FAANG System Design Interview: Design A Location Based Service (Yelp, Google Places)

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  • Опубликовано: 24 дек 2024

Комментарии • 400

  • @ByteByteGo
    @ByteByteGo  2 года назад +315

    Corrections: In the geohash length to grid size mapping table at 15:30 and 20:01, the correct values for 7, 8, 9 and 10 are:
    7 152.9m × 152.4m
    8 38.2m × 19m
    9 4.8m × 4.8m
    10 1.2m × 59.5cm

    • @RahulSingh-ln7bg
      @RahulSingh-ln7bg 2 года назад +8

      Hi Alex, I think you need to correct the definition, at 14:00 onwards you are talking about quadtree, not Geohash, Geohash divides the grid initially into 32 smaller grids since the base here is 32. You may like to correct it.

    • @aaditkamat4995
      @aaditkamat4995 2 года назад +2

      No wonder, that is why I was thinking why the values are considered too small when in fact they are in the ballpark of 4, 5, 6.

    • @kalmyk
      @kalmyk 2 года назад +2

      Yeah, that was confusing I had to double check

    • @Penly11
      @Penly11 9 месяцев назад +1

      In the video Sahn says that a database in the terabyte range is on the borderline where sharding might make sense. He also says that our read qps of 5,000 is quite high. I was wondering how he came to these conclusions and if there are specific numbers he looks for to determine if a number is high enough to warrant a design change?

    • @lameshithead
      @lameshithead 8 месяцев назад

      even though its quite some time since i dealed with geoinformatics, i think you orgot/mixed up some points here. first of all: how do we retrieve the data and how is it stored? when it comes to osm you can get the data in a lot of diferent ways, but you always end up in using quadtree/knearest/bruteforce, but that leads us to the next question: are the searchalgos clientside? and if not, why dont we replace those searchalgos alltogether by storing data in a different way? third: what kind of transformation are we using here? most likely datums i guess, but using the one with the letters in the rows, would make the answer go in a complete different way, than equatorial and easting, or datums without eastings

  • @zachgoll
    @zachgoll Год назад +185

    Hey RUclips algorithm, if you’re reading this, I just want to say, this is the type of video you should be recommending to software people. K thanks

  • @pramodpotdar5416
    @pramodpotdar5416 2 года назад +80

    this video is a FLOW. Could not stop watching... Beautiful animation and narration. Perfect

  • @prashanttoxeed
    @prashanttoxeed 2 года назад +322

    Best design video ever. I am so happy that Alex decided to make videos.

  • @miale3593
    @miale3593 2 года назад +149

    So much effort spent in how to make this video so informative, well structured, precisely explained and amazingly illustrated. Thank you for sharing this with us!

  • @TheTacoReview
    @TheTacoReview 10 месяцев назад +3

    Holy crap... finally a guy that actually knows what he's talking about. I've been doing this for 20 + years and this is how it's done. Kids you don't need to make it overly complex, just build it so it can scale not at scale.

  • @emreboga
    @emreboga 2 года назад +6

    Dude, your content is gold! I've been coding almost 20 years and prepared for interviews countless times. This has been one of the best content so far!

    • @ByteByteGo
      @ByteByteGo  2 года назад +11

      Thank you for the encouragement. This is the first chapter-length video we made, and it was a lot of work. Your feedback is much apprecated.

    • @ChrisCox-wv7oo
      @ChrisCox-wv7oo 2 года назад

      @@ByteByteGo wonderful job.

  • @vskovzgird
    @vskovzgird 2 года назад +41

    Hey, Alex. I learn x100 times more from this video than from my past year in IT. Totally awesome content!

  • @pizzatime9565
    @pizzatime9565 Год назад +12

    We need more full system design videos like this one from you!

  • @geeklogbook
    @geeklogbook 2 года назад +5

    This video should be taught at universities and bootcamps. Not only for the interesting topic but also to learn how to think about this kind of problem and system design in general. Thank you!

  • @mallipooalwa9085
    @mallipooalwa9085 2 года назад +8

    Wow, I'm an enterprise software engineer and from my work experience and knowledge, this is one of the best channel that digs into the ways of working and architecturing an enterprise software. Kudos 👏

  • @kakanishrikant
    @kakanishrikant 2 года назад +27

    This is by far the BEST VIDEO on questions like "Design Yelp". Pure Gold !! Thanks, Alex, and ByteByteGo team for your outstanding work.

  • @bkswain101
    @bkswain101 2 года назад +10

    I have been following a number of channels related to system design in last few months. While many of them are brilliant, Sahn has a very unique and effective way of communicating complex technical topics. Thanks Sahn and team for this content. Hope to see more of these.

  • @pixusru
    @pixusru 8 месяцев назад +1

    I got this question on my Meta on-site interview. Absolutely bombed it.

  • @M3t4lstorm
    @M3t4lstorm 2 года назад +15

    Notes:
    - The SQL query at 20:27 would not work for the same reasons you mentioned previously in the video (prime meridian + equator).
    - You assume that the long/lat is the centre of the business/place, if users are able to add their own businesses this will probably not be the case
    - Businesses/places can span multiple grids (think of shopping malls)
    - Businesses/places can be bigger than a grid (think of airports)
    - At the very end you say it would "use the long/lat to rank the businesses and return to the client" (sorting), you also need to check if the business is still within the radius the user specified (filter); just because the business is in the same grid/neighbouring grids doesn't mean its within the radius they asked for.
    The first thought might be to make the geohash a list (of all the grids that it covers), but how do you calculate that? You would need a polygon (a long/lats for each vertex) that covers the (rough?) area of the business/place, then you get onto the trouble of validating that :)

  • @robl39
    @robl39 Год назад +2

    This is hands down the best design video I’ve ever seen

  • @arpanghoshal2579
    @arpanghoshal2579 2 года назад +5

    By far the best system design channel ever. Crisp presentation and fluid animations to easily showcase complex topics in a simple manner.

  • @alfazahmed
    @alfazahmed Год назад

    This has to be the highest quality system design explainer video on RUclips. * take a bow *

  • @深夜-l9f
    @深夜-l9f Год назад

    he explains like a teacher you would find in a school that everyone loves

  • @MaxRunia
    @MaxRunia 2 года назад +5

    I bought Vol 2 but I find video format slightly easier to digest. I really appreciate you making these videos.

  • @andreishakh4863
    @andreishakh4863 2 года назад +1

    I had exactly this problem on my system design interview @ faang, failed it miserably)) Excellent quality of material here, will help a lot in future!

  • @ksuhdilla
    @ksuhdilla 2 года назад +1

    This is such an underrated channel - very good visuals, concise speech pattern, and extremely well thought out approach to each topic

  • @TheMeanmachine1989
    @TheMeanmachine1989 2 года назад +3

    Thank you so much for starting to make these videos. Your step by step approach is so clear and crisp. Best System Design material ever!!!

  • @josephlabs
    @josephlabs 2 года назад

    Literally was designing a location based service and wanted advice, its criminal that you don't have more subs and views.

  • @mattbutalla6498
    @mattbutalla6498 Год назад +1

    I worked on a weather alert system that used S2, you more or less described its design and all the rationale for our decisions (we indexed by S2 cell id). Excellent video.

    • @mattbutalla6498
      @mattbutalla6498 Год назад

      And for the record, because of this I bought your vol 2 of sys design

  • @huynguyenquang2656
    @huynguyenquang2656 Год назад

    i hope u make 10 videos everyday so i can learn forever about system design. Thanks so much

  • @gauravgarg2344
    @gauravgarg2344 2 года назад +2

    As humble as he is, his videos are super awesome too. Go alex..!!

  • @dominusgloriae
    @dominusgloriae 2 года назад

    I'm really lucky to see this video released. It's been about a year since I work in the area of location based service. There is not much of related information that is up to date.
    Thanks a lot for this video! Keep on!

    • @ChrisCox-wv7oo
      @ChrisCox-wv7oo 2 года назад

      Are you saying the video information is out of date, or up to date?

    • @dominusgloriae
      @dominusgloriae 2 года назад +1

      @@ChrisCox-wv7oo it's up to date

  • @arekf3470
    @arekf3470 2 года назад +1

    Please continue making videos. The speaker did an amazing job, clear with a nice tone. The visual presentation is also nicely executed. 10/10, subscribed.

  • @nathanthainguyen
    @nathanthainguyen 2 года назад

    This channel gonna blowup. The graphic designs are the game changer

  • @aaditkamat4995
    @aaditkamat4995 2 года назад +1

    I am currently going through the System Design Course offered by Design Gurus on Educative which covers similar concepts but in a text based format. I have heard a lot about ByteByteGo's courses and books as well and I'm glad that I looked up this video. Thanks Alex and the team!

  • @effy1219
    @effy1219 2 года назад

    I've watched like most of the SD videos from YT, i could tell you guys this one is the best. Thanks Alex

  • @gigakoresh
    @gigakoresh 2 года назад +3

    Really good content, as always. You can also add a Kafka or some other streaming service to the business service, so that writes send events to the streaming system. You can then connect that streaming system to the write database as a sink, which will allow you to distribute the write loads evenly throughout the day and handle peak loads without consuming extra resources. Streaming systems like Kafka are so heavily optimized for such use-cases that even a relatively smol cluster with 3 4Gb+2CPU+100Gb should easily be able to handle these loads and have a lot of headroom if you use z-compression on the topic. As an added benefit you can perform change management on the database transparently to the user because streaming system will buffer all write operations automatically while the sink is offline. Streaming systems generally pair with a heavy read/low write system quite well.

    • @aniketshukla9568
      @aniketshukla9568 2 года назад

      Do we really need to add streaming services? I mean, as we know that write traffic is really very low and also we can compromise with the consistency(will be eventually consistent), so wouldn't Kafka or any streaming service be inefficient to use?

    • @gigakoresh
      @gigakoresh 2 года назад

      @@aniketshukla9568 Not with that kind of scale, no.

    • @hawkmne
      @hawkmne 3 месяца назад

      As he mentioned in the video, the number of write operations is very low hence no need for Kafka.

  • @king0s
    @king0s Год назад

    Beautiful poetry just opens up my eye. Overwhelmingly grateful. 🙏 and ❤from Chennai 🇮🇳

  • @RichardCurrie
    @RichardCurrie 2 года назад +1

    Currently the search API will need to query a few hundred businesses after the geoindex read. So business table will have 10x+ query load as the geoindex table

  • @red9090
    @red9090 2 года назад +3

    This was super fun to watch and got me interested again in algorithms and systems in general.
    I decided to go ahead and buy the two books straight ahead. So having a youtube channel definitely helps getting the word out :))

  • @stoneshou
    @stoneshou 2 года назад +9

    Hi Sam, you mention use (geohash, business id) as a compound key so we can remove business from the table efficiently. I don't think that's the right thing to do. Instead of a compound key, we should just add another index for the business id. Removing a business thus would only need to check that index. With a compound key we'd need to calculate the geohash for that business, walk the geohash index first, then look for the business id.

  • @kamal-xd7id
    @kamal-xd7id Год назад +4

    If we can have some sort of video course also like the book you published, I would buy the course right away. The content and the explanation you deliver is really simple to understand and that's the beauty of a good Teacher. "Explain me like I am 5th grade" This really goes for you!

  • @Fahadahammed
    @Fahadahammed Год назад

    Your approach is fascinating. It kept me watching the whole video and I find this very rare. Thank you.

  • @user-yr1uq1qe6y
    @user-yr1uq1qe6y 2 года назад +81

    In early 2000s we designed such a system for a popular real estate site very similar. We thought we had nailed the algorithm, but started getting complaints from agents and consumers.
    It turns out in that domain “distance” is almost always driving distance which is an entirely different problem and was much more complex in the days before quick road route planning 😀

    • @kumarsamaksha7207
      @kumarsamaksha7207 2 года назад +1

      Damn where do you work now?

    • @user-yr1uq1qe6y
      @user-yr1uq1qe6y 2 года назад +5

      @@kumarsamaksha7207 Nothing real estate related since 2008!

    • @kumarsamaksha7207
      @kumarsamaksha7207 2 года назад +1

      @@user-yr1uq1qe6y Cool

    • @ivanleon6164
      @ivanleon6164 2 года назад +2

      i think then you can increase the radius by a % and do a new query of driving distance on that reducer set and rearrange.

    • @riahmatic
      @riahmatic 2 года назад +3

      literally the traveling salesman problem :p

  • @sanathkumaru6358
    @sanathkumaru6358 2 года назад +2

    Please continue to make such wonderful videos. It’s pure gold, glad I discovered the channel.Thank you

  • @TheManTheMythThe
    @TheManTheMythThe 11 месяцев назад

    Would definitely love to get more full systems design interview videos like this from you. Great video!

  • @ЏонМастерман
    @ЏонМастерман Год назад

    You sir are a natural for teaching, please dont stop, you're doing world a favor! Cheers !

  • @nishantgarg2815
    @nishantgarg2815 2 года назад +17

    15:37 for 7-10, units would be in metre not km

  • @tommylongpham3889
    @tommylongpham3889 2 года назад +1

    I just started reading volume 2 of System Design Interview and I'm really enjoying the content so far. Even more so when I realized you created videos to further solidify the readings! Keep them coming!

  • @anup21d
    @anup21d Год назад

    A clear and in depth explanation of the proximity service design. Specifically I liked the detail ways to index the geospatial databse.

  • @deepakbhoria4172
    @deepakbhoria4172 Год назад

    I have tried different videos but this one definitely stands out for understanding location based system design.

  • @yonahkarp7273
    @yonahkarp7273 11 месяцев назад

    This is gold! Toss in a Geosptial DB on your interview and it’s sure to impress them

  • @mailsiraj
    @mailsiraj Год назад +1

    wow - what a wonderful video. So well thought out - clearly lays down the ideas using very easy to understand visuals.Thank you so much Alex.

  • @ovidiurosu6632
    @ovidiurosu6632 2 года назад

    This is the best system design video I've seen so far. Great job mister

  • @RahulSingh-ln7bg
    @RahulSingh-ln7bg 2 года назад +1

    Hi Alex, I think you need to correct the definition, at 14:00 onwards you are talking about quadtree, not Geohash, Geohash divides the grid initially into 32 smaller grids since the base here is 32. You may like to correct it.

  • @drucev
    @drucev 2 года назад +3

    excellent video ... I have one basic question, at 19:45, why do you use a compound key combining geohash and business id? if the business id is a unique key, then you are just concatenating some extra junk onto something which is already unique. or did I miss something, why does it make removal more efficient? good stuff!

  • @sergeykichuk2586
    @sergeykichuk2586 Год назад +2

    In this particular example Load balancer presented not well, because the idea 8:23 of load balancer is to distribute the same request to instances of the same service, here better would to say that there is API gateway and load balancer for each particular service instances!!

  • @amachefe0
    @amachefe0 2 года назад

    One of the best technical video i have ever watched

  • @joeb6705
    @joeb6705 Год назад

    This content is unbelievable. Will be checking out your books and newsletters!

  • @raymondmichael4987
    @raymondmichael4987 2 года назад

    I really like this video, the presenter is very friendly and calm, please extends this, I would like to learn more.
    You got +1 sub from Tanzania 🇹🇿
    Greetings from Tanzania 🇹🇿

  • @tqh28
    @tqh28 2 года назад

    you opened my mind about the system design. unbelievable

  • @tomeralmog424
    @tomeralmog424 Год назад +2

    Great video!
    Question please:
    Usually these services will have filters like business type, pricing etc.
    Which table would you add it to?

  • @eilselwerdna
    @eilselwerdna 2 года назад +1

    Amazing video thanks. One thing I did not quite get, are we storing the geohash of each location at the lowest (smallest) precision and letting the client work it out?

    • @ByteByteGo
      @ByteByteGo  2 года назад +3

      Right. We chose 3 precisions in our design, IIRC? The idea is to store at the smallest grid size of the three precisions, and the server could ask the database for the bigger grid sizes by constructing a query using the LIKE operator.

  • @andreffrosa
    @andreffrosa 2 года назад +1

    7:00 Why is it better to separate the two services than having just one web server doing both? The "you can scale them independently" doesn't suffice since you can scale the "merged" server as well or is there some hindrance on performance that I'm not seeing?

    • @GughaGSrinivasan
      @GughaGSrinivasan 2 года назад +1

      Location based Services could be used x10 times more than Business service... If you bundle it together like a monolithic model, in most of the cases Business service would be underutilized and wasting system resources... And for that reason, we can just segregate services based on usages/consumption... like in our example we separate Location Based Service instance and increase replica with 20 or more.... While Business service we can set the replicas with 4...

    • @andreffrosa
      @andreffrosa 2 года назад

      @@GughaGSrinivasan Thank you for your reply but it'l doesn't really answer the question. How exactly would it be underutilized and wasting resources if it is just a function that is invoked based on the type of request?

    • @GughaGSrinivasan
      @GughaGSrinivasan 2 года назад +1

      @@andreffrosa well you are not wrong with that solution... lets consider 1000 user wants to consume service A and 20 users for service B... service A response time is 1 sec... service B response time is 2 sec...
      If we bundle both these services together and scale this app, lets say 10 instances... lots of http thread requests for service A would block service B to effectively serve... and vice versa...
      If we segregate these services, we can scale 8 for Service A and 2 for service B... now both the service are functioning at best compared to previous solution...

    • @andreffrosa
      @andreffrosa 2 года назад

      ​@@GughaGSrinivasan "If we bundle both these services together and scale this app, lets say 10 instances... lots of http thread requests for service A would block service B to effectively serve... and vice versa..." how exactly would it block if requests are handled concurrently? You would only slowdown when all the servers are really congested but in that case you should really add another server anyway regardless of the option picked. Having 10 or 8+2 would still be 10 servers in total and each requests would take 1s and 2s anyway. What am I missing?

    • @andreffrosa
      @andreffrosa 2 года назад

      @@GughaGSrinivasan Assuming each request is from independent users that establish a different connection for each request.
      ​Case I:
      10 servers handling all requests
      80% 1s
      20% 2s
      max of 10K connections simultaneously per server
      (1) That would give an average of 0.8*10K connections with 1s and 0.2*10K connections with 2s, simultaneously per server.
      (2) Following that, we get an average of 0.9*10K connections handled per second per server ((0.8/1 + 0.2/2)*10K)
      (3) From there, the total number of requests processed per second by the whole system would be 10*0.9*10K = 90K on average.
      Case II:
      8 servers handling requests A (1s)
      2 servers handling requests B (2s)
      max of 10K connections simultaneously per server for both types of servers
      (1) That would give an average of 10K connections handled per second per server of type A and 5K connections handled per second per server of type B.
      (2) That entails a total of 8*10K requests processed per second of type A and 2*5K requests processed per second of type B (on average).
      (3) Overall, that would be 8*10K + 2*5K = 9*10K = 90K requests processed per second by the whole system on average.
      Did I make a mistake?

  • @kapilricky
    @kapilricky Год назад

    This is neat and effective. I only wish i saw this 3 years back when i was asked same in interview🙈😇

  • @ThugLifeModafocah
    @ThugLifeModafocah 2 года назад

    That geohash part was superb... Damn, so many things I didn't know.

  • @thephore
    @thephore 2 года назад +2

    This is one of the best technology videos I've ever watched! You explained everything very well and with great, informative graphics. Only small suggestion - maybe use a mono spaced font for the queries etc. to improve readability. Thanks for this!

  • @GughaGSrinivasan
    @GughaGSrinivasan 2 года назад +3

    I have your System Design Interview Volume I book... Never knew you were the author :) I learned CAP theorem, eventual consistency, and many others from it... I wasn't aware that there is volume 2.. will be adding it to my cart... Great explanation once again!

  • @bhagyashingale5663
    @bhagyashingale5663 2 года назад +2

    I would index the city column. This would prevent table scans. You can then further filter using geo data.

  • @ReflectionOcean
    @ReflectionOcean Год назад

    Functional vs non-functional
    Functional: start with the user personas and what they can do with the app. This determines the API design.
    Non-functional: think in terms of latency, throughput, storage. This determines the architecture, the data storage and retrieval implementations.

  • @doxologist
    @doxologist 2 года назад

    Amazing video. Only thing I'd add is timestamps on the video. But the content itself is priceless

  • @piero.guerrero
    @piero.guerrero 2 года назад +2

    Is a Load Balancer needed to balance the requests to the DB Read-only replicas?
    if not how the application decides where to read from? 🤔

  • @KGTube
    @KGTube 2 года назад

    The best System Design video so far! Thanks and Keep it going!

  • @SarKurd
    @SarKurd Год назад

    This video is so good, i need to watch it a few more times, there is a lot of valuable information here

  • @mahanteshambali
    @mahanteshambali 2 года назад +2

    As usual amazing video with great details. Thank you Alex. Wish to see more videos of length 20+ mins.

  • @essamgouda1609
    @essamgouda1609 2 года назад

    This is amazing, what a gem of a youtube channel !

  • @moranh461
    @moranh461 2 года назад +3

    Loved it, well made and highly educational. Looking forward for more of those.

  • @VladimirMinkin
    @VladimirMinkin 2 года назад +1

    How about using CouchDB for both cases (with sharding and clustering built-in)?

  • @pobodjjd
    @pobodjjd 10 месяцев назад

    Another great video with clear explanation and informative graphs for software engineers

  • @chrishabgood8900
    @chrishabgood8900 Год назад +1

    business info does not change very often so it would be a really good case for caching.

  • @amanrubey
    @amanrubey 2 года назад

    Absolutely love this video! 15 year old me craved this information but got it after 8 years

  • @NarayananPrabath
    @NarayananPrabath 2 года назад

    Alex. I am your great admirer. I would humbly request you to make more System design videos.

  • @thiagolopessilva
    @thiagolopessilva 2 года назад

    You are the best person to explain that content. Thanks to share it with us!

  • @petelin3181
    @petelin3181 2 года назад +4

    This is an awesome video. I liked how you were able to break down complex concepts so that even beginners could understood them at a high level. Was able to learn a lot under half an hour about the complete picture of system design

  • @thuantang
    @thuantang 2 года назад +1

    Absolutely love how succinct and on point the explanation is.

  • @user-jt5nd3yq4u
    @user-jt5nd3yq4u 10 месяцев назад

    This is by far the greatest video, thanks a lot for putting this together ❤

  • @cortfitzpatrick5700
    @cortfitzpatrick5700 5 месяцев назад

    Really great explanation. The thoughtful visuals helped me to understand much better.

  • @nayandas1774
    @nayandas1774 5 месяцев назад

    Thanks for this video! Cleared most of my problems in my upcoming project!! 😭😭

  • @ParisPolyzos
    @ParisPolyzos 2 года назад +4

    The design elements are at another level! Great work! Keep it up!

  • @DavidVillarama
    @DavidVillarama 2 года назад +2

    If you haven't work with geospatial indexing, how are you suppose to pass the interview? You'll probably be use up 20 minutes just trying to figure it out some on the fly solution with the one conducting the interview.

  • @bhavyemalhotra1584
    @bhavyemalhotra1584 3 месяца назад

    better than anything that I have found for this topic! Thanks!

  • @aba44614
    @aba44614 2 года назад

    I am truly thankful for these videos, please keep making more !

  • @imranhussain8700
    @imranhussain8700 2 года назад +2

    2 minutes in the video and liked it already 👍. What an amazing way of explaining stuff, simple yet effective slides. Thanks man appreciate your efforts.

  • @rouensk
    @rouensk 2 года назад +3

    Nice video. One suggestion though: naming the second table "geospatial_index" is mistake - naming by "technology" instead of "domain". It could be called "business_location" or "business_geo". That way, it is clear to which business entity ("business") it belongs, and if/when second business entity comes along, there would be no ambiguous naming etc.

  • @cem_kaya
    @cem_kaya 2 года назад +1

    You can also use a space filling curve for fast queries for 2d to 1d mapping

  • @bhatibhawani
    @bhatibhawani 2 года назад

    Best design videos I have ever. Keep the good work.

  • @solomonxie5157
    @solomonxie5157 2 года назад

    Excellent video! The core algorithm is from 11:56

  • @matiasmoresi5040
    @matiasmoresi5040 2 года назад +1

    Mindblowing content and way of presenting it! Thank you so much! Keep it up!

  • @sarathfromsaudi
    @sarathfromsaudi 2 года назад +1

    Excellent content. I liked your structured way of thinking

  • @prateek8837
    @prateek8837 Год назад +1

    So if I understood properly, given a (lat, long) you get geohash (using the library), and once you've have the geohash you find the nearby locations using a single search. Right?

  • @M1ntAll
    @M1ntAll 2 года назад

    Bought your book on system design. Great experience, thanks!

  • @stevecanny1583
    @stevecanny1583 2 года назад

    Thanks so much for this Sahn! I really appreciate the greater depth of this one :)

  • @joross8
    @joross8 2 года назад +1

    Fantastic system design content. Really appreciate the clear explanation of logic used to estimate the system requirements and then determine the approach to the design.

  • @rumeysadogan7444
    @rumeysadogan7444 2 года назад +1

    Another eye-opening video. Thank you very much for these high quality, insightful videos. Great work!!👏