Collections Principle 4: A good collection is broadly available and avoids unnecessary impediments to use. 

This principle encompasses three attributes: availability, usability, and accessibility. 

Availability means that the collection is accessible and usable upon demand by an authorized  person. This implies that collections should be accessible through the Web, using technologies  that are well known among the target user community. They should be “up” as close to 24/7 as  possible, which has implications for system security and maintenance. Availability does not  require that use of all materials be free and unrestricted; charging for use and limiting access  may be appropriate and even necessary in some circumstances. But it does require an attempt to  make the materials as widely available as possible within any required constraints. 

• American Library Association, Principles for Digital Content (2007) http://www.ala.org/ala/washoff/oitp/Principlesfinalfinal.pdf. These recently adopted  principles emphasize commitment to equitable access.  

Usability refers to ease of use. There is often a tradeoff between functionality and general  usability; the timing of the adoption of new features should be considered in light of how many  potential users will be capable of using the technology and how many will find it a barrier.  Bandwidth requirements are also a consideration, as some file formats or interfaces may not be  usable by individuals on low bandwidth connections. The minimum browser version and  bandwidth requirements for use should be documented as part of the collection description. 

For general access collections, the web pages and search forms providing access to the  collection, as well as the metadata and digital object displays, should be tested against various  browsers and browser versions. Different operating systems support different commands for  manipulating screen information, such as selecting multiple items in a drop down menu on a  search screen, so testing should include Windows, Mac, and Linux operating systems for at  least the current and previous three years. Testing should include different screen resolutions  (varying height and width pixel arrays). Look for particularly problematic items, such as color  variations, display of non-English language characters, and rendition of XML. 

• Usability.gov website http://www.usability.gov/. An excellent source of information on  usability and user-centered design for websites and other communication systems.  
• U.S. Department of Health and Human Services, Research-Based Web Design & Usability Guidelines – Current Research-Based Guidelines on Web Design and Usability Issues (2006) http://www.usability.gov/pdfs/guidelines.html.   
• Technical Advisory Service for Images (TASI), Developing Effective Interfaces for Online  Image Collections (2006) http://www.tasi.ac.uk/advice/delivering/interfaces.html.  
• Technical Advisory Service for Images (TASI), Developing Usable and Accessible Interfaces  for Online Image Collections (2006) http://www.tasi.ac.uk/advice/delivering/usability.html.  

Accessibility is the property of being usable by people with disabilities. Collection interfaces  should be designed to maximize usability for people with visual impairments, loss of hearing,  loss of mobility (for example, trouble using a mouse) and even cognitive impairments. 

Legislation and de facto standards define web accessibility: 

• World Wide Web Consortium (W3C), Web Accessibility Initiative (WAI) website http://www.w3.org/WAI/. The most important single site for accessibility issues. Includes links to W3C accessibility standards.  
• W3C Web Accesssibility Initiative, Policies Relating to Web Accessibility website http://www.w3.org/WAI/Policy/. Links to accessibility legislation in 17 countries plus the United Kingdom and European Union.  

Several clearinghouses focus on web accessibility, among them: 

• CPB/WGBH National Center for Accessible Media website http://ncam.wgbh.org/projects/.  Includes a number of accessibility initiatives including projects focused on educational  materials.  
• University of Wisconsin, Trace Research and Development Center: Designing More UsableWeb Sites http://trace.wisc.edu/world/web/. A clearinghouse of useful tools, initiatives, and  documentation on accessibility.  

There is a large body of literature on accessible web design: 

• Utah State University Center for Persons with Disabilities, WebAIM (Web Accessibility in Mind) website http://www.webaim.org/. An excellent introduction to Web accessibility issues and evaluation tools.  
• Massachusetts Institute of Technology, Adaptive Technology for Information and Computing website http://web.mit.edu/atic/www/accessibility/index.html. Shows how accessibility guidelines can be applied in an institutional context.  
• Audio Illinois website http://www.alsaudioillinois.net/. A model site using audio narration to describe pictures for the sight impaired.