HTML5 is a new HTML standard which is still under development, but a few browsers have implemented some of its new features. The most fantastic new feature is offline Web applications, which enable users to continue interacting with Web applications and documents even when their network connection is unavailable.

Internet access via cables or fiber optics is available only from your home or office. Wireless access usually requires expensive fees if you subscribe "unlimited" plans. Besides, Web documents are loaded from your computer much faster than from the "cloud" (where the server is located). These are just a few reasons for offline use. The new offline Web applications are so powerful that they could make many desktop applications obsolete.

Offline Document Browsing

Since Web documents are loaded faster from a local computer than from the cloud, all browsers typically "cache" Web documents on the local computer. If a cached file is requested, the browser will retrieve it from the local computer, rather than from the cloud. For Internet Explorer, the cached files are stored in a folder called "Temporary Internet Files". They are called "Temporary" because its files may be deleted when the folder size exceeds a set value. With this unpredictable temporary nature, the "Work Offline" feature in IE and FireFox was not very useful.

HTML5 will include a standard for content providers to control their cached files, which may be PERSISTENT, updated, or expired after a certain period of time. Like downloaded files, cached files can be accessed anytime and anywhere even without internet connection. However, they have two major differences. (1) When a downloaded HTML file is open, it has a local address such as "file:///C:....." A cached file has exactly the same Web address as its original file in the cloud, starting with "http://......" (2) Downloaded files are no longer associated with their original files, but cached files are still linked to their original files which can be continuously updated by content providers.

Offline Web Applications

Web applications are the applications that can be understood by the browser. With the new offline feature of HTML5, they can work offline as well as online. This will make life a lot easier for both developers and users. The traditional desktop applications, such as Microsoft Office Word, are "native applications" designed for a particular operating system. They are not cross-platform. For instance, MS Office Word for Windows will not work on Mac or Linux. Therefore, if you want to develop an application for everyone, you need to develop different versions for all kinds of operating systems. Even worse, each operating system has updated versions. An application working on one version may not work on a new version. As we have known, many applications that work on Windows XP have problems with Vista.

In the past, Windows is the dominant operating system. The non-compatibility was not a big problem for developers and users. Now we have quite a few competitors: Linux, Android, iPhone, Mac, etc. If you are a developer, to design an application for all of these operating systems and their future versions will drive you crazy. If you are a user, you will be quite upset when you find that an application you bought no longer works after you switch from one computer to another based on a different operating system.

Web applications are cross-platform. They will work on all kinds of computers and devices as long as their browsers support HTML5, regardless of their operating systems and their future updates. If these Web applications can also work offline, they will have great advantage over traditional native applications. The Web EPUB Viewer is an example of offline Web applications

Local Database

The most powerful feature of HTML5 is the capability for a browser to write data in the database on a user's computer/device. This local database is called IndexedDB. With this feature, the entire book content can be stored in the database in an organized way. The Web EPUB Viewer can then retrieve the book content and add functionalities such as highlights, annotation and search. Not only can you search a single book, you may search an entire library in the database!

Author: Frank Lee
Last updated: June 25, 2011.

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