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  • Uses of persistent data structures in non-functional languages

    - by Ray Toal
    Languages that are purely functional or near-purely functional benefit from persistent data structures because they are immutable and fit well with the stateless style of functional programming. But from time to time we see libraries of persistent data structures for (state-based, OOP) languages like Java. A claim often heard in favor of persistent data structures is that because they are immutable, they are thread-safe. However, the reason that persistent data structures are thread-safe is that if one thread were to "add" an element to a persistent collection, the operation returns a new collection like the original but with the element added. Other threads therefore see the original collection. The two collections share a lot of internal state, of course -- that's why these persistent structures are efficient. But since different threads see different states of data, it would seem that persistent data structures are not in themselves sufficient to handle scenarios where one thread makes a change that is visible to other threads. For this, it seems we must use devices such as atoms, references, software transactional memory, or even classic locks and synchronization mechanisms. Why then, is the immutability of PDSs touted as something beneficial for "thread safety"? Are there any real examples where PDSs help in synchronization, or solving concurrency problems? Or are PDSs simply a way to provide a stateless interface to an object in support of a functional programming style?

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  • Long-term Freelance contract: should it have a salary-day or not?

    - by otto
    I don't like to speak about money. I just like to work. I still believe in a relationship between good work and good compensation. Hence I don't want ask my employer about my compensations, actually they are asking me. So I created a liberal contract with unspecified salary-day -- I did not want to lose my rights to my own projects and I did not pay any attention to the salary-day. Now the firm said that they would have paid me 1 month earlier if I had provided a tax -paper. I provided it before the next payment -day (unspecified). During the next month, the co-employer pretty much blocks my working -- does not allow me to access working repository and the co-employer goes to cruise when we should finalize a project so I cannot do anything. Now the project is not finalized, the co-employer has apparently provided some false statements to the boss about my doings (not getting anything for one month's work and 1 month when the co-employer pretty much wasted just my time) -- I was only allowed to debug the code of my co-employer and not to do anything. I feel that co-employer did not allow me to work by purpose so that they have an excuse not to pay any salary. The co-employer says that I cannot speak to the boss. The boss say that I need to speak directly to co-employer, not to him. I haven't said anything about the situation. I did not get things done because I was not allowed and now I am not even allowed to speak. Boss is the person who pays salaries. But both boss and co-employer have stages in the firm -- I think co-employer and boss are the same person pretty much, they created a theatre so that they get almost 2 month's work for free. Now I have multiple ideas how to avoid this kind of situations in the future: specify the salary day make sure you can speak directly to the manager and the boss, not through middle-hand other?

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  • We are moving an Access based corporate front-end into a Web-based App

    - by Max Vernon
    We have an enterprise application with a front end written in Microsoft Access 2003 that has evolved over the past 6 years. The back end data, and a fair amount of back-end logic is contained within several Microsoft SQL Server databases. This front end app consists of around 180 forms, and over 120,000 lines of code, and interacts with VB.Net DLLs that support various critical functions used by our sales force. The current system makes use of 3 monitors to display various information; the Access app uses COM+ to control Microsoft Outlook and Internet Explorer for various purposes. The Access front end sometimes occupies 2 screens, automatically resizing itself based on Windows API-reported screen dimensions. The app also uses a Google map to present data to our agents, and allows two-way interactivity with the map through COM+ connectivity to JavaScript contained in the Google map. At the urging of senior management, we are looking to completely rewrite this application using some web-based technology, such as ASP.Net or perhaps a LAMP stack (the thinking with the LAMP stack thing is "free" is pretty cheap). We want to move to a web-based app so we can eliminate the dependency on our physical location for hiring new sales force members. Currently, our main office is full to capacity, and we need to continue growing the company. Does anyone have any thoughts on what would be the best technology to use for a web-based app of this magnitude? Keeping in mind the app is dependent on back-end services on our existing infrastructure. The app handles financial data and personal customer data, among other things. [I've looked at Best practices for moving large MS Access application towards .Net? and read the answers, and most of the comments. Interesting reading, and has some valid points, but our C.O.O. and contracted Software Architect are pushing for a full web-based app, not a .Net Windows App]

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  • is GTK Installation (PHP for desktop) affect the web application?

    - by Harshal Mahajan
    I just going to install the GTK for creating a desktop application. But I want to know if we install the GTK then is it affect our web application server or php.ini or other features of web based application? I know there is no requirement of server for desktop but the GTK create the other php.ini . so is it affect my other applications? I downloaded the GTK Tool kit from here. So I am just little bit confusing that it should not affect my all running web applications. I think the php for desktop is a very interesting issue for all of us, so I just want to know the affection of desktop on web?

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  • Conflict resolution for two-way sync

    - by K.Steff
    How do you manage two-way synchronization between a 'main' database server and many 'secondary' servers, in particular conflict resolution, assuming a connection is not always available? For example, I have an mobile app that uses CoreData as the 'database' on the iOS and I'd like to allow users to edit the contents without Internet connection. In the same time, this information is available on a website the devices will connect to. What do I do if/when the data on the two DB servers is in conflict? (I refer to CoreData as a DB server, though I am aware it is something slightly different.) Are there any general strategies for dealing with this sort of issue? These are the options I can think of: 1. Always use the client-side data as higher-priority 2. Same for server-side 3. Try to resolve conflicts by marking each field's edit timestamp and taking the latest edit Though I'm certain the 3rd option will open room for some devastating data corruption. I'm aware that the CAP theorem concerns this, but I only want eventual consistency, so it doesn't rule it out completely, right? Related question: Best practice patterns for two-way data synchronization. The second answer to this question says it probably can't be done.

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  • What is Rainbow (not the CMS)

    - by Jeremy Thompson
    I was reading this excellent blog article regarding speeding up the badge page and in the last comment the author @waffles (a.k.a Sam Saffron) mentions these tools: dapper and a bunch of custom helpers like rainbow, sql builder etc Dapper and sql builder was easy to look up but rainbow keeps pointing me to a CMS, can someone please point me to the real source? Thanks. Obviously the architecture of these [SE] sites is uber cool and ultra fast so no comments on that thanks.

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  • How to find out what Hackathons are coming up near me? [closed]

    - by codeulike
    I just went to my first hackathon (London GreenHackathon) and I want to go to lots more. Specifically, hackathons that have a theme of helping people or making the world a better place in some way. I know about Random Hacks of Kindness and a couple of others but is there some central aggregator that will help me find out about hackathons? Also, if anyone else can suggest specific hackathon initiatives I should check out that would be handy too. I'm in London but obviously for other people reading this question other locations will be of interest.

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  • Any algorithm to dedicate a set of known resources to a set of known requirements (scheduling)

    - by Saeed Neamati
    I'm developing an application to help school principals in dedicating teachers to classes and courses over the hours of a week (scheduling). The scenario is roughly something like this: User enters the list of teachers and their free times into the system User enters the list of courses for this semester User enters the list of available classes into the system Well, up to here, there is no big deal. Just simple CRUD operations and nothing extraordinary. However, now what makes this system useful is that the application should automatically and based on an algorithm create the semester scheduling. I think you've got the main idea here. For example application should suggest that teacher A should go to class 1 for mathematics, and at the same time teacher B should go to class 2 for physics. This way all of the classes would be dedicated to lessons and teacher times won't overlap each other. Piece a cake for school principal. However, I can't find a good algorithm for this resource dedication. I mean it seems hard to me. Searching Google resulted in articles from different websites, but they are of no help and use to me. For example: http://en.wikipedia.org/wiki/Resource_allocation or http://en.wikipedia.org/wiki/Scheduling_(production_processes) Is there any algorithm out there, or any application or engine which can help me here? Does this requirements have a known name, like for example time scheduling engine? Any help would be appreciated.

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  • What is the situation about OpenGL under Ubuntu Unity and Gnome3?

    - by user827992
    In a GNU/linux distribution is usually installed Xorg as main graphical server, it operates with a client-server logic, a special windows is designate as desktop environment and this special windows can handle all the eyecandy stuff like decorations, icons and effects. The problem is that the latest UI heavily relies on hardware acceleration, Unity is an overlay on Compiz and the Gnome-shell also require an active driver for the GPU to work well: the problem is: on the same OS I can find multiple implementations of OpenGL who is handling my OpenGL buffer? how the OpenGL buffer is managed compared to the other windows? how can I be sure that my OpenGL implementation is glued to the hardware and is not related to the client-server logic of Xorg? For example I have tried the clutter library and I have only experienced problems under both Unity and GTK/Gnome, no problem under other OS.

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  • Problem inserting pre-ordered values to quadtree

    - by Lucas Corrêa Feijó
    There's this string containing B, W and G (standing for black, white and gray). It defines the pre-ordered path of the quadtree I want to build. I wrote this method for filling the QuadTree class I also wrote but it doesn't work, it inserts correctly until it reaches a point in the algorithm it needs to "return". I use math quadrants convention order for insertion, such as northeast, northwest, southwest and southeast. A quadtree has all it's leafs black or white and all the other nodes gray The node used in the tree is called Node4T and has a char as data and 4 references to other nodes like itself, called, respectively NE, NW, SW, SE. public void insert(char val) { if(root==null) { root = new Node4T(val); } else { insert(root, val); } } public void insert(Node4T n, char c) { if(n.data=='G') // possible to insert { if(n.NE==null) { n.NE = new Node4T(c); return; } else { insert(n.NE,c); } if(n.NW==null) { n.NW = new Node4T(c); return; } else { insert(n.NW,c); } if(n.SW==null) { n.SW = new Node4T(c); return; } else { insert(n.SW,c); } if(n.SE==null) { n.SE = new Node4T(c); return; } else { insert(n.SE,c); } } else // impossible to insert { } } The input "GWGGWBWBGBWBWGWBWBWGGWBWBWGWBWBGBWBWGWWWB" is given a char at a time to the insert method and then the print method is called, pre-ordered, and the result is "GWGGWBWBWBWGWBWBW". How do I make it import the string correctly? Ignore the string reading process, suppose the method is called and it has to do it's job.

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  • Large enterprise application - clients wish to use duplicate e-mails addresses?

    - by Alex Key
    I'd like to know people's opinions, reactions to clients and technical work arounds (if applicable), to the issue of an enterprise application where a client wishes to use duplicate e-mail addresses? To clarify, when I say duplicate e-mail addresses I mean within the same client system, having multiple users that have the same e-mail address. So not just using generic e-mail addresses but using the e-mail address of another user. e.g. Bob Jenkins: [email protected] James Jeffery: [email protected] Context To give this some further context, in the e-learning sector it is common that although all staff in an organisation must complete e-learning - they may not have their own e-mail address so they choose to use their managers e-mail address. Albeit against good practice in public sites... it's a requirement we've over and over again where an organisation is split between office based staff and perhaps e.g. staff in a warehouse. Where problem lies Mr Steak, good point, the problem lies in password resets and perhaps in situations where semi-personal information could be sent (not confidential enough to worry about the insecurities of email). Perhaps reminders for specific system actions, which would be confusing for the unintended party to see (if perhaps misreading the e-mail's intended recipient) Possible solutions System knowing the difference between a "for the attention of" and direct to the person e-mails, including this in the body text. Using alternative communication such as SMS Simply not having e-mails sent to people who are not the intended recipient. Providing an e-mail service ourselfs (not really viable for a corporate IT dept) Thoughts?

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  • When module calling gets ugly

    - by Pete
    Has this ever happened to you? You've got a suite of well designed, single-responsibility modules, covered by unit tests. In any higher-level function you code, you are (95% of the code) simply taking output from one module and passing it as input to the next. Then, you notice this higher-level function has turned into a 100+ line script with multiple responsibilities. Here is the problem. It is difficult (impossible) to test that script. At least, it seems so. Do you agree? In my current project, all of the bugs came from this script. Further detail: each script represents a unique solution, or algorithm, formed by using different modules in different ways. Question: how can you remedy this situation? Knee-jerk answer: break the script up into single-responsibility modules. Comment on knee-jerk answer: it already is! Best answer I can come up with so far: create higher-level connector objects which "wire" modules together in particular ways (take output from one module, feed it as input to another module). Thus if our script was: FooInput fooIn = new FooInput(1, 2); FooOutput fooOutput = fooModule(fooIn); Double runtimevalue = getsomething(fooOutput.whatever); BarInput barIn = new BarInput( runtimevalue, fooOutput.someOtherValue); BarOutput barOut = barModule(BarIn); It would become with a connector: FooBarConnectionAlgo fooBarConnector = new fooBarConnector(fooModule, barModule); FooInput fooIn = new FooInput(1, 2); BarOutput barOut = fooBarConnector(fooIn); So the advantage is, besides hiding some code and making things clearer, we can test FooBarConnectionAlgo. I'm sure this situation comes up a lot. What do you do?

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  • Web Services and code lists

    - by 0x0me
    Our team heavily discuss the issues how to handle code list in a web service definition. The design goal is to describe a provider API to query a system using various values. Some of them are catalogs resp. code lists. A catalog or code list is a set of key value pairs. There are different systems (at least 3) maintaining possibly different code lists. Each system should implement the provider API, whereas each system might have different code list for the same business entity eg. think of colors. One system know [(1,'red'),(2,'green')] and another one knows [(1,'lightgreen'),(2,'darkgreen'),(3,'red')] etc. The access to the different provider API implementations will be encapsulated by a query service, but there is already one candidate which might use at least one provider API directly. The current options to design the API discussed are: use an abstract code list in the interface definition: the web service interface defines a well known set of code list which are expected to be used for querying and returning data. Each API provider implementation has to mapped the request and response values from those abstract codelist to the system specific one. let the query component handle the code list: the encapsulating query service knows the code list set of each provider API implementation and takes care of mapping the input and output to the system specific code lists of the queried system. do not use code lists in the query definition at all: Just query code lists by a plain string and let the provider API implementation figure out the right value. This might lead to a loose of information and possibly many false positives, due to the fact that the input string could not be canonical mapped to a code list value (eg. green - lightgreen or green - darkgreen or both) What are your experiences resp. solutions to such a problem? Could you give any recommendation?

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  • What's the normal way machine-learning algorithms are integrated into normal programs?

    - by Benjamin Pollack
    I'm currently taking a machine learning course for fun, and the course heavily focuses on Matlab/Octave to write the code. One thing mentioned in the course is that, while Matlab/Octave are great for prototyping, they're very rarely used for production algorithms. Instead, those algorithms are typically rewritten in C++/Python/etc., using appropriate libraries, before reaching customers. Fair enough; I get that. But here's my question: is that done for cultural reasons, for technical reasons, or because there is really no language that provides Matlab/Octave-like fluidity, but in a compiled form that can be linked from C/C++/$MainstreamLanguage? The game industry uses Lua for game logic because it's easy to embed, and vastly superior for expressing things like AI. Likewise, there are Prolog variants for rules-heavy applications, Scheme variants for compilers, and so on. If there's a matrix equivalent language, what is it? If there isn't, why is this field different?

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  • Issues signing up for Windows Azure free trial and pay as you go service

    - by Robert Greiner
    I get the following error when trying to sign up for the Azure 90-day free trial: We can't authorize the payment method. Please make sure the information is correct, or use another payment method. If you continue to get this message, please contact your financial institution. I've tried three different cards, two credit and one debit. Those cards are issued from two different banks. I've also tried the cards on two separate accounts. Someone from my work also confirmed that he could not sign up for the free trial either. Has anyone else had this problem? I haven't really seen much help searching Google and the support staff doesn't seem interested in helping people sign up for free accounts.

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  • When is it better to offload work to the RDBMS rather than to do it in code?

    - by GeminiDomino
    Okay, I'll cop to it: I'm a better coder than I am at databases, and I'm wondering where thoughts on "best practices" lie on the subject of doing "simple" calculations in the SQL query vs. in the code, such as this MySQL example (I didn't write it, I just have to maintain it!) -- This returns the username, and the users age as of the last event. SELECT u.username as user, IF ((DAY(max(e.date)) - DAY(u.DOB)) &lt; 0 , TRUNCATE(((((YEAR(max(e.date))*12)+MONTH(max(e.date))) -((YEAR(u.DOB)*12)+MONTH(u.DOB)))-1)/12, 0), TRUNCATE((((YEAR(max(e.date))*12)+MONTH(max(e.date))) - ((YEAR(u.DOB)*12)+MONTH(u.DOB)))/12, 0)) AS age FROM users as u JOIN events as e ON u.id = e.uid ... Compared to doing the "heavy" lifting in code: Query: SELECT u.username, u.DOB as dob, e.event_date as edate FROM users as u JOIN events as e ON u.id = e.uid code: function ageAsOfDate($birth, $aod) { //expects dates in mysql Y-m-d format... list($by,$bm,$bd) = explode('-',$birth); list($ay,$am,$ad) = explode('-',$aod); //Insert Calculations here ... return $Dy; //Difference in years } echo "Hey! ". $row['user'] ." was ". ageAsOfDate($row['dob'], $row['edate']) . " when we last saw him."; I'm pretty sure in a simple case like this it wouldn't make much difference (other than the creeping feeling of horror when I have to make changes to queries like the first one), but I think it makes it clearer what I'm looking for. Thanks!

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  • How to keep your eyes on the prize?

    - by Ziv
    I'm about to go in a very intensive programming course (8AM-8PM every day of the week for three months), at the end of which I will be given a developer job-the job's quality and the project I will work on will depend on my performance in the course. Getting a good position in the company could be very beneficial and I would very much want that, does anyone have specific techniques or ways that he keeps himself concentrated on a goal for a long period of time?

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  • Algorithmic problem - quickly finding all #'s where value %x is some given value

    - by Steve B.
    Problem I'm trying to solve, apologies in advance for the length: Given a large number of stored records, each with a unique (String) field S. I'd like to be able to find through an indexed query all records where Hash(S) % N == K for any arbitrary N, K (e.g. given a million strings, find all strings where HashCode(s) % 17 = 5. Is there some way of memoizing this so that we can quickly answer any question of this form without doing the % on every value? The motivation for this is a system of N distributed nodes, where each record has to be assigned to at least one node. The nodes are numbered 0 - (K-1) , and each node has to load up all of the records that match it's number: If we have 3 nodes Node 0 loads all records where Hash % 3 ==0 Node 1 loads all records where Hash % 3 ==1 Node 2 loads all records where Hash % 3 ==2 adding a 4th node, obviously all the assignments have to be recomputed - Node 0 loads all records where Hash % 4 ==0 ... etc I'd like to easily find these records through an indexed query without having to compute the mod individually. The best I've been able to come up with so far: If we take the prime factors of N (p1 * p2 * ... ) if N % M == I then p % M == I % p for all of N's prime factors e.g. 10 nodes : N % 10 == 6 then N % 2 = 0 == 6 %2 N % 5 = 1 == 6 %5 so storing an array of the "%" of N for the first "reasonable" number of primes for my data set should be helpful. For example in the above example we store the hash and the primes HASH PRIMES (array of %2, %3, %5, %7, ... ]) 16 [0 1 1 2 .. ] so looking for N%10 == 6 is equivalent to looking for all values where array[1]==1 and array[2] == 1. However, this breaks at the first prime larger than the highest number I'm storing in the factor table. Is there a better way?

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  • Why is database developer pay so high? [closed]

    - by user433500
    Just wondering why someone would get 10k+ in some area in US for just writing queries and creating tables. While the average salary for someone who does scripting, object oriented programming, J2EE and database all together is only ~12K in new york city. Is there similar opportunities in cities like new york where only doing database gets one 10K+? What is the rational of companies paying such a high salary to consultants for just writing simple queries? I am sure college grad can do that with ease and will be quite satisfied with a 60k+ pay for a couple of year. Does location really matter so much?

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  • Why do Core Data sqlite table columns start with 'Z'?

    - by Dia
    I was looking at the sqlite table that Core Data generates and noticed that all table columns start with 'Z'. I realize this is an implementation detail, but I was curious as to why that's the case and if there was a design decision involved in this. Anyone happen to know or guess why? Here's a sample schema output of Core Data sqlite database: sqlite .schema CREATE TABLE ZPOST ( Z_PK INTEGER PRIMARY KEY, Z_ENT INTEGER, Z_OPT INTEGER, ZPOSTID INTEGER, ZUSER INTEGER, ZCREATEDAT TIMESTAMP, ZTEXT VARCHAR ); CREATE TABLE ZUSER ( Z_PK INTEGER PRIMARY KEY, Z_ENT INTEGER, Z_OPT INTEGER, ZUSERID INTEGER, ZAVATARIMAGEURLSTRING VARCHAR, ZUSERNAME VARCHAR ); CREATE TABLE Z_METADATA (Z_VERSION INTEGER PRIMARY KEY, Z_UUID VARCHAR(255), Z_PLIST BLOB); CREATE TABLE Z_PRIMARYKEY (Z_ENT INTEGER PRIMARY KEY, Z_NAME VARCHAR, Z_SUPER INTEGER, Z_MAX INTEGER);

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  • What is a "cross-functional team" actually?

    - by Idsa
    The general meaning of "cross-functional team" is a team which combines specialists in different fields that are required to reach the goal. But it looks like in Agile cross-functionality means not only combining different specialists, but making them mix. Henrik Kniberg defines cross-functional team this way: "Cross-functional just means that the team as a whole has all skills needed to build the product, and that each team member is willing to do more than just their own thing." But where is the line drawn? Is it normal to ask developers to become testers for an iteration if it is required?

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  • Constructor should generally not call methods

    - by Stefano Borini
    I described to a colleague why a constructor calling a method can be an antipattern. example (in my rusty C++) class C { public : C(int foo); void setFoo(int foo); private: int foo; } C::C(int foo) { setFoo(foo); } void C::setFoo(int foo) { this->foo = foo } I would like to motivate better this fact through your additional contribute. If you have examples, book references, blog pages, or names of principles, they would be very welcome. Edit: I'm talking in general, but we are coding in python.

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  • Modular Database Structures

    - by John D
    I have been examining the code base we use in work and I am worried about the size the packages have grown to. The actual code is modular, procedures have been broken down into small functional (and testable) parts. The issue I see is that we have 100 procedures in a single package - almost an entire domain model. I had thought of breaking these packages down - to create sub domains that are centered around the procedure relationships to other objects. Group a bunch of procedures that have 80% of their relationships to three tables etc. The end result would be a lot more packages, but the packages would be smaller and I feel the entire code base would be more readable - when procedures cross between two domain models it is less of a struggle to figure which package it belongs to. The problem I now have is what the actual benefit of all this would really be. I looked at the general advantages of modularity: 1. Re-usability 2. Asynchronous Development 3. Maintainability Yet when I consider our latest development, the procedures within the packages are already reusable. At this advanced stage we rarely require asynchronous development - and when it is required we simply ladder the stories across iterations. So I guess my question is if people know of reasons why you would break down classes rather than just the methods inside of classes? Right now I do believe there is an issue with these mega packages forming but the only benefit I can really pin down to break them down is readability - something that experience gained from working with them would solve.

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  • How should I practice web server administration?

    - by Astyanax
    Security students can practice their skills with software like OWASP's webgoat or something similar to "hackthissite". Students interested in Operating Systems can study MINIX and PintOS, write shell scripts or study POSIX system calls. What would be the best course of action in order to practice Server Administration? Is there any such software/resource available, teaching you such skills with small lessons, or it is totally up to you? I've practiced live FreeBSD server administration and management of VMs (CentOS, Gentoo, Debian) under VirtualBox, but I always feel that this isn't enough and I must push myself harder. So, what would you recommend? What has worked for you?

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  • When and why are certain data structures used in the context of web development?

    - by Ein Doofus
    While browsing around the MSDN I came across: http://msdn.microsoft.com/en-us/library/aa287104%28v=vs.71%29 which lists various data structures such as: Queues Stacks Hashtables Binary Trees Binary Search Trees Graphs (I believe there are also Lists) and I was hoping to get a high-level overview of when these various data structures can be used in the broad context of web development, and when used, why one data structure is generally used instead of any other one.

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