AW file.
• You do not have to register Web-based Help on each user's computer.
• HTML Help does not require a hosted Web site to display Help content.

Disadvantages to using HTML Help files include the following:

• If you use HTML Help files hosted on a Web site, users must have access to the Web.
• If a Web server is used to host the Help files, you must also maintain the Web server and site.
• If a Web server or network file server share is used, users might experience slow response times when they submit queries due to network traffic or Web site loading.

A CHM file is a compressed HTML Help metafile. You can take the equivalent of an entire Web site and compile it into a CHM. It uses a special technology to combine HTML files into one file with a special directory, index, and file structure similar to a compressed drive. A CHM file can only be read by the HTML Help system and Microsoft Internet Explorer. CHM files are created by HTML Help Workshop and require creating a special project and build area where you create and organize Help topics in HTML format.

Access to CHM files can be obtained through a network share or locally on a user's computer. CHM files offer the following advantages over other file types:

If you use CHM Help files, you must deploy them to each client computer whenever you update the content.

You can use HTML Help to create two types of Help systems. You can:

• Create a compiled Help file that is viewed by using the HTML Help Viewer. This is typically the way HTML Help is used to provide help for an Office application.
• Create Web pages that use the HTML Help ActiveX control or the HTML Help JScript applet to implement navigation and secondary window features to display HTML pages and other documents from a Web browser. If you provide the appropriate value for the CODEBASE attribute when you are inserting the HTML Help ActiveX control in a Web page, the control can be installed and downloaded if it isn't already installed when a user opens the Web page. This method can be used to run a locally installed Help system, but it is more typically used to create general-purpose Web sites.

You can deploy the files that make up your HTML Help online Help system in any of the following ways:

• As a set of HTML files compiled into one or more locally installed compiled HTML Help files (.chm)
• As a set of locally installed HTML files to be accessed through the Windows file system
• As a set of HTML files to be accessed through an intranet, an extranet, or the Internet
• A combination of these formats

The advantage of using compiled HTML Help files is that you can install a single file or small set of files on each user's local drive that can be accessed without a network connection. Additionally, compiled HTML Help files use disk space much more efficiently than uncompiled HTML files, particularly on hard disks that have been formatted with the FAT file system.

The advantage of supplying the Help topics as a Web site is that you can update and add new Help topics from a single central location; however, providing Help this way requires that users have network access to your Web site. Moreover, certain features of HTML Help, such as full-text search, are available only when you are using compiled HTML Help files.

You can also provide Help topics through a combination of both standard and compiled HTML formats, most typically in the form of a locally installed compiled HTML Help file with jumps from individual topics or the table of contents to Web pages on an intranet, an extranet, or the Internet. In addition, you can display an HTML page contained in a compiled HTML Help file from Internet Explorer by using an appropriately formatted URL.

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