| OCR Text |
Show 4 p<'rsist<'tlt data. This nwans tha.t r<'latccl data tl<~<~cls to be a llocated on second<:try storag<' iu a manner that allows for efficient access. 2.2 Why OODBMS? OODBMSs combine t he features of object-ori ented programs (OOPs) and database management systems. The c lasses and obj ects in an OOP can represent real world des igu e ntities much Lwtt <~ r tba.u flat tab les as in an RDBMS. In an OOP, it is pussible to associat<j functions with data; inheri tance a llows the data schema to be wdl structured ; finall y, p roblems like no rmalizat ion and unnecessary dupli cation of data. t hat occur in RDBI\IIS are easier to avoid in OODBMS. There a re a lso many prob lems in manipulating data. f rom inside a p rogramming language in an RDBMS. Tltis is Lwcau::w of' the fo llowing two lllismatclws: l . The data m<:-tniptila.t ion languag<., is a declarative language as opposed to the app li cation language which is imperative. 2. The p rogramming la nguage typ es have a diffe rent representat ion t han the database types. At tot her maJor draw back of t be re lat ion a l database model is that it is valuebased. As a resu lt , the re l<:d;ion slt ip betweeu two e nt it ies bas to be obtain ed by embedding the same value in hoth and performing a combining opera ti on called a ·'join." Object-oriented databases, on the other han d , a re identity based , i. e. , each obj<'d ltas an id ent ifier. This facilitates shari ng by having references fron1 various objects to the S(),!1Je object. This avoids data duplicat iou aud associated problems. l{<'latt>d e ntities in a rel at ional database have to be obtained by performing expett s ive joins whereas in OODBMS, data access is t hrough in ter-obj ect refe rences vv bi cb is mnch more efficient. |
