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• Java NIO (Netty): How does Encryption or GZIPping work in theory (with filters)

  - by Tom

  Hello Experts, i would be very thankfull if you can explain to me, how in theory the "Interceptor/Filter" Pattern in ByteStreams (over Sockets/Channels) work (in Asynchronous IO with netty) in regard to encryption or compression of data. Given I have a Filter that does GZIPPING. How is this internally implemented? Does the Filter "collect" so many bytes form the channel, that this is a usefull number of bytes that can then be en/decoded? What is in general the minimal "blocksize(data to encode/decode in a chunk)" of socket based gzipping? Does this "blocksize" have to be negotiated in advance between server and client? What happens if the client does not send enough data to "fill" the blocksize (due to a network conquestion) but does not close the connection. Does this mean the other side will simply wait until it gets enough bytes to decode or until a timeout occoures...How is the Filter pattern the applied? The compression filter will de/compress the blocksize of bytes and then store them again in the same buffer would (in the case of netty) i normally be using the ChannelHanlderContext to pass the de/encoded data to the next filter?... Any explanations/links/tutorials (for beginners;-) will be very much appreciated to help me understand how for example encryption/compressing are implemented in socket based communication with filters/interceptor pattern. thank you very much tom

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• Ray-box Intersection Theory

  - by Myx

  Hello: I wish to determine the intersection point between a ray and a box. The box is defined by its min 3D coordinate and max 3D coordinate and the ray is defined by its origin and the direction to which it points. Currently, I am forming a plane for each face of the box and I'm intersecting the ray with the plane. If the ray intersects the plane, then I check whether or not the intersection point is actually on the surface of the box. If so, I check whether it is the closest intersection for this ray and I return the closest intersection. The way I check whether the plane-intersection point is on the box surface itself is through a function bool PointOnBoxFace(R3Point point, R3Point corner1, R3Point corner2) { double min_x = min(corner1.X(), corner2.X()); double max_x = max(corner1.X(), corner2.X()); double min_y = min(corner1.Y(), corner2.Y()); double max_y = max(corner1.Y(), corner2.Y()); double min_z = min(corner1.Z(), corner2.Z()); double max_z = max(corner1.Z(), corner2.Z()); if(point.X() >= min_x && point.X() <= max_x && point.Y() >= min_y && point.Y() <= max_y && point.Z() >= min_z && point.Z() <= max_z) return true; return false; } where corner1 is one corner of the rectangle for that box face and corner2 is the opposite corner. My implementation works most of the time but sometimes it gives me the wrong intersection. I was wondering if the way I'm checking whether the intersection point is on the box is correct or if I should use some other algorithm. Thanks.

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• Database theory - relationship between two tables

  - by iansinke

  I have a database with two tables - let's call them Foo and Bar. Each foo may be related to any number of bars, and each bar may be related to any number of foos. I want to be able to retrieve, with one query, the foos that are associated with a certain bar, and the bars that are associated with a certain foo. My question is, what is the best way of recording these relationships? Should I have a separate table with records of each relationship (e.g. two columns, foo and bar)? Should the foo table have a column for a list of bars, and vice versa? Is there another option that I'm overlooking? I'm using SQL Server, if that makes a difference.

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• Traceroute Theory

  - by Hamza Yerlikaya

  I am toying with trace route, my application send a ICMP echo request with a ttl of 0 every time i receive a time exceeded message i increment the ttl by one and resent the package, but what happens is I have 2 routers on my network i can trace the route through these router but third hop always ends up being one of the open dns servers same ip every time no matter where i traceroute to. AFAIK this is the correct traceroute implementation, can anyone tell me what i am doing wrong?

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• Discrete mathematics problem - Probability theory and counting

  - by Mohammad

  Hello All, I'm taking a discrete mathematics course, and I encountered a question and I need your help. I don't know if this is the right place for that though :) It says: Each user on a computer system has a password, which is six to eight characters long, where each character is an uppercase letter or a digit. Each password must contain at least one digit. How many possible passwords are there? The book solves this by adding the probabilities of having six,seven and eight characters long password. However, when he solves for probability of six characters he does this P6 = 36^6 - 26^6 and does P7 = 36^7 - 26^7 and P8 = 36^8 - 26^8 and then add them all I understand the solution, but my question is why doesn't calculating, P6 = 10*36^5 and the same for P7 and P8, work? 10 for the digit and 36 for the alphanumeric? Also, if anyone could give me another solution, other than the one in the book. Thank you very much :)

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• Theory of Game Interface Design

  - by anon

  Anyone know of a good book on Game Interface Design (not game play mechanics; the actual UI). I'm particular interested in theories of cognition, and how game interfaces are designed to allow the enduser efficient communication with the game (whether it in FPS, RTS, or so on). In a modern game, the amount of information conveyed to the user, the amount of choices the user can make; and the support for the user to make said decisions is simply astounding (think UIs for Starcraft II / WoW). Any insights into this would be greatly appreciated.

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• How to put theory into practise

  - by Dave greg

  I like to read alot of IT books e.g programming / functional. But the problem is that after reading I cannot find reasons to put it into practise and I soon forget what I read. Any advise?

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• Permutations distinct under given symmetry (Mathematica 8 group theory)

  - by Yaroslav Bulatov

  Given a list of integers like {2,1,1,0} I'd like to list all permutations of that list that are not equivalent under given group. For instance, using symmetry of the square, the result would be {{2, 1, 1, 0}, {2, 1, 0, 1}}. Approach below (Mathematica 8) generates all permutations, then weeds out the equivalent ones. I can't use it because I can't afford to generate all permutations, is there a more efficient way? Update: actually, the bottleneck is in DeleteCases. The following list {2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 0, 0, 0} has about a million permutations and takes 0.1 seconds to compute. Apparently there are supposed to be 1292 orderings after removing symmetries, but my approach doesn't finish in 10 minutes removeEquivalent[{}] := {}; removeEquivalent[list_] := ( Sow[First[list]]; equivalents = Permute[First[list], #] & /@ GroupElements[group]; DeleteCases[list, Alternatives @@ equivalents] ); nonequivalentPermutations[list_] := ( reaped = Reap@FixedPoint[removeEquivalent, Permutations@list]; reaped[[2, 1]] ); group = DihedralGroup[4]; nonequivalentPermutations[{2, 1, 1, 0}]

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• Goldbach theory in C

  - by nofe

  I want to write some code which takes any positive, even number (greater than 2) and gives me the smallest pair of primes that sum up to this number. I need this program to handle any integer up to 9 digits long. My aim is to make something that looks like this: Please enter a positive even integer ( greater than 2 ) : 10 The first primes adding : 3+7=10. Please enter a positive even integer ( greater than 2 ) : 160 The first primes adding : 3+157=160. Please enter a positive even integer ( greater than 2 ) : 18456 The first primes adding : 5+18451=18456. I don't want to use any library besides stdio.h. I don't want to use arrays, strings, or anything besides for the most basic toolbox: scanf, printf, for, while, do-while, if, else if, break, continue, and the basic operators (<,, ==, =+, !=, %, *, /, etc...). Please no other functions especially is_prime. I know how to limit the input to my needs so that it loops until given a valid entry. So now I'm trying to figure out the algorithm. I thought of starting a while loop like something like this: #include <stdio.h> long first, second, sum, goldbach, min; long a,b,i,k; //indices int main (){ while (1){ printf("Please enter a positive integer :\n"); scanf("%ld",&goldbach); if ((goldbach>2)&&((goldbach%2)==0)) break; else printf("Wrong input, "); } while (sum!=goldbach){ for (a=3;a<goldbach;a=(a+2)) for (i=2;(goldbach-a)%i;i++) first = a; for (b=5;b<goldbach;b=(b+2)) for (k=2;(goldbach-b)%k;k++) sum = first + second; } }

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• SQL Query Theory Question...

  - by Keng

  I have a large historical transaction table (15-20 million rows MANY columns) and a table with one row one column. The table with one row contains a date (last processing date) which will be used to pull the data in the trasaction table ('process_date'). Question: Should I inner join the 'process_date' table to the transaction table or the transaction table to the 'process_date' table?

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• C: theory on how to extract files from an archived file

  - by donok

  In C I have created a program which can archive multiple files into an archive file via the command line. e.g. $echo 'file1/2' > file1/2.txt $./archive file1.txt file2.txt arhivedfile $cat archivedfile file1 file2 How do I create a process so that in my archivedfile I have: header file1 end header file2 end They are all stored in the archive file one after another after another. I know that perhaps a header file is needed(containing filename, size of filename, start and end of file) for extracting these files back out into their original form, but how would I go about doing this. I am stuck on where and how to start. Please could someone help me on some logic as to how to approach extracting files back out of an archived file.

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• Very basic database theory.

  - by John R

  I have a set of tables to show the relationship between organziations and supporters below. Although I have done some basic mySQL querries, I know very little about database 'design'. I plan to querry the database for: -a list of contributors to a specific organization... or, -a list of organizations that a specific suporter supports. The database tables for organiations and contributors may have other columns in the future and recieve a lesser amount of querries based on that information. A | X A | Y A | Z B | X B | Y C | X C | Z How should the tables be set up? I assume that there should be a third table, but there is still redundent information in the third table. Is there a better way of setting up the tables? +----+-------+ +-------------+----------+ +----+-------+ | id | org | | org | contr | | id | contr.| +----+-------+ +-------------+----------+ +----+-------+ | 1 | A | | 1 | 1 | | 1 | X | | 2 | B | | 1 | 2 | | 2 | Y | | 3 | C | | 1 | 3 | | 3 | Z | +----+-------+ | 2 | 1 | +----+-------+ | 2 | 2 | | 3 | 1 | | 3 | 3 | +-------------+----------+

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• Do game-theoretic considerations stand in the way of this market-based game-mechanic achieving its goals?

  - by BerndBrot

  Mechanic The mechanic is called "market manipulation" and is supposed to work like this: Players can enter the London Stock Exchange (LSE) LSE displays the stock prices of 8 to 10 companies and derivatives. This number is relatively small to ensure that players will collide in their efforts to manipulate the market in their favor. The prices are calculated based on real world prices of these companies and derivatives (in real time) any market manipulations that were conducted by the players any market corrections of the system Players can buy and sell shares with cash, a resource in the game, at current in-game market value Players can manipulate the market, i.e. let the price of a share either rise or fall, by some amount, over a certain period of time. Manipulating the market requires spending certain in-game resources and is therefore limited. The system continuously corrects market manipulations by letting the in-game prices converge towards their real world counterparts at a rate of 2% of the difference between the two per hour. Because of this market correction mechanism, pushing up prices (and screwing down prices) becomes increasingly difficult the higher (lower) the price already is. Goals Players are supposed to collide (and have incentives to collide) in their efforts to manipulate the market in their favor, especially when it comes to manipulation efforts by different groups. Prices should not resolve around any equilibrium points. The more variance the better. Band-wagoning should always involve risk (recognizing that prices start rising should not be a sure sign that they will keep rising so that everybody can make easy profits even when they don't manipulate the market themselves) Question Are there any game-theoretic considerations that prevent the mechanic from achieving these goals?

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• Cuppa Corner talk "A trip to First Normal Form" available - Domains, Functional Dependencies, Repeat

  - by tonyrogerson

  It's 15 minutes, I talk about Domains, Functional Dependencies, Repeating Groups, Relational Valued Attributes and of course First Normal Form. http://sqlcontent.sqlblogcasts.com/video/cctr20100507dbdesign1nf/cctr20100507dbdesign1nf.html For questions just ask on the http://sqlserverfaq.com chat control or Twitter using #sqlfaq tag. Slides are also availble here: http://sqlcontent.sqlblogcasts.com/video/cctr20100507dbdesign1nf/cc_tr20100507_dbdesign1nf.pptx...(read more)

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• Data validation best practices: how can I better construct user feedback?

  - by Cory Larson

  Data validation, whether it be domain object, form, or any other type of input validation, could theoretically be part of any development effort, no matter its size or complexity. I sometimes find myself writing informational or error messages that might seem harsh or demanding to unsuspecting users, and frankly I feel like there must be a better way to describe the validation problem to the user. I know that this topic is subjective and argumentative. I've migrated this question from StackOverflow where I originally asked it with little response. Basically, I'm looking for good resources on data validation and user feedback that results from it at a theoretical level. Topics and questions I'm interested in are: Content Should I be describing what the user did correctly or incorrectly, or simply what was expected? How much detail can the user read before they get annoyed? (e.g. Is "Username cannot exceed 20 characters." enough, or should it be described more fully, such as "The username cannot be empty, and must be at least 6 characters but cannot exceed 30 characters."?) Grammar How do I decide between phrases like "must not," "may not," or "cannot"? Delivery This can depend on the project, but how should the information be delivered to the user? Should it be obtrusive (e.g. JavaScript alerts) or friendly? Should they be displayed prominently? Immediately (i.e. without confirmation steps, etc.)? Logging Do you bother logging validation errors? Internationalization Some cultures prefer or better understand directness over subtlety and vice-versa (e.g. "Don't do that!" vs. "Please check what you've done."). How do I cater to the majority of users? I may edit this list as I think more about the topic, but I'm genuinely interested in proper user feedback techniques. I'm looking for things like research results, poll results, etc. I've developed and refined my own techniques over the years that users seem to be okay with, but I work in an environment where the users prefer to adapt to what you give them over speaking up about things they don't like. I'm interested in hearing your experiences in addition to any resources to which you may be able to point me.

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• New book in the style of Advanced Programming Language Design by R. A. Finkel [closed]

  - by mfellner

  I am currently researching visual programming language design for a university paper and came across Advanced Programming Language Design by Raphael A. Finkel from 1996. Other, older discussions in the same vein on Stackoverflow have mentioned Language Implementation Patterns by Terence Parr and Programming Language Pragmatics* by Michael L. Scott. I was wondering if there is even more (and especially up-to-date) literature on the general topic of programming language design. *) http://www.cs.rochester.edu/~scott/pragmatics/

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• Why some consider static analysis a testing and some do not?

  - by user970696

  Preparing myself also to ISTQB certification, I found they call static analysis actually as a static testing, while some engineering book distinct between static analysis and testing, which is the dynamic activity. I tent to think that static analysis is not a testing in the true sense as it does not test, it checks/verifies. But sure I would love to hear opinion of the true experts here. Thank you

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• What is Granularity?

  - by tonyrogerson

  Granularity defines “the lowest level of detail”; but what is meant by “the lowest level of detail”? Consider the Transactions table below: create table Transactions ( TransactionID int not null primary key clustered, TransactionDate date not null, ClientID int not null, StockID int not null, TransactionAmount decimal ( 28 , 2 ) not null, CommissionAmount decimal ( 28 , 5 ) not null ) A Client can Trade in one or many Stocks on any date – there is no uniqueness to ClientID, Stock and TransactionDate...(read more)

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• Data validation best practices: how can I better construct user feedback?

  - by Cory Larson

  Data validation, whether it be domain object, form, or any other type of input validation, could theoretically be part of any development effort, no matter its size or complexity. I sometimes find myself writing informational or error messages that might seem harsh or demanding to unsuspecting users, and frankly I feel like there must be a better way to describe the validation problem to the user. I know that this topic is subjective and argumentative. StackOverflow might not be the proper channel for diving into this subject, but like I've mentioned, we all run into this at some point or another. There are so many StackExchange sites now; if there is a better one, feel free to share! Basically, I'm looking for good resources on data validation and user feedback that results from it at a theoretical level. Topics and questions I'm interested in are: Content Should I be describing what the user did correctly or incorrectly, or simply what was expected? How much detail can the user read before they get annoyed? (e.g. Is "Username cannot exceed 20 characters." enough, or should it be described more fully, such as "The username cannot be empty, and must be at least 6 characters but cannot exceed 30 characters."?) Grammar How do I decide between phrases like "must not," "may not," or "cannot"? Delivery This can depend on the project, but how should the information be delivered to the user? Should it be obtrusive (e.g. JavaScript alerts) or friendly? Should they be displayed prominently? Immediately (i.e. without confirmation steps, etc.)? Logging Do you bother logging validation errors? Internationalization Some cultures prefer or better understand directness over subtlety and vice-versa (e.g. "Don't do that!" vs. "Please check what you've done."). How do I cater to the majority of users? I may edit this list as I think more about the topic, but I'm genuinely interest in proper user feedback techniques. I'm looking for things like research results, poll results, etc. I've developed and refined my own techniques over the years that users seem to be okay with, but I work in an environment where the users prefer to adapt to what you give them over speaking up about things they don't like. I'm interested in hearing your experiences in addition to any resources to which you may be able to point me.

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• Is finding graph minors without single node pinch points possible?

  - by Alturis

  Is it possible to robustly find all the graph minors within an arbitrary node graph where the pinch points are generally not single nodes? I have read some other posts on here about how to break up your graph into a Hamiltonian cycle and then from that find the graph minors but it seems to be such an algorithm would require that each "room" had "doorways" consisting of single nodes. To explain a bit more a visual aid is necessary. Lets say the nodes below are an example of the typical node graph. What I am looking for is a way to automatically find the different colored regions of the graph (or graph minors)

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• Theoretically bug-free programs

  - by user2443423

  I have read lot of articles which state that code can't be bug-free, and they are talking about these theorems: Halting problem Gödel's incompleteness theorem Rice's theorem Actually Rice's theorem looks like an implication of the halting problem and the halting problem is in close relationship with Gödel's incompleteness theorem. Does this imply that every program will have at least one unintended behavior? Or does it mean that it's not possible to write code to verify it? What about recursive checking? Let's assume that I have two programs. Both of them have bugs, but they don't share the same bug. What will happen if I run them concurrently? And of course most of discussions talked about Turing machines. What about linear-bounded automation (real computers)?

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• Is code that terminates on a random condition guaranteed to terminate?

  - by Simon Campbell

  If I had a code which terminated based on if a random number generator returned a result (as follows), would it be 100% certain that the code would terminate if it was allowed to run forever. while (random(MAX_NUMBER) != 0): // random returns a random number between 0 and MAX_NUMBER print('Hello World') I am also interested in any distinctions between purely random and the deterministic random that computers generally use. Assume the seed is not able to be known in the case of the deterministic random. Naively it could be suggested that the code will exit, after all every number has some possibility and all of time for that possibility to be exercised. On the other hand it could be argued that there is the random chance it may not ever meet the exit condition-- the generator could generate 1 'randomly' until infinity. (I suppose one would question the validity of the random number generator if it was a deterministic generator returning only 1's 'randomly' though)

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• Which would be a better way to load data via ajax

  - by Mike

  I am using google maps and returning html/lat/long from my MySQL database Currently A user picks a business category e.g; "Video Production". an ajax call is sent to a CodeIgniter controller the Controller then queries the db, and returns the following data via JSON Lat/Long of the marker HTML for the popup window this is approximately 34 rows in the database across two tables per business the ajax call receives this data and then plots the marker along with the html onto the map The data that is returned from the controller is one big json object... This is done for all businesses that exist in the Video Production category (currently approx 40 businesses). As you can see, pulling this data for multiple categories (100s of businesses) can get very very taxing on the server. My question is Would it be more beneficial to modify the process flow as such: a user picks a business category e.g; "Video Production". an ajax call is sent to a CodeIgniter controller the controller then queries the database for the location base information lat/long level (used to change marker icon color) This would be a single row per business with several columns the ajax call receives this data and then plots the marker on the map when the user clicks a marker an ajax call is sent to a CodeIgniter Controller the controller queries the database for the HTML and additional data based on business_id and if not, what are some better suggestions to this problem? In summary this means rather than including the HTML and additional data along for each business, only submitting minimal location information and then re-query for that information when each business marker is clicked. Potential Downsides longer load times when a user clicks a marker icon more code?? more queries to the database

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• Don Knuth and MMIXAL vs. Chuck Moore and Forth -- Algorithms and Ideal Machines -- was there cross-pollination / influence in their ideas / work?

  - by AKE

  Question: To what extent is it known (or believed) that Chuck Moore and Don Knuth had influence on each other's thoughts on ideal machines, or their work on algorithms? I'm interested in citations, interviews, articles, links, or any other sort of evidence. It could also be evidence of the form of A and B here suggest that Moore might have borrowed or influenced C and D from Knuth here, or vice versa. (Opinions are of course welcome, but references / links would be better!) Context: Until fairly recently, I have been primarily familiar with Knuth's work on algorithms and computing models, mostly through TAOCP but also through his interviews and other writings. However, the more I have been using Forth, the more I am struck by both the power of a stack-based machine model, and the way in which the spareness of the model makes fundamental algorithmic improvements more readily apparent. A lot of what Knuth has done in fundamental analysis of algorithms has, it seems to me, a very similar flavour, and I can easily imagine that in a parallel universe, Knuth might perhaps have chosen Forth as his computing model. That's the software / algorithms / programming side of things. When it comes to "ideal computing machines", Knuth in the 70s came up with the MIX computer model, and then, collaborating with designers of state-of-the-art RISC chips through the 90s, updated this with the modern MMIX model and its attendant assembly language MMIXAL. Meanwhile, Moore, having been using and refining Forth as a language, but using it on top of whatever processor happened to be in the computer he was programming, began to imagine a world in which the efficiency and value of stack-based programming were reflected in hardware. So he went on in the 80s to develop his own stack-based hardware chips, defining the term MISC (Minimal Instruction Set Computers) along the way, and ending up eventually with the first Forth chip, the MuP21. Both are brilliant men with keen insight into the art of programming and algorithms, and both work at the intersection between algorithms, programs, and bare metal hardware (i.e. hardware without the clutter of operating systems). Which leads me to the headlined question... Question:To what extent is it known (or believed) that Chuck Moore and Don Knuth had influence on each other's thoughts on ideal machines, or their work on algorithms?

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• How to recover from finite-state-machine breakdown?

  - by Earl Grey

  My question may seems very scientific but I think it's a common problem and seasoned developers and programmers hopefully will have some advice to avoid the problem I mention in title. Btw., what I describe bellow is a real problem I am trying to proactively solve in my iOS project, I want to avoid it at all cost. By finite state machine I mean this I have a UI with a few buttons, several session states relevant to that UI and what this UI represents, I have some data which values are partly displayed in the UI, I receive and handle some external triggers (represented by callbacks from sensors). I made state diagrams to better map the relevant scenarios that are desirable and alowable in that UI and application. As I slowly implement the code, the app starts to behave more and more like it should. However, I am not very confident that it is robust enough. My doubts come from watching my own thinking and implementation process as it goes. I was confident that I had everything covered, but it was enough to make a few brute tests in the UI and I quickly realized that there are still gaps in the behavior ..I patched them. However, as each component depends and behaves based on input from some other component, a certain input from user or some external source trigers a chain of events, state changes..etc. I have several components and each behave like this Trigger received on input - trigger and its sender analyzed - output something (a message, a state change) based on analysis The problem is, this is not completely selfcontained, and my components (a database item, a session state, some button's state)...COULD be changed, influenced, deleted, or otherwise modified, outside the scope of the event-chain or desirable scenario. (phone crashes, battery is empty phone turn of suddenly) This will introduce a nonvalid situation into the system, from which the system potentially COULD NOT BE ABLE to recover. I see this (althought people do not realize this is the problem) in many of my competitors apps that are on apple store, customers write things like this "I added three documents, and after going there and there, i cannot open them, even if a see them." or "I recorded videos everyday, but after recording a too log video, I cannot turn of captions on them.., and the button for captions doesn't work".. These are just shortened examples, customers often describe it in more detail..from the descriptions and behavior described in them, I assume that the particular app has a FSM breakdown. So the ultimate question is how can I avoid this, and how to protect the system from blocking itself? EDIT I am talking in the context of one viewcontroller's view on the phone, I mean one part of the application. I Understand the MVC pattern, I have separate modules for distinct functionality..everything I describe is relevant to one canvas on the UI.

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