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diff --git a/usth/ICT2.7/P3L1 Software Architecture Subtitles/2 - Interview with Nenad Medvidovic - lang_en_vs6.srt b/usth/ICT2.7/P3L1 Software Architecture Subtitles/2 - Interview with Nenad Medvidovic - lang_en_vs6.srt deleted file mode 100644 index 40fa57c..0000000 --- a/usth/ICT2.7/P3L1 Software Architecture Subtitles/2 - Interview with Nenad Medvidovic - lang_en_vs6.srt +++ /dev/null @@ -1,499 +0,0 @@ -1 -00:00:00,220 --> 00:00:02,900 -Because the topic of today's lecture is software architecture, - -2 -00:00:02,900 --> 00:00:05,390 -it seemed appropriate to start the lesson by asking a - -3 -00:00:05,390 --> 00:00:08,960 -world expert on this topic, what is software architecture, and - -4 -00:00:08,960 --> 00:00:11,570 -why it is important. To do that, let's fly to - -5 -00:00:11,570 --> 00:00:14,910 -California, and more precisely, Los Angeles, and visit Professor - -6 -00:00:14,910 --> 00:00:19,540 -Nenad Medvidovic. Hi, I'm here visiting Professor Nenad Medvidovic from - -7 -00:00:19,540 --> 00:00:22,310 -the University of Southern California. And Neno is one of - -8 -00:00:22,310 --> 00:00:25,250 -the world experts in software architecture, actually one of the - -9 -00:00:25,250 --> 00:00:28,300 -authors of, of a recent book which is, sort of the - -10 -00:00:28,300 --> 00:00:31,660 -book in software architecture. What I would like to discuss with - -11 -00:00:31,660 --> 00:00:34,500 -Neno is the concept of software architecture and its importance. Because - -12 -00:00:34,500 --> 00:00:37,520 -people are very familiar with the idea and the cost of the - -13 -00:00:37,520 --> 00:00:41,240 -design. And software architecture is something is very related to that, - -14 -00:00:41,240 --> 00:00:43,690 -but is less known. So I would like for Nenad to - -15 -00:00:43,690 --> 00:00:46,350 -elaborate on that, and tell us why is it important to - -16 -00:00:46,350 --> 00:00:49,880 -focus also on this specific you know, architectural aspects of the software. - -17 -00:00:49,880 --> 00:00:50,380 ->> When you - -18 -00:00:50,380 --> 00:00:53,220 -build any software system, even a simple, relatively simple - -19 -00:00:53,220 --> 00:00:56,840 -one. You're going to go through, a process of making - -20 -00:00:56,840 --> 00:01:00,070 -many, many design decisions. Hundreds or thousands sometimes even tens - -21 -00:01:00,070 --> 00:01:03,140 -of thousands of design decisions, so any program that you - -22 -00:01:03,140 --> 00:01:06,090 -write at some point you get to deciding what - -23 -00:01:06,090 --> 00:01:09,385 -the interface of a particular method is going to be. - -24 -00:01:09,385 --> 00:01:12,170 -Are you're going to put in a parameter that is - -25 -00:01:12,170 --> 00:01:15,530 -an integer or a float. When you're writing your routine - -26 -00:01:15,530 --> 00:01:17,400 -about some sort you have to decide whether you're - -27 -00:01:17,400 --> 00:01:18,900 -going to use a static data structure or a - -28 -00:01:18,900 --> 00:01:22,410 -dynamic data structure. All these things are design decisions. - -29 -00:01:22,410 --> 00:01:25,770 -Many of them however, will typically, in the average - -30 -00:01:25,770 --> 00:01:29,030 -case, not really impact the success of your system - -31 -00:01:29,030 --> 00:01:31,640 -and the long term well-being of your system. But - -32 -00:01:31,640 --> 00:01:35,390 -typically the things that software engineers start struggling with - -33 -00:01:35,390 --> 00:01:40,760 -are other design decisions. Design decisions that are the equivalent - -34 -00:01:40,760 --> 00:01:42,080 -of load baring walls in a building - -35 -00:01:42,080 --> 00:01:42,660 ->> Mm hm - -36 -00:01:42,660 --> 00:01:43,950 ->> These are the things that, if you - -37 -00:01:43,950 --> 00:01:45,960 -don't get them right, or if you compromise - -38 -00:01:45,960 --> 00:01:50,190 -them, will in fact potentially impact how the - -39 -00:01:50,190 --> 00:01:54,300 -system operates. They might result in failures of different - -40 -00:01:54,300 --> 00:01:56,780 -kinds. They may result in a system that - -41 -00:01:56,780 --> 00:01:59,460 -is not easily maintainable and so forth. In - -42 -00:01:59,460 --> 00:02:01,680 -a sense, to make a long story short, - -43 -00:02:01,680 --> 00:02:05,888 -architectural design decisions are really the principle design decisions - -44 -00:02:05,888 --> 00:02:07,900 -in your system. These are the things that are - -45 -00:02:07,900 --> 00:02:10,550 -very important. All of the other design decisions you - -46 -00:02:10,550 --> 00:02:13,520 -could sort of tag with being important, but they're - -47 -00:02:13,520 --> 00:02:17,730 -sort of below this very important or highly important threshold. - -48 -00:02:17,730 --> 00:02:21,400 ->> So if you need to change a low level design decision, sometimes - -49 -00:02:21,400 --> 00:02:23,970 -it's kind of easy to do. It might change a little structure. Is it - -50 -00:02:23,970 --> 00:02:27,140 -the case that you know, being the architecture is sort of the pillar of - -51 -00:02:27,140 --> 00:02:29,020 -the software, is that going to be much - -52 -00:02:29,020 --> 00:02:32,380 -more difficult to change an architectural decision? - -53 -00:02:32,380 --> 00:02:34,400 -And architecture is deemed to be you know, - -54 -00:02:34,400 --> 00:02:36,120 -say if you start with the wrong architecture the - -55 -00:02:36,120 --> 00:02:39,510 -software is going to, you know, necessarily be unsuccessful. - -56 -00:02:39,510 --> 00:02:41,320 -Or you can also do something that is better. - -57 -00:02:41,320 --> 00:02:46,070 ->> A system could be successful and very poorly architected. Just - -58 -00:02:46,070 --> 00:02:50,630 -like a building or an airplane or a car, any other - -59 -00:02:50,630 --> 00:02:54,700 -engineering artifact could be successful but poorly architected. So success we - -60 -00:02:54,700 --> 00:02:57,440 -can separated from this, but the, the point that you make in - -61 -00:02:57,440 --> 00:03:00,530 -asking this question is an important one. The - -62 -00:03:00,530 --> 00:03:04,260 -non-architectural design decisions, should be on the - -63 -00:03:04,260 --> 00:03:06,250 -average, there are exceptions and we need to - -64 -00:03:06,250 --> 00:03:09,580 -acknowledge that there is no one size fits all - -65 -00:03:09,580 --> 00:03:11,640 -type of solution for anything in software engineering - -66 -00:03:11,640 --> 00:03:15,060 -really. But on the average, the non-architectural design decisions, - -67 -00:03:15,060 --> 00:03:17,650 -should be much easier to make. So the - -68 -00:03:17,650 --> 00:03:22,600 -scale of the consequences of making such a change. - -69 -00:03:22,600 --> 00:03:25,880 -Really can vary from very minor, highly localized - -70 -00:03:25,880 --> 00:03:29,670 -to very important and sometimes, even system wide. - -71 -00:03:29,670 --> 00:03:33,570 ->> To conclude, I just like to ask you about some concept that is - -72 -00:03:33,570 --> 00:03:35,110 -we here about a lot. Which is - -73 -00:03:35,110 --> 00:03:37,430 -architectural erosion. Since, we're talking about in with - -74 -00:03:37,430 --> 00:03:39,760 -fine architecture and software evolution. So, what is, - -75 -00:03:39,760 --> 00:03:42,090 -exactly, an architectural erosion and why does that - -76 -00:03:42,090 --> 00:03:47,600 -happen? So, to go back to our non software metaphors. Imagine you buy a car. - -77 -00:03:47,600 --> 00:03:49,810 -And your car has four wheels, it has a steering wheel, it has - -78 -00:03:49,810 --> 00:03:53,700 -a nice chassis, it looks pretty nice. At one point, you end up - -79 -00:03:53,700 --> 00:03:54,950 -replacing its 150 horsepower engine with - -80 -00:03:54,950 --> 00:03:56,800 -a 250 horsepower engine because that's what - -81 -00:03:56,800 --> 00:04:01,510 -you want. And you start putting a spoiler on the back of the car - -82 -00:04:01,510 --> 00:04:04,680 -and then you replace the headlights. And then you replace the side view - -83 -00:04:04,680 --> 00:04:08,000 -mirrors with smaller ones because you want your car to be more aerodynamic. - -84 -00:04:08,000 --> 00:04:10,620 -And then you start tinkering with other things, like you cut the, maybe - -85 -00:04:10,620 --> 00:04:13,380 -the roof of the car because you want to turn it into a convertible, - -86 -00:04:13,380 --> 00:04:15,990 -et cetera. And in the end, what you have is - -87 -00:04:15,990 --> 00:04:19,810 -a car that is still your car. Looks very different, It's - -88 -00:04:19,810 --> 00:04:23,650 -structural and behavioral properties are very different And, what you - -89 -00:04:23,650 --> 00:04:27,260 -might find is that the car doesn't handle nearly as well. - -90 -00:04:27,260 --> 00:04:29,670 -For example, in a very sharp turn it might not - -91 -00:04:29,670 --> 00:04:31,910 -be able to negotiate a steep hill as well. Because you - -92 -00:04:31,910 --> 00:04:35,760 -pretty much changed it all along the way. Architectural erosion in - -93 -00:04:35,760 --> 00:04:38,620 -the case of a software system is the exact same thing - -94 -00:04:38,620 --> 00:04:41,480 -with one huge caveat. Very few, if any of us, - -95 -00:04:41,480 --> 00:04:44,970 -will ever put a new engine into our car or tinker - -96 -00:04:44,970 --> 00:04:47,390 -with the structural soundness of the car by cutting off the - -97 -00:04:47,390 --> 00:04:50,260 -roof etc. In a software system we do it all the - -98 -00:04:50,260 --> 00:04:53,530 -time. We'll add a feature. We'll change one bit of the - -99 -00:04:53,530 --> 00:04:57,088 -user interface here. We'll port it to a new platform, some - -100 -00:04:57,088 --> 00:05:00,990 -kind of a, a mobile platform, for example. And pretty soon, - -101 -00:05:00,990 --> 00:05:03,750 -what you end up with is really a software system that, - -102 -00:05:03,750 --> 00:05:06,990 -that is maybe a distant relative of your original - -103 -00:05:06,990 --> 00:05:10,500 -system. It is a mutant in many ways, because often - -104 -00:05:10,500 --> 00:05:12,986 -times these little tinkerings happen on a one off - -105 -00:05:12,986 --> 00:05:15,610 -basis. There is no over-arching vision of how you should - -106 -00:05:15,610 --> 00:05:19,060 -do this. So, you are basically going through a - -107 -00:05:19,060 --> 00:05:21,980 -subsequent set of steps where you are making locally optimal - -108 -00:05:21,980 --> 00:05:25,240 -decisions for any one of these changes and what - -109 -00:05:25,240 --> 00:05:29,140 -you might end up finding is that the globally optimal - -110 -00:05:29,140 --> 00:05:32,100 -behavior of the system is badly compromised. The structural - -111 -00:05:32,100 --> 00:05:34,952 -soundness in a sense of the system badly compromised. - -112 -00:05:34,952 --> 00:05:38,510 -The non-functional properties of the system could be seriously - -113 -00:05:38,510 --> 00:05:42,390 -affected. This is how security flaws creep into systems. This - -114 -00:05:42,390 --> 00:05:44,250 -is how reliability flaws. This is how we use - -115 -00:05:44,250 --> 00:05:48,420 -the usability of a system often times suffers. And most - -116 -00:05:48,420 --> 00:05:50,920 -importantly for software engineers, the people who actually build the - -117 -00:05:50,920 --> 00:05:54,950 -software, the maintainability of the system becomes a huge problem. - -118 -00:05:54,950 --> 00:05:59,130 -Because now you're looking at this thing, it's got all these various appendages, - -119 -00:05:59,130 --> 00:06:03,170 -its original design has pretty badly eroded and yet somehow you have to - -120 -00:06:03,170 --> 00:06:06,850 -figure out how to keep fixing it. Making sure that it operates in - -121 -00:06:06,850 --> 00:06:11,380 -a continuous fashion because many of these systems live for 20, 30, 40 years. - -122 -00:06:11,380 --> 00:06:13,840 ->> Thank you so much for your insight; it is a perfect - -123 -00:06:13,840 --> 00:06:16,500 -introduction for our lesson. So we'll get to the lesson now. And. - -124 -00:06:16,500 --> 00:06:17,920 ->> Thank you very much. - -125 -00:06:17,920 --> 00:06:18,300 ->> Thank you. |