John is a developer in charge of designing and deploying a new mobile web site. As a requirement the site must be accesible from a myriad of devices including mobile phones, smartphones and different kind of PDAs (Palm, Blackberry, Pocket PC). The customer is expecting a good experience in all the devices addressed, exploiting all device features at a maximum.

There are some requirements that has to do with the presentation of different information in tabular format. Initially John starts designing all the tables to have only two columns, restricting the amount of information of each entity to the two most important data fields. This design is suitable for the majority of mobile phones but when he tests on a PDA device, John realizes that two columns provide a very poor result on a PDA device. He realizes that space is wasted and decides to add an additional column that will be only displayed for those devices that are PDAs.

To overcome that issue, John creates a new device family called 'PDADevice' using a tool provided by a W3C-compliant device description solution. This family of devices will be characterized by a set conditions on the device capabilities, such as screen dimensions, supported markup code, available memory, etc. Once the device family is created and uploaded to the DDR, John uses the DDR API in his favourite programming language to generate the markup table accordingly to the established requirements.

Company A wants to develop a new mobile web application and would like to provide different layout and content to different groups of devices. As company A doesn't like reinventing the wheel, instead of creating a new device family, queries the DDR, and realizes that there is a device family that suits its needs as defined by company B who is working in the same space. Company A can consistently reuse that family of devices and references it in his own application.

It is common to hear names such as "Smartphone", "Musicphone", "Featurephone", but does anyone know what they mean in detail? Is a Smartphone a device to make calls, synchronize your calendar and provide a fully featured address book? If so, what is the difference between a Smartphone and a PDA? When does a mobile phone "turn" into a Smartphone? When isn't it a Smartphone anymore and become a PDA?

All these definitions are very important to many individuals and companies. Providing a way to define clearly {*} and formally what they are will help comunication between different individuals and companies.

When developing an application, for J2ME, Symbian etc, it is often useful to create different builds for different devices or use different API's to exploit the device capabilities, namely 3D hardware acceleration, stereo speakers, bluetooth chips, GPS support and more. In order to do this, developers might have to create one build for each device on the market. Many devices actually share the same functionalities and support the same API's. Developing and testing on a device often means supporting a range of devices. Companies in this space will claim compatibility with device families instead of individual devices.

An specific instantiation of this use case, relevant to the Mobile Web, is a mobile web browser vendor who wants to express the fact that their browser works in a set of devices. For example, "our MiniBrowser is compatible with all Nokia Series 60 devices".

Company A is a developer of J2ME applications. Every month its QA team tests the new games against the devices they have in their lab. Devices used for testing are often considered master devices representing a number of other devices that will not be tested directly. Also, every month, the company lab buys new devices, old games are tested against these devices for compatibility. Company A states formally on which devices and device families their games work on.

Company B is a content aggregator. Every month receives from different software developers a number of new games. Company B also keeps updates of their device database so every month new devices are added. Every month Company A sends to Company B a list of the games and a list of the devices and group of devices (families) compatible with the games provided.

Company B needs to go back and check the list of devices and games every month for each of the games. The ability of using a common representation of device families between Company B and each of its affiliate games developers would ease the work on a daily basis and make sure that all the devices that are certified to work with a certain game are up-to-date. For example, if Company B has a brand new device in its database and that device belongs to a device family certified by Company A, Company B can automatically state that a certain game works in that new device.

It is the element that serves as root of the XML document

This element is the parent element for all the vocabulary declarations in the XML document.

The purpose of this element is the declaration of the vocabularies that will be used in the group definitions.

This element is the parent element for all the groups defined

This is the element used to define a group of devices

This element includes the boolean expression that defines a group.

At initialization time the user of the API need to pass the XML file with the group definitions to be used. This can be used passing the XML file as an additional initialization property.

Returns true if a device belongs to a group

public boolean belongsTo(Evidence evidence,String group);