INFS1603 Lecture Notes - Lecture 11: Relational Model, Query Language, Relational Calculus

• School: UNSW, UNSW Sydney
• Department: Information Systems
• Course: INFS1603
• Professor: All

Document Summary

Overriding: the process of replacing a method inherited from a superclass by a more specific implementation of that method in a subclass. Extensions: add to the operation: restriction: limit the operation, optimizations: improve the operation. Lea(cid:448)i(cid:374)g a fu(cid:374)(cid:272)tio(cid:374) (cid:858)(cid:271)la(cid:374)k(cid:859) (cid:373)ea(cid:374)s usi(cid:374)g the default, (cid:858)(cid:396)e(cid:449)(cid:396)iti(cid:374)g(cid:859) it (cid:373)ea(cid:374)s (cid:449)e a(cid:396)e (cid:272)ha(cid:374)gi(cid:374)g it. E. g. the (cid:858)(cid:396)e(cid:448)ie(cid:449)- appl(cid:374) (cid:894)(cid:895)(cid:859) is (cid:396)e(cid:449)(cid:396)itte(cid:374) i(cid:374) the g(cid:396)aduate stude(cid:374)t a(cid:374)d u(cid:374)de(cid:396)g(cid:396)ad stude(cid:374)t su(cid:271)(cid:272)lasses. Composition: implies a relationship where the child object cannot exist independently of the parent object. Composition is represented with a solid diamond at the composed end. An object diagram is a (concrete) instance of the (abstract) class diagram. Polymorphism: the ability of an operation to be applied to many classes. Sell, operation: calcprofitorloss might be working differently from buy, operation: calcprofitorloss. That is, the operation has the same name but might be implemented in different ways. The oo design approach provides both the data identification and the procedures or data manipulation to be performed.