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• Remote objects activation doubt

  - by webdreamer

  If two clients do Activation.GetObject, using the Singleton approach, and the same address, are they going to get the same instance of the class? Or will each client get a different instance?

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• Best practice for using Wcf service by silverlight?

  - by bonefisher

  How would you structure the code for calling a wcf service in silverlight application? Using only-once instanciated wcf service-proxy (aka singleton) and using it across the whole SL app? If so, how did you solve the unsubscribing controls from ws-call-completed event? or creating the wcf service-proxy for each ws-call? Where do you close the proxy then?

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• Using static variables in Android

  - by michael

  Hi, In android, are using static variables a recommended practice? E.g, implementing a Singleton pattern in Java, I usually do: private static A the_instance; public static A getInstance() { if (the_instance == null) { the_instance = new A(); } return the_instance; } Also, when does this get cleaned up by the Android JVM? Thank you.

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• Ruby Module Inclusion in Methods

  - by Federico Builes

  In class Foo I'd like to include method Bar under certain conditions: module Bar def some_method "orly" end end class Foo def initialize(some_condition) if !some_condition "bar" else class << self; include Bar; end end end end Is there any cleaner (and clearer) way to achieve the include in the method without having to do it inside the singleton class?

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• Why and what for: java enum

  - by Mat Banik

  Today I was browsing through some question on this site and I found mention of enum being used in singleton pattern and that there are some thread safety benefits to such solution. I never used enums and I have been programing in java for more than couple a years now. And apparently they changed a lot and now they even do full blown support of OOP within them selfs. Now why and what for should I used enum in day to day programing?

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• Java reflection framework and security

  - by Jijoy

  Hi , Assume I have a singleton class in an external lib to my application. But still I can create instances of that particular class using reflection. Like this Class clas = Class.forName(Private.class.getName()); for(Constructor c : clas.getDeclaredConstructors()){ c.setAccessible(true); Private p = (Private) c.newInstance(); System.out.println(p); } How can I restrict this ? . Thanks J

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• Javascript plugin creation methods

  - by Aneesh

  I want to create a plugin 'myPlugin' which simply add some text to a div. like: document.getElementById('testDiv').myPlugin("this is a text"); how can I achieve this through singleton method as well as prototype method ?

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• Instantiating and referencing models in MVC

  - by fig-gnuton

  In MVC, should each model be a globally accessible singleton accessible to any view/controller? Or should the models be singletons that are dependency injected into any component that requires them? Or should a new model instance be created for each component that needs one, in which case events would be used to propagate changes across model instances of the same class?

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• How to display complex object in debugger?

  - by 4thSpace

  I'd like to display the contents of the property myarray, from the following singleton: [Session sharedManager].myarray I've tried these: po [Session sharedManager]. myarray po [[Session sharedManager] myarray] but always get this error: A syntax error near end of expression. Any suggestions?

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• Using static variable in android

  - by michael

  Hi, In android, is it recommend to use static variable? E.g, implement a Singleton pattern in Java, I usually do: private static A the_instance; public static A getInstance() { if (the_instance == null) { the_instance = new A(); } return the_instance; } My question is when do that get free by android JVM? Thank you.

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• Python `if x is not None` or `if not x is None`?

  - by orokusaki

  I've always thought of the if not x is None version to be more clear, but Google's style guide implies (based on this excerpt) that they use if x is not None. Is there any minor performance difference (I'm assuming not), and is there any case where one really doesn't fit (making the other a clear winner for my convention)?* *I'm referring to any singleton, rather than just None. ...to compare singletons like None. Use is or is not.

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• Does Application_Start block all incoming requests

  - by Jeeji

  Hi I have some code that initializes a static singleton class, which is needed by all requests. Therefore I thought I could add it to global.asax Application_Start. Can I be 100% sure that all requests will block while Application_Start is loading to guarantee that all the requests will have access to it? Thanks a lot Jeeji

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• Mocking with java 1.4

  - by Filip

  Is there any framework, whick allows to mock concrete classes, not only interfaces in java 1.4? I have third party code with a singleton class, where I wanna change one function, without touching orignal code. Is it possible?

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• AS3: How to dispatch from the document class?

  - by redconservatory

  I have a pretty good handle on dispatching from classes other than the Document Class, but what happens when I want to dispatch an event from the Document class and have other classes listen to the document class broadcast? It seems like there are several ways to approach this (i.e using a Singleton, using composition, using MovieClip(root)) I was just wondering what people find is the "best practice" way to do this?

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• Unittest in Django. Static variable feeded into the test case

  - by ziang

  I want to generate some dynamic data and feed these data in to test cases. But I found that Django will initial the test class every time to do the test. So the data will get generated every time django test framework calls the function. Is there anyway to use something like the singleton or static variable to solve the problem? What should be the solution? Thanks!

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• Php static variables across sessions

  - by pistacchio

  Hi, In ASP.NET if I declare a variable (or object) static (or if I make a singleton) I can have it persist across multiple sessions of multiple users (it it registered in a server scope) so that I don't have to initialize it at every request. Is there such a feature in PHP? Thanks

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• How to track how many times an iPhone app is opened?

  - by Jason

  I am building an iphone app and would like to keep track of how many times it has been opened so that I can prompt the user to do certain actions after it has been opened X number of times. I have thought about storing a variable in Core Data which I update every time it is opened, but this seems like a waste since it is a singleton data, not multiple instances of an object. What is the best way to store data like this and access it without slowing down the app opening time?

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• From Binary to Data Structures

  - by Cédric Menzi

  Table of Contents Introduction PE file format and COFF header COFF file header BaseCoffReader Byte4ByteCoffReader UnsafeCoffReader ManagedCoffReader Conclusion History This article is also available on CodeProject Introduction Sometimes, you want to parse well-formed binary data and bring it into your objects to do some dirty stuff with it. In the Windows world most data structures are stored in special binary format. Either we call a WinApi function or we want to read from special files like images, spool files, executables or may be the previously announced Outlook Personal Folders File. Most specifications for these files can be found on the MSDN Libarary: Open Specification In my example, we are going to get the COFF (Common Object File Format) file header from a PE (Portable Executable). The exact specification can be found here: PECOFF PE file format and COFF header Before we start we need to know how this file is formatted. The following figure shows an overview of the Microsoft PE executable format. Source: Microsoft Our goal is to get the PE header. As we can see, the image starts with a MS-DOS 2.0 header with is not important for us. From the documentation we can read "...After the MS DOS stub, at the file offset specified at offset 0x3c, is a 4-byte...". With this information we know our reader has to jump to location 0x3c and read the offset to the signature. The signature is always 4 bytes that ensures that the image is a PE file. The signature is: PE\0\0. To prove this we first seek to the offset 0x3c, read if the file consist the signature. So we need to declare some constants, because we do not want magic numbers.   private const int PeSignatureOffsetLocation = 0x3c; private const int PeSignatureSize = 4; private const string PeSignatureContent = "PE";   Then a method for moving the reader to the correct location to read the offset of signature. With this method we always move the underlining Stream of the BinaryReader to the start location of the PE signature.   private void SeekToPeSignature(BinaryReader br) { // seek to the offset for the PE signagure br.BaseStream.Seek(PeSignatureOffsetLocation, SeekOrigin.Begin); // read the offset int offsetToPeSig = br.ReadInt32(); // seek to the start of the PE signature br.BaseStream.Seek(offsetToPeSig, SeekOrigin.Begin); }   Now, we can check if it is a valid PE image by reading of the next 4 byte contains the content PE.   private bool IsValidPeSignature(BinaryReader br) { // read 4 bytes to get the PE signature byte[] peSigBytes = br.ReadBytes(PeSignatureSize); // convert it to a string and trim \0 at the end of the content string peContent = Encoding.Default.GetString(peSigBytes).TrimEnd('\0'); // check if PE is in the content return peContent.Equals(PeSignatureContent); }   With this basic functionality we have a good base reader class to try the different methods of parsing the COFF file header. COFF file header The COFF header has the following structure: Offset Size Field 0 2 Machine 2 2 NumberOfSections 4 4 TimeDateStamp 8 4 PointerToSymbolTable 12 4 NumberOfSymbols 16 2 SizeOfOptionalHeader 18 2 Characteristics If we translate this table to code, we get something like this:   [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)] public struct CoffHeader { public MachineType Machine; public ushort NumberOfSections; public uint TimeDateStamp; public uint PointerToSymbolTable; public uint NumberOfSymbols; public ushort SizeOfOptionalHeader; public Characteristic Characteristics; } BaseCoffReader All readers do the same thing, so we go to the patterns library in our head and see that Strategy pattern or Template method pattern is sticked out in the bookshelf. I have decided to take the template method pattern in this case, because the Parse() should handle the IO for all implementations and the concrete parsing should done in its derived classes.   public CoffHeader Parse() { using (var br = new BinaryReader(File.Open(_fileName, FileMode.Open, FileAccess.Read, FileShare.Read))) { SeekToPeSignature(br); if (!IsValidPeSignature(br)) { throw new BadImageFormatException(); } return ParseInternal(br); } } protected abstract CoffHeader ParseInternal(BinaryReader br);   First we open the BinaryReader, seek to the PE signature then we check if it contains a valid PE signature and rest is done by the derived implementations. Byte4ByteCoffReader The first solution is using the BinaryReader. It is the general way to get the data. We only need to know which order, which data-type and its size. If we read byte for byte we could comment out the first line in the CoffHeader structure, because we have control about the order of the member assignment.   protected override CoffHeader ParseInternal(BinaryReader br) { CoffHeader coff = new CoffHeader(); coff.Machine = (MachineType)br.ReadInt16(); coff.NumberOfSections = (ushort)br.ReadInt16(); coff.TimeDateStamp = br.ReadUInt32(); coff.PointerToSymbolTable = br.ReadUInt32(); coff.NumberOfSymbols = br.ReadUInt32(); coff.SizeOfOptionalHeader = (ushort)br.ReadInt16(); coff.Characteristics = (Characteristic)br.ReadInt16(); return coff; }   If the structure is as short as the COFF header here and the specification will never changed, there is probably no reason to change the strategy. But if a data-type will be changed, a new member will be added or ordering of member will be changed the maintenance costs of this method are very high. UnsafeCoffReader Another way to bring the data into this structure is using a "magically" unsafe trick. As above, we know the layout and order of the data structure. Now, we need the StructLayout attribute, because we have to ensure that the .NET Runtime allocates the structure in the same order as it is specified in the source code. We also need to enable "Allow unsafe code (/unsafe)" in the project's build properties. Then we need to add the following constructor to the CoffHeader structure.   [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)] public struct CoffHeader { public CoffHeader(byte[] data) { unsafe { fixed (byte* packet = &data[0]) { this = *(CoffHeader*)packet; } } } }   The "magic" trick is in the statement: this = *(CoffHeader*)packet;. What happens here? We have a fixed size of data somewhere in the memory and because a struct in C# is a value-type, the assignment operator = copies the whole data of the structure and not only the reference. To fill the structure with data, we need to pass the data as bytes into the CoffHeader structure. This can be achieved by reading the exact size of the structure from the PE file.   protected override CoffHeader ParseInternal(BinaryReader br) { return new CoffHeader(br.ReadBytes(Marshal.SizeOf(typeof(CoffHeader)))); }   This solution is the fastest way to parse the data and bring it into the structure, but it is unsafe and it could introduce some security and stability risks. ManagedCoffReader In this solution we are using the same approach of the structure assignment as above. But we need to replace the unsafe part in the constructor with the following managed part:   [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)] public struct CoffHeader { public CoffHeader(byte[] data) { IntPtr coffPtr = IntPtr.Zero; try { int size = Marshal.SizeOf(typeof(CoffHeader)); coffPtr = Marshal.AllocHGlobal(size); Marshal.Copy(data, 0, coffPtr, size); this = (CoffHeader)Marshal.PtrToStructure(coffPtr, typeof(CoffHeader)); } finally { Marshal.FreeHGlobal(coffPtr); } } }     Conclusion We saw that we can parse well-formed binary data to our data structures using different approaches. The first is probably the clearest way, because we know each member and its size and ordering and we have control about the reading the data for each member. But if add member or the structure is going change by some reason, we need to change the reader. The two other solutions use the approach of the structure assignment. In the unsafe implementation we need to compile the project with the /unsafe option. We increase the performance, but we get some security risks.

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• Unity: how to apply programmatical changes to the Terrain SplatPrototype?

  - by Shivan Dragon

  I have a script to which I add a Terrain object (I drag and drop the terrain in the public Terrain field). The Terrain is already setup in Unity to have 2 PaintTextures: 1 is a Square (set up with a tile size so that it forms a checkered pattern) and the 2nd one is a grass image: Also the Target Strength of the first PaintTexture is lowered so that the checkered pattern also reveals some of the grass underneath. Now I want, at run time, to change the Tile Size of the first PaintTexture, i.e. have more or less checkers depending on various run time conditions. I've looked through Unity's documentation and I've seen you have the Terrain.terrainData.SplatPrototype array which allows you to change this. Also there's a RefreshPrototypes() method on the terrainData object and a Flush() method on the Terrain object. So I made a script like this: public class AStarTerrain : MonoBehaviour { public int aStarCellColumns, aStarCellRows; public GameObject aStarCellHighlightPrefab; public GameObject aStarPathMarkerPrefab; public GameObject utilityRobotPrefab; public Terrain aStarTerrain; void Start () { //I've also tried NOT drag and dropping the Terrain on the public field //and instead just using the commented line below, but I get the same results //aStarTerrain = this.GetComponents<Terrain>()[0]; Debug.Log ("Got terrain "+aStarTerrain.name); SplatPrototype[] splatPrototypes = aStarTerrain.terrainData.splatPrototypes; Debug.Log("Terrain has "+splatPrototypes.Length+" splat prototypes"); SplatPrototype aStarCellSplat = splatPrototypes[0]; Debug.Log("Re-tyling splat prototype "+aStarCellSplat.texture.name); aStarCellSplat.tileSize = new Vector2(2000,2000); Debug.Log("Tyling is now "+aStarCellSplat.tileSize.x+"/"+aStarCellSplat.tileSize.y); aStarTerrain.terrainData.RefreshPrototypes(); aStarTerrain.Flush(); } //... Problem is, nothing gets changed, the checker map is not re-tiled. The console outputs correctly tell me that I've got the Terrain object with the right name, that it has the right number of splat prototypes and that I'm modifying the tileSize on the SplatPrototype object corresponding to the right texture. It also tells me the value has changed. But nothing gets updated in the actual graphical view. So please, what am I missing?

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• Building a StackOverflow inspired Knowledge Exchange Three Tiers to MVC – Hooray – Dependency Inject

  In this article we will address the lack of testability that our current application has. We will do this by making our application conform to the dependency injection pattern. This will allow us to push up all of our dependencies which makes our code considerably more testable than it currently is.

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• Building a StackOverflow inspired Knowledge Exchange Three Tiers to MVC – Hooray – Inversion of Cont

  In this article we will discuss how we can enhance the power of the Dependency Injection pattern by implementing an Inversion of Control container. We will discuss what an IoC container can be used for and how it works. Then we will look at implementing an Inversion of Control container in our code. We will specifically implement the IoC container StructureMap.

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• JavaScript Data Binding Frameworks

  - by dwahlin

  Data binding is where it’s at now days when it comes to building client-centric Web applications. Developers experienced with desktop frameworks like WPF or web frameworks like ASP.NET, Silverlight, or others are used to being able to take model objects containing data and bind them to UI controls quickly and easily. When moving to client-side Web development the data binding story hasn’t been great since neither HTML nor JavaScript natively support data binding. This means that you have to write code to place data in a control and write code to extract it. Although it’s certainly feasible to do it from scratch (many of us have done it this way for years), it’s definitely tedious and not exactly the best solution when it comes to maintenance and re-use. Over the last few years several different script libraries have been released to simply the process of binding data to HTML controls. In fact, the subject of data binding is becoming so popular that it seems like a new script library is being released nearly every week. Many of the libraries provide MVC/MVVM pattern support in client-side JavaScript apps and some even integrate directly with server frameworks like Node.js. Here’s a quick list of a few of the available libraries that support data binding (if you like any others please add a comment and I’ll try to keep the list updated): AngularJS MVC framework for data binding (although closely follows the MVVM pattern). Backbone.js MVC framework with support for models, key/value binding, custom events, and more. Derby Provides a real-time environment that runs in the browser an in Node.js. The library supports data binding and templates. Ember Provides support for templates that automatically update as data changes. JsViews Data binding framework that provides “interactive data-driven views built on top of JsRender templates”. jQXB Expression Binder Lightweight jQuery plugin that supports bi-directional data binding support. KnockoutJS MVVM framework with robust support for data binding. For an excellent look at using KnockoutJS check out John Papa’s course on Pluralsight. Meteor End to end framework that uses Node.js on the server and provides support for data binding on  the client. Simpli5 JavaScript framework that provides support for two-way data binding. WinRT with HTML5/JavaScript If you’re building Windows 8 applications using HTML5 and JavaScript there’s built-in support for data binding in the WinJS library.   I won’t have time to write about each of these frameworks, but in the next post I’m going to talk about my (current) favorite when it comes to client-side JavaScript data binding libraries which is AngularJS. AngularJS provides an extremely clean way – in my opinion - to extend HTML syntax to support data binding while keeping model objects (the objects that hold the data) free from custom framework method calls or other weirdness. While I’m writing up the next post, feel free to visit the AngularJS developer guide if you’d like additional details about the API and want to get started using it.

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• URL Routing in ASP.NET 4.0

  In the .NET Framework 3.5 SP1, Microsoft introduced ASP.NET Routing, which decouples the URL of a resource from the physical file on the web server. With ASP.NET Routing you, the developer, define routing rules map route patterns to a class that generates the content. For example, you might indicate that the URL Categories/CategoryName maps to a class that takes the CategoryName and generates HTML that lists that category's products in a grid. With such a mapping, users could view products for the Beverages category by visiting www.yoursite.com/Categories/Beverages. In .NET 3.5 SP1, ASP.NET Routing was primarily designed for ASP.NET MVC applications, although as discussed in Using ASP.NET Routing Without ASP.NET MVC it is possible to implement ASP.NET Routing in a Web Forms application, as well. However, implementing ASP.NET Routing in a Web Forms application involves a bit of seemingly excessive legwork. In a Web Forms scenario we typically want to map a routing pattern to an actual ASP.NET page. To do so we need to create a route handler class that is invoked when the routing URL is requested and, in a sense, dispatches the request to the appropriate ASP.NET page. For instance, to map a route to a physical file, such as mapping Categories/CategoryName to ShowProductsByCategory.aspx - requires three steps: (1) Define the mapping in Global.asax, which maps a route pattern to a route handler class; (2) Create the route handler class, which is responsible for parsing the URL, storing any route parameters into some location that is accessible to the target page (such as HttpContext.Items), and returning an instance of the target page or HTTP Handler that handles the requested route; and (3) writing code in the target page to grab the route parameters and use them in rendering its content. Given how much effort it took to just read the preceding sentence (let alone write it) you can imagine that implementing ASP.NET Routing in a Web Forms application is not necessarily the most straightforward task. The good news is that ASP.NET 4.0 has greatly simplified ASP.NET Routing for Web Form applications by adding a number of classes and helper methods that can be used to encapsulate the aforementioned complexity. With ASP.NET 4.0 it's easier to define the routing rules and there's no need to create a custom route handling class. This article details these enhancements. Read on to learn more! Read More >

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• ActAs and OnBehalfOf support in WIF

  - by cibrax

  I discussed a time ago how WIF supported a new WS-Trust 1.4 element, “ActAs”, and how that element could be used for authentication delegation.  The thing is that there is another feature in WS-Trust 1.4 that also becomes handy for this kind of scenario, and I did not mention in that last post, “OnBehalfOf”. Shiung Yong wrote an excellent summary about the difference of these two new features in this forum thread. He basically commented the following, “An ActAs RST element indicates that the requestor wants a token that contains claims about two distinct entities: the requestor, and an external entity represented by the token in the ActAs element. An OnBehalfOf RST element indicates that the requestor wants a token that contains claims only about one entity: the external entity represented by the token in the OnBehalfOf element. In short, ActAs feature is typically used in scenarios that require composite delegation, where the final recipient of the issued token can inspect the entire delegation chain and see not just the client, but all intermediaries to perform access control, auditing and other related activities based on the whole identity delegation chain. The ActAs feature is commonly used in multi-tiered systems to authenticate and pass information about identities between the tiers without having to pass this information at the application/business logic layer. OnBehalfOf feature is used in scenarios where only the identity of the original client is important and is effectively the same as identity impersonation feature available in the Windows OS today. When the OnBehalfOf is used the final recipient of the issued token can only see claims about the original client, and the information about intermediaries is not preserved. One common pattern where OnBehalfOf feature is used is the proxy pattern where the client cannot access the STS directly but is instead communicating through a proxy gateway. The proxy gateway authenticates the caller and puts information about him into the OnBehalfOf element of the RST message that it then sends to the real STS for processing. The resulting token is going to contain only claims related to the client of the proxy, making the proxy completely transparent and not visible to the receiver of the issued token.” Going back to WIF, “ActAs” and “OnBehalfOf” are both supported as extensions methods in the WCF client channel. public static class ChannelFactoryOperations {   public static T CreateChannelActingAs<T>(this ChannelFactory<T> factory,     SecurityToken actAs);     public static T CreateChannelOnBehalfOf<T>(this ChannelFactory<T> factory,     SecurityToken onBehalfOf); } Both methods receive the security token with the identity of the original caller.

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• Unstructured Data - The future of Data Administration

  Some have claimed that there is a problem with the way data is currently managed using the relational paradigm do to the rise of unstructured data in modern business. PCMag.com defines unstructured data as data that does not reside in a fixed location. They further explain that unstructured data refers to data in a free text form that is not bound to any specific structure. With the rise of unstructured data in the form of emails, spread sheets, images and documents the critics have a right to argue that the relational paradigm is not as effective as the object oriented data paradigm in managing this type of data. The relational paradigm relies heavily on structure and relationships in and between items of data. This type of paradigm works best in a relation database management system like Microsoft SQL, MySQL, and Oracle because data is forced to conform to a structure in the form of tables and relations can be derived from the existence of one or more tables. These critics also claim that database administrators have not kept up with reality because their primary focus in regards to data administration deals with structured data and the relational paradigm. The relational paradigm was developed in the 1970’s as a way to improve data management when compared to standard flat files. Little has changed since then, and modern database administrators need to know more than just how to handle structured data. That is why critics claim that today’s data professionals do not have the proper skills in order to store and maintain data for modern systems when compared to the skills of system designers, programmers , software engineers, and data designers  due to the industry trend of object oriented design and development. I think that they are wrong. I do not disagree that the industry is moving toward an object oriented approach to development with the potential to use more of an object oriented approach to data.   However, I think that it is business itself that is limiting database administrators from changing how data is stored because of the potential costs, and impact that might occur by altering any part of stored data. Furthermore, database administrators like all technology workers constantly are trying to improve their technical skills in order to excel in their job, so I think that accusing data professional is not just when the root cause of the lack of innovation is controlled by business, and it is business that will suffer for their inability to keep up with technology. One way for database professionals to better prepare for the future of database management is start working with data in the form of objects and so that they can extract data from the objects so that the stored information within objects can be used in relation to the data stored in a using the relational paradigm. Furthermore, I think the use of pattern matching will increase with the increased use of unstructured data because object can be selected, filtered and altered based on the existence of a pattern found within an object.

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