A　basic　premise　of　OGSA　is　that　everything　is(66)by　a　service:　a　network　enabledentity　that(67)some　capability　through　the　exchange　of　messages.　Computational　resources,　storage　resources,　networks,　programs,　databases,　and　so　forth　are　all(68).　This　adoption　of　auniform.　service-oriented　model　means　that　all　components　of　the　environment　are　virtual.　Morespecifically,　OGSA　represents　everything　as　a　Grid　service:　a　Web　service　that　conforms(69)a　set　of　conventions　and　supports　standard　interfaces　for　such　purposes　as　lifetime　management.　This　core　set　of　consistent　interfaces,　from　which　all　Grid　services　are　implemented.(70)the　construction　of　hierarchical,　higher　-　order　services　that　can　be　treated　in　a　uniform.　way　across　layers　of　abstraction.