P4L5 Design Principles

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School

Georgia Institute Of Technology *

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Course

6310

Subject

Computer Science

Date

Oct 30, 2023

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pdf

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Uploaded by SuperElkMaster712

Design Guidelines e Design CAN'T resly be taught, but has to be learned through experience o Offered severa ways to learn from the experience of others l e Design principles are informal guidelines Design Quality » One of severa ways of gauging the quality of designs e Utimate validation of design is to build the program and have its users report their satisfaction o Can buld 8 prototype or conduct design reviews e Various metrics can compute actudl numbers assessing the quality \ « Least expensive but conceivably most valuable

Design Guidelines Coupling e also caled 8 design principle or design heuristics » Extent to which 3 module is dependent on other modules * an ipformal piece of e Coupling of your advice about the . modules should be low in structure of 8 design order to make it easier to maintain them o téke the form of * invented by Larry k do's and don'ts Constantine Cohesion Orthogonality . o Extent to which the features of a o Extent to which 8 module has 8 system can be varied independently single purpose i gie purp e Enhance the orthogonality of your system in order to « Cohesion shoud be high g:/aa'fgblfgotrg i?Spfli‘cgr;?s in order to enhance understandability and o Clarifies system promote reuse descriptions and support automatic generation e Developed by David l e Invented b.y Larry McGovern and Christopher Constantine Date

e also caled encapsulation o Extent to which the implementation details of a system are encapsulated behind abstract interfaces e Use of inheritance can Information Hiding Catalog e Give the principle's name, author, definition and implications of its use violate information hiding e Only guidelines and not e developed by David Parnas hard-and-fast rules Place the letter indicating the described design principle into the text box next to the situation describing it: A. Coupling B. Cohesion C. Orthogonality D. Information hiding B C D A Improves reusability Enables maximum variability Raises the level of adbstraction Requires more code reading

Catalog e Give the principle's name, author, definition and implications of its use e Only guidelines and not hard-and-fast rules Liskov Substitution Principle e Barbara Liskov e Subclass instances should satisfy . parent-class constraints e Implies that child class instances should obey parent class invariants \ and method contracts

Law of Demeter e Karl Lieberherr e Suggests limits on the classes that can be referred to by 8 given method o Limits the objects that can be referred to e Reduces coupling, but sometimes requires extra wrapper classes Hollywood Principle e Donald Wallace o Frameworks consist of a set of abstract classes together with rules for the ways that therr concrete subclasses may interact » Suggests that calls should be made from the framework to the client classes e also caled inversion of control \ « "Don't cal us; we'l cal you"

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