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Overview of webOS


    
On this page and those that follow you can read the first chapter of Palm webOS: Developing Applications in JavaScript using the Palm© Mojo™ Framework by Mitch Allen, chief technology officer of software at Palm, Inc. This is the official guide to building native JavaScript applications for webOS™.

Palm webOS offers you a complete tutorial on the design principles, architecture, UI, tools, and services necessary to develop webOS applications. Visit the O'Reilly web site for more information about the book or to purchase it. Also, view the O'Reilly webcast, Developing Applications for webOS, also presented by Mitch Allen.
    

Palm© webOS™ is Palm's next generation operating system. Designed around an incredibly fast and beautiful user experience and optimized for the multi-tasking user, webOS integrates the power of a window-based operating system with the simplicity of a browser. Applications are built using standard web technologies and languages, but have access to device-based services and data.

Palm webOS is designed to run on a variety of hardware with different screen sizes, resolutions and orientations, with or without keyboards and works best with a touchpanel though doesn't require one. Because the user interface and application model are built around a web browser, the range of suitable hardware platforms is quite wide, requiring only a CPU, some memory, a wireless data connection, a display, and a means for interacting with the UI and entering text.

You can think of webOS applications as native applications, but built from the same standard HTML, CSS and JavaScript that you'd use to develop web applications. Palm has extended the standard web development environment through a JavaScript framework that gives standardized UI widgets, and access to selected device hardware and services.

The user experience is optimized for launching and managing multiple applications at once. WebOS is designed around multi-tasking, and makes it utterly simple to run background applications, to switch between applications in a single step, and to easily handle interruptions and events without losing context.

You will build WebOS applications with common web development tools following typical design and implementation practices for Ajax applications. But your webOS applications are installed and run directly on the device, just as you are used to doing with native applications.

Application Model

As shown in Figure 1-1, the original Palm OS has a typical native application model, as do many of the popular mobile operating systems. Under this model the application's data, logic and user interface are integrated within an executable installed on the native operating system, with direct access to the operating system's services and data.

Figure 1-1. Native and Web Application Models

Classic web applications are basic HTML-based applications that submit an HTTP request to a web server after every user action, and wait for a response before displaying an updated HTML page. More common in recent years are Ajax applications, which handle many user interactions directly and make web server requests asynchronously. As a result, Ajax applications are able to deliver a richer and more responsive user experience. Some of the best examples of this richer experience are the map applications, which enable users to pan and zoom while asynchronously retrieving needed tiles from the web server.

Ajax applications have some significant advantages over embedded applications. They can be more easily deployed and updated through the same search and access techniques used for web pages. Developing web applications is far easier too; the simplicity of the languages and tools, particularly for building connected applications, allows developers and designers to be more productive. Connected applications, or applications that leverage dynamic data or web services, are becoming the predominant form for modern applications.

The webOS application model combines the ease of development and maintenance of a web application with the deep integration available to native applications, significantly advancing the mobile user experience, while keeping application development simple.

Application Framework and OS

Through Palm's application framework, applications can embed UI widgets with sophisticated editing, navigation and display features, enabling more sophisticated application user interfaces. The framework also includes event handling, notification services and a multi-tasking model. Applications can run in the background, managing data, events and services behind the scenes while engaging the user when needed.

You can create and manage your own persistent data using HTML5 storage functions, and you can access data from some of webOS's core applications, such as Contacts and Calendar. You also have access to some basic system services, most of which are device-resident, such as Location services and Accelerometer data, along with some cloud services, such as XMPP messaging.

Architecturally, Palm webOS is an embedded Linux operating system that hosts a custom User Interface (UI) System Manager built on standard browser technology. The System Manager provides a full range of system user interface features including: navigation, application launching and lifecycle management, event management and notifications, system status, local and web searches, and rendering application HTML/CSS/JavaScript code.

You don't need to build a webOS application to make your web content accessible to webOS devices. Palm webOS has a separate browser application to handle standard web pages, and browser-based web applications. While it's expected that more and more web content and services will be delivered as webOS applications, there are millions of legacy websites and information that will continue to be presented in ways best viewed with a classic web browser. Palm webOS supports traditional web content very competitively.

Beyond the operating system, webOS includes a number of core applications: contacts, calendar, tasks, memos, phone, browser, email and messaging. Other applications are included in the initial release, such as a camera, photo viewer, audio/video player and map application, but the full application suite for a given webOS device will vary depending on the model and carrier configuration.

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Material on this page is excerpted from the O'Reilly Media book " Palm® webOS: Developing Applications in JavaScript Using the Palm MojoT Framework", ISBN 9780596155254, ©2009, by permisison of the publisher.