Towards a unified definition of web accessibility
Helen Petrie, Andreas Savva, Christopher Power · 2015 · Proceedings of the 12th International Web for All Conference (W4A) · doi:10.1145/2745555.2746653
Summary
This paper conducts a systematic conceptual analysis of 50 definitions of web accessibility drawn from books, academic papers, standards documents, guidelines, and online sources spanning 1996 to 2014, authored by researchers and practitioners from 21 countries across all continents except Africa. The goal is to identify what the research and practitioner communities consider to be the core components of web accessibility and to propose a unified definition that synthesizes these perspectives. The authors extracted relevant content words from each definition, grouped synonyms and grammatical variations, then clustered the terms into concepts. Six core concepts emerged from this analysis: (1) groups of users and their characteristics (mentioned in 98% of definitions), (2) what users should be able to do with websites (88%), (3) technologies used including mainstream and assistive technologies (30%), (4) usability characteristics of the website (30%), (5) design and development processes (24%), and (6) contexts of use (14%). The paper visualizes these concepts as concentric layers in an "onion diagram," with the most frequently referenced concepts at the centre. The authors also traced the antecedents of each definition, finding that only 24% of authors explicitly referenced previous definitions when proposing their own, making it difficult to track how the concept has evolved.
Key findings
The analysis reveals significant inconsistency in how web accessibility is defined. While nearly all definitions (98%) reference user groups — most commonly people with disabilities (70%) — only three of the 50 definitions explicitly mentioned older users, despite this group being widely acknowledged in the field. A striking 40% of definitions were circular, defining accessibility merely in terms of "access." The WAI definition ("people with disabilities can perceive, understand, navigate and interact with the Web") was the most popular among surveyed practitioners (45%), followed by the Section 508 definition (32%). The proposed unified definition synthesizes all six concepts: "all people, particularly disabled and older people, can use websites in a range of contexts of use, including mainstream and assistive technologies; to achieve this, websites need to be designed and developed to support usability across these contexts." Notably, only 30% of definitions mentioned the relationship between accessibility and usability, despite this being a foundational connection that shapes how accessibility is measured and evaluated.
Relevance
This paper addresses a fundamental problem for the accessibility field: without a shared definition, researchers cannot meaningfully compare studies, practitioners lack a complete framework for evaluating their work, and important dimensions of accessibility risk being overlooked. The unified definition is valuable because it explicitly connects accessibility to usability — framing accessible design not just as removing barriers but as achieving usability across diverse contexts and technologies. The near-absence of older users from most definitions is a significant finding, given aging populations worldwide. For practitioners, the six-concept framework provides a useful checklist: does your accessibility work consider all user groups, what they need to do, the technologies they use, usability qualities, design processes, and contexts of use? The "onion diagram" visualization is a practical tool for communicating accessibility's multi-layered nature to stakeholders who may hold overly narrow definitions focused solely on WCAG compliance.
Tags: web accessibility · accessibility definitions · usability · assistive technology · older users · universal design · accessibility standards
Standards referenced: WCAG 2.0 · Section 508 · ISO 9241-171 · BS 8788:2010