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  • What are practical guidelines for evaluating a language's "Turing Completeness"?

    - by AShelly
    I've read "what-is-turing-complete" and the wikipedia page, but I'm less interested in a formal proof than in the practical implications of being Turing Complete. What I'm actually trying to decide is if the toy language I've just designed could be used as a general-purpose language. I know I can prove it is if I can write a Turing machine with it. But I don't want to go through that exercise until I'm fairly certain of success. Is there a minimum set of features without which Turing Completeness is impossible? Is there a set of features which virtually guarantees completeness? (My guess is that conditional branching and a readable/writeable memory store will get me most of the way there) EDIT: I think I've gone off on a tangent by saying "Turing Complete". I'm trying to guess with reasonable confidence that a newly invented language with a certain feature set (or alternately, a VM with a certain instruction set) would be able to compute anything worth computing. I know proving you can building a Turing machine with it is one way, but not the only way. What I was hoping for was a set of guidelines like: "if it can do X,Y,and Z, it can probably do anything".

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  • How do I correctly model data in SQL-based databases that have some columns in common, but also have

    - by Brandon Weiss
    For instance, let's say I have a User model. Users have things like logins, passwords, e-mail addresses, avatars, etc. But there are two types of Users that will be using this site, let's say Parents and Businesses. I need to store some different information for the Parents (e.g. childrens' names, domestic partner, salaries, etc.) than for the Businesses (e.g. industry, number of employees, etc.), but also some of it is the same, like logins and passwords. How do I correctly structure this in a SQL-based database? Thanks!

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  • IList<Item> Collection Class accessing database

    - by Mike
    Hi, I have a database with Users. Users have Items. These Items can change actively. How do you access the items in a collection type format? For the user, I fill all the user properties at the time of instantiation. If I load the user's items at the time of the instantiation, and the items change, they will have old data. I was thinking, maybe I need an ItemCollection class and have that a field/property apart of the user class, that way to traverse all the user's items I could use a foreach loop. So, my question is, what is the best practice/best way of accessing the items from a database using some sort of collection? On accessing the particular Item, it needs to get the latest database information, and when the user does do a foreach loop, the latest item information must be available. I.e. What I'm trying to do Console.WriteLine(User.Items[3].ID); returns 5. //this updates the item information and saves it to the database. User.Items[3].ID = 13; //Add a new item to the database. User.Items.Add(new Item { id = 17}); foreach (Item item in User.Items) { //this would traverse all items in the database. //not some cached copy at the time of instantiation of the user. }

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  • Format for storing contacts in a database

    - by Gart
    I'm thinking of the best way to store personal contacts in a database for a business application. The traditional and straightforward approach would be to create a table with columns for each element, i.e. Name, Telephone Number, Job title, Address, etc... However, there are known industry standards for this kind of data, like for example vCard, or hCard, or vCard-RDF/XML or even Windows Contacts XML Schema. Utilizing an standard format would offer some benefits, like inter-operablilty with other systems. But how can I decide which method to use? The requirements are mainly to store the data. Search and ordering queries are highly unlikely but possible. The volume of the data is 100,000 records at maximum. My database engine supports native XML columns. I have been thinking to use some XML-based format to store the personal contacts. Then it will be possible to utilize XML indexes on this data, if searching and ordering is needed. Is this a good approach? Which contacts format and schema would you recommend for this?

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  • Subversion Repository Layout

    - by Tim Long
    Most subversion tools create a default repository layout with /trunk, /branches and /tags. The documentation also recommends not using separate repositories for each project, so that code can be more easily shared. Following that advice has led to me having a repository with the following layout: /trunk /Project1 /Project2 /branches /Project1 /Project2 /tags /Project1 /Project2 and so on, you get the idea. Over time, I've found this structure a bit clumsy and it occurred to me that there's an alternative interpretation of the recommendations, such as: /Project1 /trunk /branches /tags /Project2 /trunk /branches /tags So, which layout do people use, and why? Or - is there another way to do things that I've completely missed?

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  • Coding without Grock. Is it wrong?

    - by OldCurmudgeon
    Should a professional programmer allow themselves to write code without completely understanding the requirements? In my 30+ years as a programmer I must have written many thousands of lines of code without completely understanding what is required of me at the time. In most cases the results were rubbish that should have been discarded. Every other industry that employs professionals has systems to root out such behavior. Ours does not. Is this right?

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  • how relate one table to another for future records

    - by Sinan
    I have a games table which holds the data about a game. Then another table which holds the data about news. So far so good. First I thought about creating a junction table for game_news so I could relate news to games. This way works as intended when the game exists. So whenever I insert a news I can relate it to a game using the junction table. However there are cases when there is news about game but the game isn't published and it doesn't exists. So my question would be; is there a way to relate these news to a particular game when the game record is created. What is the best way to do this? Any ideas?

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  • Database access through collections

    - by Mike
    Hi All, I have an 3 tiered application where I need to get database results and populated the UI. I have a MessagesCollection class that deals with messages. I load my user from the database. On the instantiation of a user (ie. new User()), a MessageCollection Messages = new MessageCollection(this) is performed. Message collection accepts a user as a parameter. User user = user.LoadUser("bob"); I want to get the messages for Bob. user.Messages.GetUnreadMessages(); GetUnreadMessages calls my Business Data provider which in turn calls the data access layer. The Business data provider returns List. My question is - I am not sure what the best practice is here - If I have a collection of messages in an array inside the MessagesCollection class, I could implement ICollection to provide GetEnumerator() and ability to traverse the messages. But what happens if the messages change and the the user has old messages loaded? What about big message collections? What if my user had 10,000 unread messages? I don't think accessing the database and returning 10,000 Message objects would be efficient.

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  • Why are alloc and init called separately in Objective-C?

    - by André Hoffmann
    Note: I'm relatively new to Objective-C and am coming from Java and PHP. Could someone explain to me why I always have to first allocate and then initialize an instance? Couldn't this be done in the init methods like this: + (MyClass*)init { MyClass *instance = [MyClass alloc]; [instance setFoo:@"bla"]; return instance; } + (MyClass*)initWithString:(NSString*)text { MyClass *instance = [MyClass init]; [instance setFoo:text]; return instance; } ... Is this just a relict from the old C days or is there something that I'm not seeing? I know this isn't a problem as I could as well always call alloc and init, but since it's a bit tedious I'd like to at least know why I'm doing it. I'm liking the expressiveness of the language so far, but this is something that I want to fully understand in order to think the Objective-C way. Thank you!

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  • To Wrap or Not to Wrap: Wrapping Data Access in a Service Facade

    - by PureCognition
    For a while now, my team and I have been wrapping our data access layer in a web service facade (using WCF) and calling it from the business logic layer. Meanwhile, we could simply use the repository pattern where the business logic layer consumes the data access layer locally through an interface, and at any point in time, we can switch things out for it to hit a service instead (if necessary). The question is: When is it a good time to wrap the data access layer in a service facade and when isn't it? Right now, it seems like the main advantage is that other applications can consume the service, but if they are internal applications written in .NET then they can just consume the .NET assembly instead. Are there other advantages of having the DAL be wrapped in a service that I am unaware of?

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  • How does a WCF server inform a WCF client about changes? (Better solution then simple polling, e.g.

    - by Ian Ringrose
    see also "WCF push to client through firewall" I need to have a WCF client that connect to a WCF server, then when some of the data changes on the server the clients need to update its display. As there is likely to be a firewall between the clients and the server. All communications must be over HTTP The server can not make an (physical) outgoing call to the client. As I am writing both the client and the server I do not need to limit the solution to only using soap etc. I am looking for built in surport for "long polling" / "Comet" etc Thanks for the most informative answer from Drew Marsh on how to implement long polling in WCF. However I thought the main “selling point” of WCF was that you could do this sort of thing just by configuring the channels to be used in the config file. E.g I want a channel that logically two way but physically incoming only.

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  • Function overloading by return type?

    - by dsimcha
    Why don't more mainstream statically typed languages support function/method overloading by return type? I can't think of any that do. It seems no less useful or reasonable than supporting overload by parameter type. How come it's so much less popular?

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  • Pattern/Matcher in Java?

    - by user1007059
    I have a certain text in Java, and I want to use pattern and matcher to extract something from it. This is my program: public String getItemsByType(String text, String start, String end) { String patternHolder; StringBuffer itemLines = new StringBuffer(); patternHolder = start + ".*" + end; Pattern pattern = Pattern.compile(patternHolder); Matcher matcher = pattern.matcher(text); while (matcher.find()) { itemLines.append(text.substring(matcher.start(), matcher.end()) + "\n"); } return itemLines.toString(); } This code works fully WHEN the searched text is on the same line, for instance: String text = "My name is John and I am 18 years Old"; getItemsByType(text, "My", "John"); immediately grabs the text "My name is John" out of the text. However, when my text looks like this: String text = "My name\nis John\nand I'm\n18 years\nold"; getItemsByType(text, "My", "John"); It doesn't grab anything, since "My" and "John" are on different lines. How do I solve this?

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  • Star-schema: Separate dimensions for clients and non-clients or shared dimension for attendants?

    - by celopes
    I'm new to modeling star schemas, fresh from reading the Data Warehouse Toolkit. I have a business process that has clients and non-clients calling into conference calls with some of our employees. My fact table, call it "Audience", will contain a measure of how long an attending person was connected to the call, and the cost per minute of this person's connection to the call. The grain is "individual connection to the conference call". Should I use my conformed Client dimension and create a non-client dimension (for the callers that are not yet clients) this way (omitting dimensions that are not part of this questions): Or would it be OK/better to have a non-conformed Attending dimension related to the conformed Client dimension in this manner: Or is there a better/standard mechanism to model business processes like this one?

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  • Looking for some thoughts on an image printing app

    - by Alex
    Hey All, Im looking for thoughts/advice. I have an upcoming project (all .net) that will require the following: pulls data once a day from an online service provider based on certain criteria. saves data locally for reference and reporting the data thats pulled will be used to create gift cards. So after the data is loaded, a process will run to generate "virtual cards" and send them to a network printer. Once printed, the system will updated the local data recording a successful or failed print. My initial thought was to create a windows service to pull the data...but then I couldnt decide how I was going to put a "virtual card" together and get it to print. Then I considered doing it as a WPF app. I figure that will give me access to the graphics and printing ability. Maybe neither of these are the right direction....Any ideas or thoughts would be greatly appreciated. Alex

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  • Communication between modules

    - by David Elentok
    I have an application that consists from the following three modules: Search (to search for objects) List (to display the search results) Painter (to allow me to edit objects) - this module isn't always loaded (Each object is a figure that I can edit in the painter). When I open an object in the painter it's added to the objects that are already in the painter and I can move it and alter it. I'm using an object similar to the EventAggregator to communicate between the modules. For example, to show the search results I publish a "ShowList" event that is caught by the List module (I'm not sure this is the best way to do this, if anyone has better idea please comment...). One of the features of the search module requires it to get the selected object in the painter (if the painter is available), and I'm not sure what would be the best way to do that... I thought of these solutions: Whenever the selected object in the painter changes it will publish a "PainterSelectedObjectChanged" event which will be caught by the search module and stored for later use. When the selected object is needed by the search module it will publish a "RequestingPainterSelectedObject" event which will be caught by the painter module. The painter module will then set the "SelectedObject" property in the EventArgs object, and when the publish is complete and we're back in the search module we will have the painter's selected object in the EventArgs object. What do you think? what is the right way to do this?

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  • Discover periodic patterns in a large data-set

    - by Miner
    I have a large sequence of tuples on disk in the form (t1, k1) (t2, k2) ... (tn, kn) ti is a monotonically increasing timestamp and ki is a key (assume a fixed length string if needed). Neither ti nor ki are guaranteed to be unique. However, the number of unique tis and kis is huge (millions). n itself is very large (100 Million+) and the size of k (approx 500 bytes) makes it impossible to store everything in memory. I would like to find out periodic occurrences of keys in this sequence. For example, if I have the sequence (1, a) (2, b) (3, c) (4, b) (5, a) (6, b) (7, d) (8, b) (9, a) (10, b) The algorithm should emit (a, 4) and (b, 2). That is a occurs with a period of 4 and b occurs with a period of 2. If I build a hash of all keys and store the average of the difference between consecutive timestamps of each key and a std deviation of the same, I might be able to make a pass, and report only the ones that have an acceptable std deviation(ideally, 0). However, it requires one bucket per unique key, whereas in practice, I might have very few really periodic patterns. Any better ways?

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  • Java Polymorphism - Selecting correct method based on subtype

    - by Marty Pitt
    Hi Given the following Class and Service layer signatures: public class PersonActionRequest { PersonVO person // ... other fields } public class MyServiceLayerClass { public void requestAction(PersonActionRequest request) { PersonVO abstractPerson = request.getPerson(); // call appropriate executeAction method based on subclass of PersonVO } private void executeAction(PersonVO person) {} private void executeAction(EmployeeVO employee) {} private void executeAction(ManagerVO manager) {} private void executeAction(UnicornWranglerVO unicornWrangler) {} } As discussed here, java will select the best method based on type info at compile time. (Ie., it will always select executeAction(PersonVO person) ). What's the most appropriate way to select the correct method? The internet tells me that using instanceof gets me slapped. However, I don't see the appropraite way to select the method without explictly casting abstractPerson to one of the other concrete types. Thanks Marty

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  • Best Practice for Utilities Class?

    - by Sonny Boy
    Hey all, We currently have a utilities class that handles a lot of string formatting, date displays, and similar functionality and it's a shared/static class. Is this the "correct" way of doing things or should we be instanciating the utility class as and when we need it? Our main goal here is to reduce memory footprint but performance of the application is also a consideration. Thanks, Matt PS. We're using .NET 2.0

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  • When to release the model(representedObject) of the corresponding UIViewController.

    - by user313786
    Hi, In AppKit we have "representedObject" available through NSViewController, this representedObject is generally set to ModelController or the model which the NSViewController displays, this works great with bindings as you just set the new representedObject and model details are updated in the view, BUT in case of iPhone (UIKit, with NO Cocoa bindings available), there is no such representedObject in UIViewController so here are few things I am interested in knowing:- What is the best/recommended way of binding the model to the UIViewController?, preferably dont want to maintain lot of IBOutlets and calls setters to updated the changed model data for display in view. How/When should the related model of the UIViewController be released? When is the -[UIViewController dealloc] called, in the typical iPhone application. Am looking for architecting some classes so that the UIViewController coordinates between the view and the model, but at the same time, deallocs the model when ever not necessary. TIA.

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  • How my Website looks like under Different Screen Resolutions?

    - by strakastroukas
    Back in the past, i found a third party webpage that was able to capture and save images of my website in different resolutions and browsers. Of course i have no more that bookmark... So is there any webpage or application where i can see how my webpage looks like in different resolution? And here are the resolutions i would like to check for... 1. 1024x768 24.56% 2. 1280x800 22.06% 3. 1280x1024 13.42% 4. 1366x768 7.10% 5. 1440x900 6.68%

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