▁grid ▁while ▁providing ▁users ▁quick ▁access ▁to ▁the ▁datasets ▁and ▁files . ▁There ▁is ▁a ▁number ▁of ▁concepts ▁and ▁tools ▁that ▁must ▁be ▁available ▁to ▁make ▁a ▁data ▁grid ▁operation ally ▁vi able . ▁However , ▁at ▁the ▁same ▁time ▁not ▁all ▁data ▁gr ids ▁require ▁the ▁same ▁capabilities ▁and ▁services ▁because ▁of ▁differences ▁in ▁access ▁requirements , ▁security ▁and ▁location ▁of ▁resources ▁in ▁comparison ▁to ▁users . ▁In ▁any ▁case , ▁most ▁data ▁gr ids ▁will ▁have ▁similar ▁middle ware ▁services ▁that ▁provide ▁for ▁a ▁universal ▁name ▁space , ▁data ▁transport ▁service , ▁data ▁access ▁service , ▁data ▁rep lication ▁and ▁resource ▁management ▁service . ▁When ▁taken ▁together , ▁they ▁are ▁key ▁to ▁the ▁data ▁gr ids ▁functional ▁capabilities . ▁ ▁Universal ▁namespace ▁Since ▁sources ▁of ▁data ▁within ▁the ▁data ▁grid ▁will ▁consist ▁of ▁data ▁from ▁multiple ▁separate ▁systems ▁and ▁networks ▁using ▁different ▁file ▁naming ▁convent ions , ▁it ▁would ▁be ▁difficult ▁for ▁a ▁user ▁to ▁locate ▁data ▁within ▁the ▁data ▁grid ▁and ▁know ▁they ▁retrieved ▁what ▁they ▁needed ▁based ▁sole ly ▁on ▁existing ▁physical ▁file ▁names ▁( PF N s ). ▁A ▁universal ▁or ▁un ified ▁name ▁space ▁makes ▁it ▁possible ▁to ▁create ▁logical ▁file ▁names ▁( L F N s ) ▁that ▁can ▁be ▁referenced ▁within ▁the ▁data ▁grid ▁that ▁map ▁to ▁P F N s . ▁When ▁an ▁L F N ▁is ▁requested ▁or ▁quer ied , ▁all ▁matching ▁P F N s ▁are ▁returned ▁to ▁include ▁possible ▁rep lic as ▁of ▁the ▁requested ▁data . ▁The ▁end ▁user