Bartle, Richard A. <br/><br/>
Designing virtual worlds / 
Richard A. Bartle 
 - Indianapolis, IND:  New Riders,   2004 
 - xxi, 741 p.:   ill.;   23 cm. 
<br/><br/>Includes bibliographical references and index 
<br/><br/><label>ISBN: </label>0131018167 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Human--Computer interaction<br/>Computer games--Programming<br/>Computer games--Design<br/>Virtual reality--Social aspects