]> 'I' [ '2'..'9' | '1'..'9' { '0'..'9' }+ ] [ 'I' [ '2'..'9' | '1'..'9' { '0'..'9' }+ ] { ", " 'I' [ '2'..'9' | '1'..'9' { '0'..'9' }+ ] }* ] { $letter | '_' }+ { ! $letter $anyCharacter }* $letter { $anyCharacter }* [ 'R' '1'..'9' { '0'..'9' }* { ", " 'R' '1'..'9' { '0'..'9' }* }* ] 'R' '1'..'9' { '0'..'9' }* The following definition is taken from <a href="../../../../References.html#OOA91">[OOA91]</a>: <blockquote> Definition. "An <i>object</i> is an abstraction of a set of real-world things such that <ul> <li>all the things in the set&#8212;the instances&#8212;have the same characteristics, and</li> <li>all instances are subject to and conform to the same set of rules and policies."</li> </ul> </blockquote> The following definition is taken from <a href="../../../../References.html#OOA91">[OOA91]</a>: <blockquote> "Definition. An <i>attribute</i> is an abstraction of a single characteristic possessed by all entities that were themselves abstracted as an object." </blockquote> The following definition is taken from <a href="../../../../References.html#OOA91">[OOA91]</a>: <blockquote> Definition. "An <i>identifier</i> is a set of one or more attributes whose values uniquely distinguish each instance of an object." </blockquote> R139 = (R138 + R115 + R116) - R137