| OCR Text |
Show 19 1. read-write conflict (pessimistic) - This prevents a read lo ck from being grant ed on an object which has been granted a writeintent lock for another c lient . 2. no-read-write conflict ( opti rn ist ic) -- This a llows a read lock on an object wh ich has bf~eu granted a WTit eirdent lock for another client. Ontos queues lock requests and r a ises an exception on lock or access conflicts. All concurrent transactions are ser iali zed . Ontos aJso supports nested transactions. (),,tns has its own object SQL in wh ich p rocedures can be called within a. query st a1,e n1 ent and direct refe rences itt obj ects can be chain ed to any dept h. These qtwJws CdJJ lw <' X t'( 11 Lcd agaiu st t he set of a.ll in stances of a class a nd aggregate o hj cc Is. 2.5.10 Orion Orion [1:3] was developed by the Advanced Computer Technology Program at IV!icroelectronics <lllcl Contputer Tecll!lology Corporat ion. It was cleve lup ecl as a research vehicle for integ ration of object-oriented progrannning languages and claL<tbases for applicatiuus such as in Al, CAD/ CAM, and office information system. lrnpleme nted in Common LJSP, the system supports int erfaces to LISP and C. The OIDs in Orion consist of <class-ic!, instan ce-id> pairs, called UIDs (Unique Identifiers) . Objects have different storage formats in memory and on disk. This llH' <'l llS t hat Uw s1urage lll a ll ap;c-r !lli JSt cc)JJvcrt hetwec11 t he two formats. increasi ng mt'rll('dd. Tlw object b11ller manager rnainta.in s a resi dent obj ect tab le (ROT) whi ch ccllltains object \JJDs ar1d a corresponding Resid e nt Object D f~scr iptor (ROD) . The ROD conta iJJS information like the obj ect's UID, its physical lo cation on disk, locks, etc. Orion a llows a.ll in stances of a c la ss to be clustered on disk for fast retrieval. It also a llows a coll ect ion of ohjt~ct s to br' kept contiguou sly on the sante disk segmen t . |
