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This document explains the AccessForAll accessibility framework. The intended audience of this document is anyone interested in accessibility and standards, especially those from the metadata community. A small proficiency in software design is assumed from the reader (for this document uses UML in some of its explanations), however the hope is that the concepts are explained clearly enough to be understood by readers of any technical skill-level.
AccessForAll is a framework designed to define and describe resource accessibility. Its goal is to provide a means whereby resources are matched to the accessibility preferences expressed within an individual preference set. The framework is divided into the following concepts, which, when used in conjunction, make possible the matching of resources to preference sets and the description of resource accessibility:
adaptation preference and property
These concepts and their interaction will be discussed further in this document, alongside the presentation of the AccessForAll abstract model.
The concepts behind the AccessForAll framework were originally developed by the IMS Accessibility Working Group1. The working group defined two specifications: the IMS Accessibility for Learner Information Package (AccLIP) and the IMS AccessForAll Meta-data [sp] Specification (AccMD). Together they defined what is currently the AccessForAll framework in an applied, XML-specific way. This document hopes to explain the main concepts behind the AccLIP and AccMD, i.e. the AccessForAll framework, in an abstract way.
This section specifies an abstract model for the AccessForAll framework. The primary purpose of this section is to provide a reference model against which particular metadata encodings can be written.
The abstract model of the preference sets defined in the AccessForAll framework is as follows:
Each preference set has zero or more required access modes.
Each preference set has zero or more prohibited access modes.
Each preference set has zero or more adaptation preference / value pairs.
The abstract model of the resources defined in the AccessForAll framework is as follows:
Each resource has one or more access modes2.
Each resource may be related to zero or more alternative resources.
Each resource has zero or more adaptation property / value pairs.
Each adaptation property matches an adaptation preference.
Each adaptation property value / pair may contain access mode information.
Each resource conforms to zero or more standards.
The AccessForAll abstract model for resources and recods is represented as a UML class diagram in the following illustration:
Readers not familiar with UML class diagrams should note that lines ending in a block-arrow should be read as 'is' or 'is a' (for example, 'a required access mode is an access mode ') and that lines starting with a block-diamond should be read as 'contains a' or 'has a' (for example, 'an adaptation property / value pair has a value and a property'). Other relationships are labeled appropriately3.
An access mode is the human sense or medium though which a user receives the output of a resource. The mode refers to either the perceptual system, or the cognitive faculty engaged by the user. An access mode is defined either as a sense, to reference a perceptual system, or as a medium to connect with a cognitive ability. Some examples will clarify:
Describing a resource's access mode as visual implies that a user will use their visual system to process it. Pictorial and video resources are examples of such resources.
Describing a resource's access mode as textual implies that a user will rely on their ability to read in order to understand the resource's content4.
An alternative resource is the same intellectual content of the referenced resource, but presented in another access mode.
An adaptation preference states how a user desires to access a resource. In effect, it defines how a resource should be adapted in order to provide adequate means of access to a user. An adaptation property is a statement describing characteristics of the resource that affect how it can be sensed, understood, or interacted with by users or agents5. The two share a reflexive relationship in that an adaptation property matches an adaptation preference.
A reference to an established standard to which the resource conforms6.
A user is able to state his/her required and prohibited access modes. In this way a user can state what he/she wants and what he/she does not want for an access mode. In addition to this for each required, prohibited, or combination of required and prohibited access modes, a user is able to state his/her adaptation preferences. Adaptation preferences may qualify the required and prohibited access modes with information about the adaptation characteristics of the resources the user wishes to interact with, however they may also stand alone.
A resource declares its access mode(s). A resource may be an alternative to another resource and another resource may be an alternative to it. In addition to its access mode(s), a resource states its adaptation properties. A resource may conform to a number of standards.
The goal of the AccessForAll framework is to match resources to preference sets. The following is a list of guidelines for matching resources to preference sets:
A resource or alternative resource's access mode is the same as the preference set's required access mode.
A resource or alternative resource's access mode is not the same as the preference set's prohibited access mode.
A resource or alternative resource's adaptation properties match the preference set's adaptation preferences.
A resource or alternative resource's adaptation property values are the same as the preference set's adaptation preference values.
A resource or alternative resource conforms to a standard that satisfies the preference set's adaptation preferences and values. [Editorial Note : This statement needs further explanation.]
The Web Content Accessibility Guidelines (WCAG) are a set of principles and guidelines that define and explain the "requirements for making Web-based information and applications accessible to a wide range of people with disabilities7." The WCAG does not define new technologies, but rather techniques that can be applied to any type of Web content. The AccessForAll framework defines a different approach to resource accessibility, however one that complements the WCAG: The AccessForAll Framework states (via metadata on resources) the accessibility properties that are recommended by the WCAG. This enables the AccessForAll Framework a means whereby resources can be matched to the accessibility preferences expressed within an individual preference set.
David Weinkauf, Adaptive Technology Resource Centre, University of Toronto, Canada
Joseph Scheuhammer, Adaptive Technology Resource Centre, University of Toronto, Canada
Anastasia Cheetham, Adaptive Technology Resource Centre, University of Toronto, Canada
Martyn Cooper, Accessibility in Educational Media Team, Institute of Educational Technology, Open Univerity, UK
Andy Heath, Sheffield-Hallam University, UK
Liddy Nevile, Computer Science Department, La Trobe University, Australia
Madeleine Rothberg, WGBH-National Center for Accessible Media, USA
Jutta Treviranus, Faculty of Information Sciences, University of Toronto, Canada
1 The Website for the IMS Accessibility Working Group is located at http://www.imsglobal.org/accessibility.
2 We acknowledge that declaring mandatory properties on a resource is unrealistic for most metadata practices, however the compulsory nature of access modes as properties of resources is true in reality, and is thus reflected as such in the abstract model.
3 UML explanation from the DCMI abstract model (http://www.dublincore.org/documents/abstract-model/).
4 Textual content may be rendered into speech or Braille by a processing system, however these would not be considered the resource's (original) access modes.
5 Current definition of the proposed Dublin Core Adaptation term (http://dublincore.org/accessibilitywiki/NewElementProposal).
6 Definition of the Dublin Core conformsTo element refinement (http://www.dublincore.org/documents/usageguide/qualifiers.shtml#conformsTo).
7 From the Web Content Accessibility Guidelines 2.0 (http://www.w3.org/TR/WCAG20/).
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