| OCR Text |
Show 12 C:emst.on<' h<'tS threC' locking ntocles: reacl , write (a ll ows oth e rs to read hu t not modify ), and exc lu sive. If lo cl: r e qU<~ sts cannot be granted , they are aborted . ( ;<'t ll SI. lltl<' S<'t·i;lli ;scs dll tUlJ<"IJI'J'Cc'll t tril tJS<IC1 io tlS a nci l!Sf'S i\.1'1 OJJfim/sL/c CUl tCU JTCIJ CY curil rol sclwml', i.e. , access conf1icts arc checked at t ra.nsactiotl cotltm iL time rather tlran at access time. It uses "shadowing" for recovery. Gemston<-~ a llow s q ueries to be performed against sets of instances of a class or dgairtst collt-:ctious of objects. T'bis c ul l<-~ ct iotl of objects can be indexed fm faste r iiCCC'SS. 2.5.4 Iris Iris [10] was developed at Hewlett-Packard Laboratories. It supports both C and LISP. Iris is built on top of Hewlctt-Pa.cka.rd's Allbase relation al DBMS. It irr krrral ly rcp rcs<'u ts objects iu tlw clatah<tse by logica l identifi ers. Tlw Iris Storage !Vlanage r is d C<l trveutioud l relat ional :-;to rag<' subsystem . It suppor ts l lw c! y narnic c:rcittion and delet ion of rela.t ions, transact ion s with "sa.vepoints" <t ttd ''r<'s1.ores to savepoin ts," conctitTett cy control , logging and re co vf~ ry , in dexin g, and bufTer rnanagement. Iris has a version control mechanism which interacts with a tran sact ion managf-' llH't tt ruechan isrn to a llow the user Lo check out orre or rnore ohject versious for <'xtendecl rnanipuLtlion. It also bas t he uotion of public and logically private <I dtab a.s <-~s . The Iris qu(-TY language extends SQL in two ways: it provides direct references to objects instead of keys and a llows functions to be called within \1\!I-IERE and SELECT clauses. |
