Models to be supported in the GPII

Picture of 4 models. Click on the picture for larger view and a long text description of the image. Function description included on this page.

The GPII will support a number different delivery models in order to address the different platforms, degrees of lockdown, and type of adaptation a person requires. For example a person who is blind may need a screen reader that is integrally tied to a browser (Model 1 or 4) while someone who has colorblindness may only need occasional color shifting of content and could use Model 2 or 3. Any of the 4 models might be used on a computer that allows installation of access software while Models 3 or 4 may be needed on a computer that is completely locked down.

Model 1: User agent based solutions.

Access solutions under Model 1 are installed and run on the user's computer. This includes:

  • access features built into the operating systems or browsers (platforms),
  • downloadable add-ons to platforms,
  • and commercial assistive technologies that are installed on a computer.

The FireVox and LowBrowse plug-ins to Mozilla Firefox are examples of Model 1. AT that runs in combination with browsers would be another example. The IBM Home Page Reader would be an older example of this approach.

This model takes advantage of the client computer's processing power in order to create faster response than server-based solutions. Additionally, these types of projects are currently the easiest to develop and deploy (especially the browser add-ons), since they require no added server side infrastructure. However, they require that users have permission to install and modify programs on every computer on which they may need access.

NOTE: Work is ongoing on a special tool that would allow some downloadable agents to be run on a computer without installation to the disk. This approach is under development and would work on some operating systems. It will not likely work on a heavily locked down system however without cooperation from the system.

Model 2: On-Demand Web Services

Model 2 represents web services that provide transformations on demand. DocAccess (which converts page images to text on demand) is an example of this approach.

These services may be called automatically from content, by a user, or by other web services. The web services perform conversions on web content that is sent to them and then return it to the user. For example, they may translate images of text into accessible text, shift colors to accomodate a specific type of colorblindness, or convert text into audio. Because these services are hosted on a remote server, they have access to processing power beyond that of the host machine. They can be used without any downloads or installation or they may require a plug in to invoke the service.

Model 3: Proxy-based transcoding

Model 3 represents proxy services that sit between the user and the content and interpret or modify its presentation on its way to the user.

These solutions require some configuration by the user to allow content to pass through the proxy gateway, so the user must have permission to modify internet settings on his computer. After initial setup, however, the user may browse normally and automatically receive pages as modified by the proxy. There are limitations to they types of content this approach can currently handle. For example it creates problems for secure socket layer (SSL) connections and may not work with some types of dynamic, interactive content. There have also been copyright issues raised in connection with this approach.

Model 4: Web-based user agents

Model 4 projects include web-based access technologies that can be used anywhere, from any internet-enabled device. WebAnywhere is an example of this approach.

With this approach processing is done at a remote server, accessed through a specified URL, and does not involve any downloads or installation at the user's computer. Because these solutions reside on the server instead of the user's computer, personalized settings can be retrieved wherever the user logs in. This approach is particularly effective for individuals without resources who often are accessing the web through other people's computer such as libraries, or community centers.


It is possible to have solutions that involve aspects of all these approaches. This can take advantage of the strengths of the different approaches will avoiding some of their limitations. The 4 Models are useful in thinking about and discussing solution approaches but the are not the only approaches and comprehensive solutions for a user are rarely pure implementations of one of the approaches.