Dojo releases Adobe Apollo rival

The Dojo open source Ajax development toolkit project has released a beta of its Dojo Offline Toolkit. 

Dojo Offline allows developers to quickly and easily equip their Ajax services with the ability to run without an internet connection and synchronise data when the connection is re-established.

The technology essentially allows online services to operate at all times, eliminating a major barrier for online applications.

Users of online text editors, for instance, will be able to open the application and edit their documents, regardless of their network status.

Similarly, an online email client such as Gmail or Hotmail could operate in an offline mode, allowing users to read messages and prepare new emails that are sent as soon as a network connection is established.

Dojo Offline stores user data and the actual application into a local cache that is synchronised whenever a network connection is detected.

It requires users to install a 300KB runtime engine and bundles a special JavaScript library with the application's code. The runtime engine will be automatically downloaded when the user clicks a link.

The application is accessed through a regular hyperlink that can be stored in the browser favourites, as an item in the start menu or on the system's desktop. The current beta works on Windows and Mac OS X systems.

The functionality of the Dojo tool is similar to that of Adobe's Apollo platform. Currently in the alpha testing stage, Apollo is the codename for a cross-operating system application runtime. It too relies on a runtime engine of 6MB (Windows) or 8MB (Mac OS X).

To illustrate the new platform, Adobe has developed a test application with eBay that lets users download an application to access the auction service online and offline. The standalone application lets users track listed items and to list new items.

There are some major differences between the two, however. Dojo opens the application inside the existing browser, whereas Apollo puts the application in a new window.

Apollo requires developers to build a new application and user interface, while Dojo allows them to add offline capabilities by adding a few pre-fabricated lines of code to the existing online application.

Brad Neuberg, a developer with SitePen who created the Dojo Offline technology, argued that Adobe's approach is less secure because the online application is provided with full access to the local system.

Dojo, by comparison, limits local file access to prevent any data disclosures.

Neuberg also argued that delivering the application through a browser window rather than as a standalone publication makes it easier to use because the online and offline applications share a single user interface.

The requirement for users to download a runtime environment also limits the short term appeal of Apollo, according to Neuberg.

The lack of users will discourage developers from writing Apollo applications. In practice it can take up to five years for a new platform to gain critical mass, Neuberg argued in an online video demonstrating Dojo Offline.

Dojo is an independent open source project that creates Ajax developer tools. The project is supported by several software firms including AOL, IBM and Sun Microsystems.

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