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• "Never to forget information" for programmers [closed]

  - by Milan

  Hi there! I'm new to programming and I would like to make a list of most important pieces of knowledge of programming and CS that would be useful no matter what specific programming language I would use in the future. For instance, if I would make this kind of list for Law studies, there would be stuff like Articles of Constitution etc. Those pieces of information I would put in Anki, and repeat it from time to time. Speaking in terms of CS and programming I mean on the most useful: mathematical theorems algorithms (examples of elegant solutions, comparison of two solutions etc.) pieces of code anything else that is vital (and very handy) to have in mind Do you think that making this kind of knowledge list makes sense?

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• Why are software schedules so hard to define?

  - by 0A0D

  It seems that, in my experience, getting us engineers to accurately estimate and determine tasks to be completed is like pulling teeth. Rather than just giving a swag estimate of 2-3 weeks or 3-6 months... what is the simplest way to define software schedules so they are not so painful to define? For instance, customer A wants a feature by 02/01/2011. How do you schedule time to implement this feature knowing that other bug fixes may be needed along the way and take up additional engineering time?

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• C: What is a good source to teach standard/basic code conventions to someone newly learning the language ?

  - by shan23

  I'm tutoring someone who can be described as a rank newcomer in C. Understandably, she does not know much about coding conventions generally practiced, and hence all her programs tend to use single letter vars, mismatched spacing/indentation and the like, making it very difficult to read/debug her endeavors. My question is, is there a link/set of guidelines and examples which she can use for adopting basic code conventions ? It should not be too arcane as to scare her off, yet inclusive enough to have the basics covered (so that no one woulc wince looking at the code). Any suggestions ?

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• Number of Classes in a Namespace - Code Smell?

  - by Tim Claason

  I have a C# library that's used by several executables. There's only a couple namespaces in the library, and I just noticed that one of the namespaces has quite a few classes in it. I've always avoided having too many classes in a single namespace because of categorization, and because subconsciously, I think it looks "prettier" to have a deeper hierarchy of namespaces. My question is: does anyone else consider it a "code smell" when a namespace has many classes - even if the classes relate to each other? Would you put in a lot of effort to find nuances in the classes that allows for subcategorization?

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• Data management in unexpected places

  - by Ashok_Ora

  Normal 0 false false false EN-US X-NONE X-NONE Data management in unexpected places When you think of network switches, routers, firewall appliances, etc., it may not be obvious that at the heart of these kinds of solutions is an engine that can manage huge amounts of data at very high throughput with low latencies and high availability. Consider a network router that is processing tens (or hundreds) of thousands of network packets per second. So what really happens inside a router? Packets are streaming in at the rate of tens of thousands per second. Each packet has multiple attributes, for example, a destination, associated SLAs etc. For each packet, the router has to determine the address of the next “hop” to the destination; it has to determine how to prioritize this packet. If it’s a high priority packet, then it has to be sent on its way before lower priority packets. As a consequence of prioritizing high priority packets, lower priority data packets may need to be temporarily stored (held back), but addressed fairly. If there are security or privacy requirements associated with the data packet, those have to be enforced. You probably need to keep track of statistics related to the packets processed (someone’s sure to ask). You have to do all this (and more) while preserving high availability i.e. if one of the processors in the router goes down, you have to have a way to continue processing without interruption (the customer won’t be happy with a “choppy” VoIP conversation, right?). And all this has to be achieved without ANY intervention from a human operator – the router is most likely to be in a remote location – it must JUST CONTINUE TO WORK CORRECTLY, even when bad things happen. How is this implemented? As soon as a packet arrives, it is interpreted by the receiving software. The software decodes the packet headers in order to determine the destination, kind of packet (e.g. voice vs. data), SLAs associated with the “owner” of the packet etc. It looks up the internal database of “rules” of how to process this packet and handles the packet accordingly. The software might choose to hold on to the packet safely for some period of time, if it’s a low priority packet. Ah – this sounds very much like a database problem. For each packet, you have to minimally · Look up the most efficient next “hop” towards the destination. The “most efficient” next hop can change, depending on latency, availability etc. · Look up the SLA and determine the priority of this packet (e.g. voice calls get priority over data ftp) · Look up security information associated with this data packet. It may be necessary to retrieve the context for this network packet since a network packet is a small “slice” of a session. The context for the “header” packet needs to be stored in the router, in order to make this work. · If the priority of the packet is low, then “store” the packet temporarily in the router until it is time to forward the packet to the next hop. · Update various statistics about the packet. In most cases, you have to do all this in the context of a single transaction. For example, you want to look up the forwarding address and perform the “send” in a single transaction so that the forwarding address doesn’t change while you’re sending the packet. So, how do you do all this? Berkeley DB is a proven, reliable, high performance, highly available embeddable database, designed for exactly these kinds of usage scenarios. Berkeley DB is a robust, reliable, proven solution that is currently being used in these scenarios. First and foremost, Berkeley DB (or BDB for short) is very very fast. It can process tens or hundreds of thousands of transactions per second. It can be used as a pure in-memory database, or as a disk-persistent database. BDB provides high availability – if one board in the router fails, the system can automatically failover to another board – no manual intervention required. BDB is self-administering – there’s no need for manual intervention in order to maintain a BDB application. No need to send a technician to a remote site in the middle of nowhere on a freezing winter day to perform maintenance operations. BDB is used in over 200 million deployments worldwide for the past two decades for mission-critical applications such as the one described here. You have a choice of spending valuable resources to implement similar functionality, or, you could simply embed BDB in your application and off you go! I know what I’d do – choose BDB, so I can focus on my business problem. What will you do? /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;}

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• "Imprinting" as a language feature?

  - by MKO

  Idea I had this idea for a language feature that I think would be useful, does anyone know of a language that implements something like this? The idea is that besides inheritance a class can also use something called "imprinting" (for lack of better term). A class can imprint one or several (non-abstract) classes. When a class imprints another class it gets all it's properties and all it's methods. It's like the class storing an instance of the imprinted class and redirecting it's methods/properties to it. A class that imprints another class therefore by definition also implements all it's interfaces and it's abstract class. So what's the point? Well, inheritance and polymorphism is hard to get right. Often composition gives far more flexibility. Multiple inheritance offers a slew of different problems without much benefits (IMO). I often write adapter classes (in C#) by implementing some interface and passing along the actual methods/properties to an encapsulated object. The downside to that approach is that if the interface changes the class breaks. You also you have to put in a lot of code that does nothing but pass things along to the encapsulated object. A classic example is that you have some class that implements IEnumerable or IList and contains an internal class it uses. With this technique things would be much easier Example (c#) [imprint List<Person> as peopleList] public class People : PersonBase { public void SomeMethod() { DoSomething(this.Count); //Count is from List } } //Now People can be treated as an List<Person> People people = new People(); foreach(Person person in people) { ... } peopleList is an alias/variablename (of your choice)used internally to alias the instance but can be skipped if not needed. One thing that's useful is to override an imprinted method, that could be achieved with the ordinary override syntax public override void Add(Person person) { DoSomething(); personList.Add(person); } note that the above is functional equivalent (and could be rewritten by the compiler) to: public class People : PersonBase , IList<Person> { private List<Person> personList = new List<Person>(); public override void Add(object obj) { this.personList.Add(obj) } public override int IndexOf(object obj) { return personList.IndexOf(obj) } //etc etc for each signature in the interface } only if IList changes your class will break. IList won't change but an interface that you, someone in your team, or a thirdparty has designed might just change. Also this saves you writing a whole lot of code for some interfaces/abstract classes. Caveats There's a couple of gotchas. First we, syntax must be added to call the imprinted classes's constructors from the imprinting class constructor. Also, what happends if a class imprints two classes which have the same method? In that case the compiler would detect it and force the class to define an override of that method (where you could chose if you wanted to call either imprinted class or both) So what do you think, would it be useful, any caveats? It seems it would be pretty straightforward to implement something like that in the C# language but I might be missing something :) Sidenote - Why is this different from multiple inheritance Ok, so some people have asked about this. Why is this different from multiple inheritance and why not multiple inheritance. In C# methods are either virtual or not. Say that we have ClassB who inherits from ClassA. ClassA has the methods MethodA and MethodB. ClassB overrides MethodA but not MethodB. Now say that MethodB has a call to MethodA. if MethodA is virtual it will call the implementation that ClassB has, if not it will use the base class, ClassA's MethodA and you'll end up wondering why your class doesn't work as it should. By the terminology sofar you might already confused. So what happens if ClassB inherits both from ClassA and another ClassC. I bet both programmers and compilers will be scratching their heads. The benefit of this approach IMO is that the imprinting classes are totally encapsulated and need not be designed with multiple inheritance in mind. You can basically imprint anything.

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• How To Easily Send Emails From The Windows Task Scheduler

  - by Chris Hoffman

  The Windows Task Scheduler can automatically send email at a specific time or in response to a specific event, but its integrated email feature won’t work very well for most users. Instead of using the Task Scheduler’s email feature to send emails, you can use the SendEmail utility. It allows you to construct a single-line command that authenticates with an SMTP server and sends an email. How To Create a Customized Windows 7 Installation Disc With Integrated Updates How to Get Pro Features in Windows Home Versions with Third Party Tools HTG Explains: Is ReadyBoost Worth Using?

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• concurrency::index<N> from amp.h

  - by Daniel Moth

  Overview C++ AMP introduces a new template class index<N>, where N can be any value greater than zero, that represents a unique point in N-dimensional space, e.g. if N=2 then an index<2> object represents a point in 2-dimensional space. This class is essentially a coordinate vector of N integers representing a position in space relative to the origin of that space. It is ordered from most-significant to least-significant (so, if the 2-dimensional space is rows and columns, the first component represents the rows). The underlying type is a signed 32-bit integer, and component values can be negative. The rank field returns N. Creating an index The default parameterless constructor returns an index with each dimension set to zero, e.g. index<3> idx; //represents point (0,0,0) An index can also be created from another index through the copy constructor or assignment, e.g. index<3> idx2(idx); //or index<3> idx2 = idx; To create an index representing something other than 0, you call its constructor as per the following 4-dimensional example: int temp[4] = {2,4,-2,0}; index<4> idx(temp); Note that there are convenience constructors (that don’t require an array argument) for creating index objects of rank 1, 2, and 3, since those are the most common dimensions used, e.g. index<1> idx(3); index<2> idx(3, 6); index<3> idx(3, 6, 12); Accessing the component values You can access each component using the familiar subscript operator, e.g. One-dimensional example: index<1> idx(4); int i = idx[0]; // i=4 Two-dimensional example: index<2> idx(4,5); int i = idx[0]; // i=4 int j = idx[1]; // j=5 Three-dimensional example: index<3> idx(4,5,6); int i = idx[0]; // i=4 int j = idx[1]; // j=5 int k = idx[2]; // k=6 Basic operations Once you have your multi-dimensional point represented in the index, you can now treat it as a single entity, including performing common operations between it and an integer (through operator overloading): -- (pre- and post- decrement), ++ (pre- and post- increment), %=, *=, /=, +=, -=,%, *, /, +, -. There are also operator overloads for operations between index objects, i.e. ==, !=, +=, -=, +, –. Here is an example (where no assertions are broken): index<2> idx_a; index<2> idx_b(0, 0); index<2> idx_c(6, 9); _ASSERT(idx_a.rank == 2); _ASSERT(idx_a == idx_b); _ASSERT(idx_a != idx_c); idx_a += 5; idx_a[1] += 3; idx_a++; _ASSERT(idx_a != idx_b); _ASSERT(idx_a == idx_c); idx_b = idx_b + 10; idx_b -= index<2>(4, 1); _ASSERT(idx_a == idx_b); Usage You'll most commonly use index<N> objects to index into data types that we'll cover in future posts (namely array and array_view). Also when we look at the new parallel_for_each function we'll see that an index<N> object is the single parameter to the lambda, representing the (multi-dimensional) thread index… In the next post we'll go beyond being able to represent an N-dimensional point in space, and we'll see how to define the N-dimensional space itself through the extent<N> class. Comments about this post by Daniel Moth welcome at the original blog.

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• Flash player (in Firefox) is unstable in 14.04

  - by henry

  For 13.10, I used this guide to get Intel iGPU-supported playback of flash videos in Firefox: http://www.webupd8.org/2013/09/adobe-flash-player-hardware.html All in all, Intel graphics acceleration for flash content was working just fine in 13.10, at least on my machine (with Xubuntu). I basically followed the guide to do the same for 14.04, but about 2-3 weeks ago flash videos started acting up. Whenever I have one instance of flash paused or stopped in one tab and go to the next tab to continue some song on Soundcloud or something, it's game over. I'm clueless as to what I can do here. Did anything change in the meantime?

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• How do I share different files in a git repo with different people?

  - by David Faux

  In a single directory with a Git root folder, I have a bunch of files. I am working on one of those files, X.py, with my friend Alice. The other files I am working on with other people. I want Alice (and everyone else) to have access to X.py. I want Alice to only have access to X.py though. How can I achieve this with Git? Is there a way I can split a directory into two repos? That sounds rather cumbersome. Maybe I could add a remote repo that Alice can access containing X.py?

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• Habanero

  - by csharp-source.net

  An Enterprise Application Framework for .Net that is ideally suited for developing applications in an agile manner. The framework is used for producing an application from the data layer through to the front-end. Free open source under the LGPL license, it includes ORM, code generation and runtime UI generation to create one application for the desktop & web. Features: * ORM: Map database tables to objects in code * Persist property values to and from the database * Define all mapping in a single XML file * Switch between database vendors with one setting * Support for MySQL, MS Sql Server, MS Access, Oracle, PostgreSQL, SQLite, Firebird * FireStarter GUI class definitions xml manager * Generate user interfaces and map properties to controls * Develop for both desktop (with Windows Forms) and web (with Gizmox' Visual WebGUI) * Generate new projects and code files * Generate UI forms from templates * Reverse engineer class definitions from existing databases * Support variable data sources, including an in-memory database. Ships with Firestarter a free database reverse engineering, Domain Modelling and Code Generator.

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• How do you handle increasingly long compile times when working with templates?

  - by Ghita

  I use Visual Studio 2012 and he have cases where we added templates parameters to a class "just" in order to introduce a "seam point" so that in unit-test we can replace those parts with mock objects. How do you usually introduce seam points in C++: using interfaces and/or mixing based on some criteria with implicit interfaces by using templates parameters also ? One reason to ask this is also because when compiling sometimes a single C++ file (that includes templates files, that could also include other templates) results in an object file being generated that takes in the order of around 5-10 seconds on a developer machine. VS compiler is also not particularly fast on compiling templates as far as I understand, and because of the templates inclusion model (you practically include the definition of the template in every file that uses it indirectly and possibly re-instantiate that template every time you modify something that has nothing to do with that template) you could have problems with compile times (when doing incremental compiling). What are your ways of handling incremental(and not only) compile time when working with templates (besides a better/faster compiler :-)).

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• Developing Schema Compare for Oracle (Part 5): Query Snapshots

  - by Simon Cooper

  If you've emailed us about a bug you've encountered with the EAP or beta versions of Schema Compare for Oracle, we probably asked you to send us a query snapshot of your databases. Here, I explain what a query snapshot is, and how it helps us fix your bug. Problem 1: Debugging users' bug reports When we started the Schema Compare project, we knew we were going to get problems with users' databases - configurations we hadn't considered, features that weren't installed, unicode issues, wierd dependencies... With SQL Compare, users are generally happy to send us a database backup that we can restore using a single RESTORE DATABASE command on our test servers and immediately reproduce the problem. Oracle, on the other hand, would be a lot more tricky. As Oracle generally has a 1-to-1 mapping between instances and databases, any databases users sent would have to be restored to their own instance. Furthermore, the number of steps required to get a properly working database, and the size of most oracle databases, made it infeasible to ask every customer who came across a bug during our beta program to send us their databases. We also knew that there would be lots of issues with data security that would make it hard to get backups. So we needed an easier way to be able to debug customers issues and sort out what strange schema data Oracle was returning. Problem 2: Test execution time Another issue we knew we would have to solve was the execution time of the tests we would produce for the Schema Compare engine. Our initial prototype showed that querying the data dictionary for schema information was going to be slow (at least 15 seconds per database), and this is generally proportional to the size of the database. If you're running thousands of tests on the same databases, each one registering separate schemas, not only would the tests would take hours and hours to run, but the test servers would be hammered senseless. The solution To solve these, we needed to be able to populate the schema of a database without actually connecting to it. Well, the IDataReader interface is the primary way we read data from an Oracle server. The data dictionary queries we use return their data in terms of simple strings and numbers, which we then process and reconstruct into an object model, and the results of these queries are identical for identical schemas. So, we can record the raw results of the queries once, and then replay these results to construct the same object model as many times as required without needing to actually connect to the original database. This is what query snapshots do. They are binary files containing the raw unprocessed data we get back from the oracle server for all the queries we run on the data dictionary to get schema information. The core of the query snapshot generation takes the results of the IDataReader we get from running queries on Oracle, and passes the row data to a BinaryWriter that writes it straight to a file. The query snapshot can then be replayed to create the same object model; when the results of a specific query is needed by the population code, we can simply read the binary data stored in the file on disk and present it through an IDataReader wrapper. This is far faster than querying the server over the network, and allows us to run tests in a reasonable time. They also allow us to easily debug a customers problem; using a simple snapshot generation program, users can generate a query snapshot that could be sent along with a bug report that we can immediately replay on our machines to let us debug the issue, rather than having to obtain database backups and restore databases to test systems. There are also far fewer problems with data security; query snapshots only contain schema information, which is generally less sensitive than table data. Query snapshots implementation However, actually implementing such a feature did have a couple of 'gotchas' to it. My second blog post detailed the development of the dependencies algorithm we use to ensure we get all the dependencies in the database, and that algorithm uses data from both databases to find all the needed objects - what database you're comparing to affects what objects get populated from both databases. We get information on these additional objects using an appropriate WHERE clause on all the population queries. So, in order to accurately replay the results of querying the live database, the query snapshot needs to be a snapshot of a comparison of two databases, not just populating a single database. Furthermore, although the code population queries (eg querying all_tab_cols to get column information) can simply be passed straight from the IDataReader to the BinaryWriter, we need to hook into and run the live dependencies algorithm while we're creating the snapshot to ensure we get the same WHERE clauses, and the same query results, as if we were populating straight from a live system. We also need to store the results of the dependencies queries themselves, as the resulting dependency graph is stored within the OracleDatabase object that is produced, and is later used to help order actions in synchronization scripts. This is significantly helped by the dependencies algorithm being a deterministic algorithm - given the same input, it will always return the same output. Therefore, when we're replaying a query snapshot, and processing dependency information, we simply have to return the results of the queries in the order we got them from the live database, rather than trying to calculate the contents of all_dependencies on the fly. Query snapshots are a significant feature in Schema Compare that really helps us to debug problems with the tool, as well as making our testers happier. Although not really user-visible, they are very useful to the development team to help us fix bugs in the product much faster than we otherwise would be able to.

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• Internal and external API architecture

  - by Tacomanator

  The company I work for maintains a successful SaaS product that grew "organically" over the years. We are planning to expand the line with a suite of new products that will share data with the existing product. To support this, we are looking to consolidate business logic into a single place: a web service layer. The WS layer will be used by: The web applications A tool to import data A tool to integrate with other client software (not an API per se) We also want to create an API that can be used by our customers that are capable of using it to create their own integrations. We are struggling with the following question: Should the internal API (aka the WS layer) and the external API be one in the same, with security and permission settings to control what can be done by who, or should they be two separate applications where the external API just calls the internal API like any other application? So far in our debate it seems that separating them may be more secure, but will add overhead. What have others done in a similar situation?

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• What is the name of this tree?

  - by Daniel

  It has a single root and each node has 0..N ordered sub-nodes . The keys represent a distinct set of paths. Two trees can only be merged if they share a common root. It needs to support, at minimum: insert, merge, enumerate paths. For this tree: The +-------+----------------+ | | | cat cow dog + +--------+ + | | | | drinks jumps moos barks + | milk the paths would be: The cat drinks milk The cow jumps The cow moos The dog barks It's a bit like a trie. What is it?

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• Computer Networks UNISA - Chap 8 &ndash; Wireless Networking

  - by MarkPearl

  After reading this section you should be able to Explain how nodes exchange wireless signals Identify potential obstacles to successful transmission and their repercussions, such as interference and reflection Understand WLAN architecture Specify the characteristics of popular WLAN transmission methods including 802.11 a/b/g/n Install and configure wireless access points and their clients Describe wireless MAN and WAN technologies, including 802.16 and satellite communications The Wireless Spectrum All wireless signals are carried through the air by electromagnetic waves. The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. The wireless spectrum falls between 9KHZ and 300 GHZ. Characteristics of Wireless Transmission Antennas Each type of wireless service requires an antenna specifically designed for that service. The service’s specification determine the antenna’s power output, frequency, and radiation pattern. A directional antenna issues wireless signals along a single direction. An omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions The geographical area that an antenna or wireless system can reach is known as its range Signal Propagation LOS (line of sight) uses the least amount of energy and results in the reception of the clearest possible signal. When there is an obstacle in the way, the signal may… pass through the object or be obsrobed by the object or may be subject to reflection, diffraction or scattering. Reflection – waves encounter an object and bounces off it. Diffraction – signal splits into secondary waves when it encounters an obstruction Scattering – is the diffusion or the reflection in multiple different directions of a signal Signal Degradation Fading occurs as a signal hits various objects. Because of fading, the strength of the signal that reaches the receiver is lower than the transmitted signal strength. The further a signal moves from its source, the weaker it gets (this is called attenuation) Signals are also affected by noise – the electromagnetic interference) Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. Frequency Ranges Older wireless devices used the 2.4 GHZ band to send and receive signals. This had 11 communication channels that are unlicensed. Newer wireless devices can also use the 5 GHZ band which has 24 unlicensed bands Narrowband, Broadband, and Spread Spectrum Signals Narrowband – a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies Broadband – uses a relatively wide band of the wireless spectrum and offers higher throughputs than narrowband technologies The use of multiple frequencies to transmit a signal is known as spread-spectrum technology. In other words a signal never stays continuously within one frequency range during its transmission. One specific implementation of spread spectrum is FHSS (frequency hoping spread spectrum). Another type is known as DSS (direct sequence spread spectrum) Fixed vs. Mobile Each type of wireless communication falls into one of two categories Fixed – the location of the transmitted and receiver do not move (results in energy saved because weaker signal strength is possible with directional antennas) Mobile – the location can change WLAN (Wireless LAN) Architecture There are two main types of arrangements Adhoc – data is sent directly between devices – good for small local devices Infrastructure mode – a wireless access point is placed centrally, that all devices connect with 802.11 WLANs The most popular wireless standards used on contemporary LANs are those developed by IEEE’s 802.11 committee. Over the years several distinct standards related to wireless networking have been released. Four of the best known standards are also referred to as Wi-Fi. They are…. 802.11b 802.11a 802.11g 802.11n These four standards share many characteristics. i.e. All 4 use half duplex signalling Follow the same access method Access Method 802.11 standards specify the use of CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to access a shared medium. Using CSMA/CA before a station begins to send data on an 802.11 network, it checks for existing wireless transmissions. If the source node detects no transmission activity on the network, it waits a brief period of time and then sends its transmission. If the source does detect activity, it waits a brief period of time before checking again. The destination node receives the transmission and, after verifying its accuracy, issues an acknowledgement (ACT) packet to the source. If the source receives the ACK it assumes the transmission was successful, – if it does not receive an ACK it assumes the transmission failed and sends it again. Association Two types of scanning… Active – station transmits a special frame, known as a prove, on all available channels within its frequency range. When an access point finds the probe frame, it issues a probe response. Passive – wireless station listens on all channels within its frequency range for a special signal, known as a beacon frame, issued from an access point – the beacon frame contains information necessary to connect to the point. Re-association occurs when a mobile user moves out of one access point’s range and into the range of another. Frames Read page 378 – 381 about frames and specific 802.11 protocols Bluetooth Networks Sony Ericson originally invented the Bluetooth technology in the early 1990s. In 1998 other manufacturers joined Ericsson in the Special Interest Group (SIG) whose aim was to refine and standardize the technology. Bluetooth was designed to be used on small networks composed of personal communications devices. It has become popular wireless technology for communicating among cellular telephones, phone headsets, etc. Wireless WANs and Internet Access Refer to pages 396 – 402 of the textbook for details.

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• Is it possible to remove a particular host key from known_hosts?

  - by Kaustubh P

  I usually end up deleting the entire known_hosts file, which I have no problems for. But just out of curiosity, Is it possible to remove just a single entry? I opened the known_hosts file, and other han understanding that the file contains fingerprints for a given machine, I ddnt understand anything. Below is the message I faced, which led me to ask this question. Add correct host key in /home/wissen16/.ssh/known_hosts to get rid of this message. Offending key in /home/wissen16/.ssh/known_hosts:1 RSA host key for foo.com has changed and you have requested strict checking. Host key verification failed. Thanks.

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• How do I get Picasa 3.9 to play .MOV files?

  - by user44405

  I have been using Picasa for years, first in XP then in Ubuntu from 8.04 onwards & now in Lubuntu 11.10. For 11.10, I downloaded Picasa3.9.0 from FileHippo & installed it in Wine. Everything works well, except it doesn't play videos from my camera - it just shows a thumbnail - whereas earlier versions played videos OK. The videos appear as **.MOV (QuickTime video) in file manager, & can be played by, for instance, GNOME MPlayer or Movie Player (but not properly by Banshee...). Is there some simple way of getting Picasa 3.9 to play them?

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• Why does Network-Manager close when it cannot bind to any connection?

  - by Agmenor

  When Network-Manager is not able to bind my Ubuntu to any connection, after a while it closes. The icon in the notification area (or indicator area) disappears, and it does not run any more. For instance this happens when there is really no ethernet network nor wireless one. Nonetheless this is a problem, since I often plug in my ethernet cable long after having booted my computer. As a hack I therefore hit Alt + F2, and type nm-applet. But I am not satisfied with this solution, because I think it is not intuitive enough. Is there a way to keep Network-Manager always running? I have Network-Manager 0.8.1 on Ubuntu 10.10, but this has been so for a long time, at least for one year.

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• Having a generic data type for a database table column, is it "good" practice?

  - by Yanick Rochon

  I'm working on a PHP project where some object (class member) may contain different data type. For example : class Property { private $_id; // (PK) private $_ref_id; // the object reference id (FK) private $_name; // the name of the property private $_type; // 'string', 'int', 'float(n,m)', 'datetime', etc. private $_data; // ... // ..snip.. public getters/setters } Now, I need to perform some persistence on these objects. Some properties may be a text data type, but nothing bigger than what a varchar may hold. Also, later on, I need to be able to perform searches and sorting. Is it a good practice to use a single database table for this (ie. is there a non negligible performance impact)? If it's "acceptable", then what could be the data type for the data column?

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• Any enlightenment for understanding Object Oriented Programming? [closed]

  - by ????

  I studied computer science near the end of 1980s, and wasn't taught OOP that formally. With Pascal or C, when I understand the top-down design of functions, and the idea of black box, then everything just seem to make sense, as if there is a "oh I get it!" -- some kind of totally getting it and enlightenment feeling. But with OOP, all I know was the mechanics: the class, instance, method, inheritance, polymorphism, encapsulation. It was like, I knew all the "this is how it is", but never had the feeling of "I totally get it", the enlightened feeling. Would somebody be able to describe it, or point to a chapter in some book or paper which talks about OOP so that the reader can feel: "I totally get it!" on OOP?

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• Finding it Hard to Deliver Right Customer Experience: Think BPM!

  - by Ajay Khanna

  Our relationship with our customers is not a just a single interaction and we should not treat it like one. A customer’s relationship with a vendor is like a journey which starts way before customer makes a purchase and lasts long after that. The journey may start with customer researching a product that may lead to the eventual purchase and may continue with support or service needs for the product. A typical customer journey can be represented as shown below: As you may notice, customers tend to use multiple channels to interact with a company throughout their journey.  They also expect that they should get consistent experience, no matter what interaction channel they may choose. Customers do not like to repeat the information they have already provided and expect companies to remember their preferences, and offer them relevant products and services. If the company fails to meet this expectation, customers not only will abandon the purchase and go to the competitor but may also influence others’ purchase decision. Gone are the days when word of mouth was the only medium, and the customer could influence “Six” others. This is the age of social media and customer’s good or bad experience, especially bad get highly amplified and may influence hundreds of others. Challenges that face B2C companies today include: Delivering consistent experience: The reason that delivering consistent experience is challenging is due to fragmented data, disjointed systems and siloed multichannel interactions. Customers tend to get different service quality if they use web vs. phone vs. store. They get different responses from different service agents or get inconsistent answers if they call sales vs. service group in the company. Such inconsistent experiences result in lower customer satisfaction or NPS (net promoter score) numbers. Increasing Revenue: To stay competitive companies frequently introduce new products and services. Delay in launching such offerings has a significant impact on revenue realization. In addition to new product revenue, there are multiple opportunities to up-sell and cross-sell that impact bottom line. If companies are not able to identify such opportunities, bring a product to market quickly, or not offer the right product to the right customer at the right time, significant loss of revenue may occur. Ensuring Compliance: Companies must be compliant to ever changing regulations, these could be about Know Your Customer (KYC), Export/Import regulations, or taxation policies. In addition to government agencies, companies also need to comply with the SLA that they have committed to their customers. Lapse in meeting any of these requirements may lead to serious fines, penalties and loss in business. Companies have to make sure that they are in compliance will all such regulations and SLA commitments, at any given time. With the advent of social networks and mobile technology, companies not only need to focus on process efficiency but also on customer engagement. Improving engagement means delivering the customer experience as the customer is expecting and interacting with the customer at right time using right channel. Customers expect to be able to contact you via any channel of their choice (web, email, chat, mobile, social media), purchase via any viable channel (web, phone, store, mobile). Customers expect companies to understand their particular needs and remember their preferences on repeated visits. To deliver such an integrated, consistent, and contextual experience, power of BPM in must. Your company may be organized in departments like Marketing, Sales, Service. You may hold prospect data in SFA, order information in ERP, customer issues in CRM. However, the experience delivered to the customer must not be constrained by your system legacy. BPM helps in designing the right experience for the right customer and integrates all the underlining channels, systems, applications to make sure right information will be delivered to the right knowledge worker or to the customer every single time.     Orchestrating information across all systems (MDM, CRM, ERP), departments (commerce, merchandising, marketing service) and channels (Email, phone, web, social)  is the key, and that’s what BPM delivers. In addition to orchestrating systems and channels for consistency, BPM also provides an ability for analysis and decision management. By using data from historical transactions, social media and from other systems, users can determine the customer preferences, customer value, and churn propensity. This information, in the context, is then used while making a decision at a process step. Working with real-time decision management system can also suggest right up-sell or cross-sell offers, discounts or next-best-action steps for a particular customer. Timely action on customer issues or request is also a key tenet of a good customer experience. BPM’s complex event processing capabilities help companies to take proactive actions before issues get escalated. BPM system can be designed to listen to a certain event patters then deduce from those customer situations (credit card stolen, baggage lost, change of address) and do a triage before situation goes out of control. If such a situation arises you can send alerts to right people or immediately invoke corrective actions. Last but not least one of BPM’s key values is to drive continuous improvement. Learning about customers past experiences, interactions and social conversations, provide valuable insight. Such insight can be used to improve products, customer facing processes, and customer experience. You may take these insights as an input to design better more efficient and customer friendly sales, contact center or self-service processes. If customer experience is important for your business, make sure you have incorporated BPM as a part of your strategy to design, orchestrate and improve your customer facing processes.

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• Cocos2d Tiled Dynamic Object Layer

  - by Rodrigo Camargo

  I'm trying to develop a cocos2d tiled based game using a sort of 'dynamic' object layer. What I want to do is after the tiled map is loaded, the user can drag something into the map and that will become an event when the 'hero' pass over it. I know how to build an object layer in tiled but it seems that is for fixed positions and what I want is a dynamic action position based on what the user can select. For instance, the user can drag a rock into a tile and when the character hit that rock he may die, or something. I'm a little lost about how to make it work. Do you have any idea of what should I use or what should I look for? Thanks in advance!

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• SDL2 with OpenGL -- weird results, what's wrong?

  - by ber4444

  I'm porting an app to iOS, and therefore need to upgrade it to SDL2 from SDL1.2 (so far I'm testing it as an on OS X desktop app only). However, when running the code with SDL2, I'm getting weird results as shown on the second image below (the first image is how it looks with SDL, correctly). The single changeset that causes this is this one, do you see something obviously wrong there, or does SDL2 have some OpenGL nuances I'm unaware of? My SDL is based on changeset dd7e57847ea9 from HG (since then there is one "Allow specifying of OpenGL 3.2 Core Profile on Mac OS X" commit, not sure if that would help).

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• Using dot To Access Object Attribute and Proper abstraction

  - by cobie

  I have been programming in python and java for quite a number of years and one thing i find myself doing is using the setters and getters from java in python but a number of blogs seem to think using the dot notation for access is the pythonic way. What I would like to know is if using dot to access methods does not violate abstraction principle. If for example I implement an attribute as a single object and use dot notation to access, if I wanted to change the code later so that the attribute is represented by a list of objects, that would require quite some heavy lifting which violates abstraction principle.

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