CMPUT 301 Lecture 02 Basic concepts of Design

CMPUT 301: Lecture 02 Basic concepts of Design and Implementations Lecturer: Martin Jagersand Department of Computing Science University of Alberta Notes based on previous courses by Ken Wong, Eleni Stroulia Zach Dodds, Martin Jagersand

Goals today: • Concepts and stages in the program designs and implementation process. • How and why Object Oriented design and Programming evolved and where it fits in the greater picture of Sw. Eng paradigms. • Some practical OO concepts and examples. 2

Design strategies overview: • Previous courses: learned pragmatics of programming and principles of algorithms • This course: Focus on whole project design. • Important concepts: – abstraction (simplifying to its essentials the description of a real-world entity) – separation (treating “what” and “how” aspects independently) 3

Abstraction • Examples: sales person, medical patient, etc. 4

Abstraction • Design strategy 1: – focus on the essential aspects of an entity or concept – ignore or conceal non-essentials – map real-world entities to software objects • Abstraction = – a named collection of attributes (data) and behavior (actions, methods) relevant to modeling a given entity for some particular purpose 5

Separation • Design strategy 2: – separate “what” is to be done from “how” it is done – separate design issues from implementation details – separate externally “visible” behavior (interfaces) from hidden, internal mechanisms (implementations) 6

Interchangeable Implementations 7

Interchangeable Implementations 8

Separation • Separation of concerns: – interfaces reveal assumptions – implementations hide changeable details – interface == contract – avoid ripple effects 9

Design concepts vs. programming languages • Note that design concepts (e. g. abstraction, separation …) are independent of programming languages • But one or several programming language may support or impose certain concepts. Example: Separation: –. h files in c – Definition modules in modula 2, 3 – Interfaces in java 10

Programming languages • Programming paradigms and languages are between (and link) human concepts and ideas to machine implementations • Have changed during time (more so than either ideas or machines) Prog. Lang. Computer Human ideas 11

Evolution of programming languages • • • Machine lang Imperative (Fortran, c, Pascal…) Functional (lisp, ML, Haskell…) Logical (prolog, alf…) Object Oriented (Smalltalk, c++, java) 12

Design Strategies vs. programming languages • Note again that design strategy (e. g. abstraction, separation …) are independent of programming languages. • Also: The same project can be implemented using different strategies (and languages) 13

Example: Higher order functions • Concept from functional design paradigms and mathematics • Q=f g • Implementation in imperative and OO languages and comments. (blackboard) 14

Example: XVision • Provides visual tracking (rmember interaction video in last lecture) • 10+ years effort several people, several univ • Several implementations, same functionality • Xvision 1 -1. 3 (Upenn, Yale): c, c++, Imperative • f. Vision (Yale): Haskell, greencard, c • XVision 2 (JHU): c++ (Written using some fvision design strat) 15

Xvision application: face tracking 16

Xvision 1 -1. 3 (Upenn, Yale): c, c++, Imperative • Written by “hackers” • Neat tricks speed up, but shortcut across abstractions • Good to provide specified functionality, • but hard to port • Hard to extend 17

f. Vision (Yale): Haskell, greencard, c Example program: track. Mouth v = best. SSD mouth. Ims (newsrc. I v (sizeof mouth. Ims)) track. LEye v = best. SSD leye. Ims (newsrc. I v (sizeof leye. Ims)) track. REye v = best. SSD reye. Ims (newsrc. I v (sizeof reye. Ims)) track. Eyes v = composite 2 (split, join) (track. LEye v) (track. REye v) where split = seg. To. Oriented. Pts --- some geometry join = oriented. Pts. To. Seg --- some more geometry track. Clown v = composite 2 concat 2 (track. Eyes v) (track. Mouth v) 18

f. Vision (Yale): Haskell, greencard, c • • • Uses dataflow model, higher order functions Much easier to script new behaviours Easier to express geometry More compact code Haskell code about speed: about ¼ of c 19

XVision 2 (JHU): c++ • • See it in our lab, use in c 306, learn in c 610! Designed first, then implemented Extensible, portable Some loss of “neat” speadups due to separation and hiding • Speed: ¼ - 1/7 of original c version. 20

Next time: • Object oriented design strategies 21