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• Recognizing terminals in a CFG production previously not defined as tokens.

  - by kmels

  I'm making a generator of LL(1) parsers, my input is a CoCo/R language specification. I've already got a Scanner generator for that input. Suppose I've got the following specification: COMPILER 1. CHARACTERS digit="0123456789". TOKENS number = digit{digit}. decnumber = digit{digit}"."digit{digit}. PRODUCTIONS Expression = Term{"+"Term|"-"Term}. Term = Factor{"*"Factor|"/"Factor}. Factor = ["-"](Number|"("Expression")"). Number = (number|decnumber). END 1. So, if the parser generated by this grammar receives a word "1+1", it'd be accepted i.e. a parse tree would be found. My question is, the character "+" was never defined in a token, but it appears in the non-terminal "Expression". How should my generated Scanner recognize it? It would not recognize it as a token. Is this a valid input then? Should I add this terminal in TOKENS and then consider an error routine for a Scanner for it to skip it? How does usual language specifications handle this?

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• Can games be considered real-time systems?

  - by harry

  I've been reading up on real-time systems and how they work etc. I was looking at the wikipedia article as well that said a game of Chess with a timer per move can be considered a real-time system because the program MUST compute a move in that time. What about other games? As we know, games generally try and run at 25+ FPS, could it be considered a soft real-time system since if it falls under 25 (I'm using 25 as a pre-defined threshold btw) it's not the end of the world, just a hit to the performance that we wanted? Also - games have events they must handle as well. The user uses the keyboard/mouse and the system must answer those events accordingly within (again) a pre-defined time, before the game is considered to have "failed". Oh, and I'm talking single-player for now to keep things simple. It sounds like games fit the soft real-time system criteria, but I'd like to know if I'm missing anything... thanks.

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• .NET How would I build a DAL to meet my requirments?

  - by Jonno

  Assuming that I must deploy an asp.net app over the following 3 servers: 1) DB - not public 2) 'middle' - not public 3) Web server - public I am not allowed to connect from the web server to the DB directly. I must pass through 'middle' - this is purely to slow down an attacker if they breached the web server. All db access is via stored procedures. No table access. I simply want to provide the web server with a ado dataset (I know many will dislike this, but this is the requirement). Using asmx web services - it works, but XML serialisation is slow and it's an extra set of code to maintain and deploy. Using a ssh/vpn tunnel so that the one connects to the db 'via' the middle server, seems to remove any possible benefit of maintaining 'middle'. Using WCF binary/tcp removes the XML problem, but still there is extra code. Is there an approach that provides the ease of ssh/vpn, but the potential benefit of having the dal on the middle server? Many thanks.

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• Application Buddy Lists and Authentication - How does it all go together

  - by Krevin

  This is a broad but specific question. The idea is that we want to tie in a 'buddy' functionality to a communications app. Very broadly, I believe that the application clients would connect to a central database/auth service which would provide the buddy data and then allow client apps to connect directly to eachother, without passing communications through the server. Specifically, however, what solutions, software, products, servers, technologies, etc would be best to implement to handle such a task? Thanks for reading and responses are much appreciated. //edit: the com app may run on a linux distro, may be web based, or both

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• Fluent NHibernate SchemaExport to SQLite not pluralizing Table Names

  - by weenet

  I am using SQLite as my db during development, and I want to postpone actually creating a final database until my domains are fully mapped. So I have this in my Global.asax.cs file: private void InitializeNHibernateSession() { Configuration cfg = NHibernateSession.Init( webSessionStorage, new [] { Server.MapPath("~/bin/MyNamespace.Data.dll") }, new AutoPersistenceModelGenerator().Generate(), Server.MapPath("~/NHibernate.config")); if (ConfigurationManager.AppSettings["DbGen"] == "true") { var export = new SchemaExport(cfg); export.Execute(true, true, false, NHibernateSession.Current.Connection, File.CreateText(@"DDL.sql")); } } The AutoPersistenceModelGenerator hooks up the various conventions, including a TableNameConvention like so: public void Apply(FluentNHibernate.Conventions.Instances.IClassInstance instance) { instance.Table(Inflector.Net.Inflector.Pluralize(instance.EntityType.Name)); } This is working nicely execpt that the sqlite db generated does not have pluralized table names. Any idea what I'm missing? Thanks.

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• Is there a simple, safe way to trigger a GPU lockup on a susceptible computer?

  - by Abe

  Answers to my previous question, Ubuntu 12.04 froze, requiring powercycle. What should I look / grep for in the logs?, have led me to suspect that my computer is experiencing an intermittent GPU lockup. It has been happening about once a week, usually when I am using Chrome. Today it happened when I was creating a diagram on lucidchart I have a Dell Optiplex 755 with an ATI Radeon HD 2400 XT and dual monitors running in Xinerama mode. I am using 12.04 with the proprietary ATI driver installed. When the computer locks-up, I can still ssh in. And I would like to follow the instructions on reporting this provided at https://wiki.ubuntu.com/X/Troubleshooting/Freeze Is there a (safe) way to cause a GPU lockup so that I can go ahead and file a bug, rather than waiting until it happens again?

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• What is the best approach for creating a Common Information Model?

  - by Kaiser Advisor

  Hi, I would like to know the best approach to create a Common Information Model. Just to be clear, I've also heard it referred to as a canonical information model, semantic information model, and master data model - As far as I can tell, they are all referring to the same concept. I've heard in the past that a combined "top-down" and "bottom-up" approach is best. This has the advantage of incorporating "Ivory tower" architects and developers - The work will meet somewhere in the middle and usually be both logical and practical. However, this involves bringing in a lot of people with different skill sets. I've also seen a couple of references to the Distributed Management Task Force, but I can't glean much on best practices in terms of CIM development. This is something I'm quite interested in getting some feedback on since having a strong CIM is a prerequisite to SOA. Thanks for your help! KA Update I've heard another strategy goes along with overall SOA implementation: Get the business involved, and seek executive sponsorship. This would be part of the "Top-down" effort.

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• Help with Event-Based Components

  - by Joel in Gö

  I have started to look at Event-Based Components (EBCs), a programming method currently being explored by Ralf Wesphal in Germany, in particular. This is a really interesting and promising way to architect a software solution, and gets close to the age-old idea of being able to stick software components together like Lego :) A good starting point is the Channel 9 video here, and there is a fair bit of discussion in German at the Google Group on EBCs. I am however looking for more concrete examples - while the ideas look great, I am finding it hard to translate them into real code for anything more than a trivial project. Does anyone know of any good code examples (in C# preferably), or any more good sites where EBCs are discussed?

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• What considerations should be made for a web app to be released on a cloud hosted system?

  - by Rhubarb

  I have a web app that is primarily a WordPress app, but it pulls content from a Django app, simply by calling a service that uses Django models. My understanding of cloud computing is a bit vague. If the site needs to scale up with short notice, does the cloud provider (Amazon, Rackspace, whomever) simply spin up new instances (copies) of my initially configured server? How is state managed between all of them? Are there any good primers on this subject? It's hard to find much out there without getting caught up in the marketing.

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• Separate functionality depending on Role in ASP.NET MVC

  - by Andrew Bullock

  I'm looking for an elegant pattern to solve this problem: I have several user roles in my system, and for many of my controller actions, I need to deal with slightly different data. For example, take /Users/Edit/1 This allows a Moderator to edit a users email address, but Administrators to edit a user's email address and password. I'd like a design for separating the two different bits of action code for the GET and the POST. Solutions I've come up with so far are: Switch inside each method, however this doesn't really help when i want different model arguments on the POST :( Custom controller factory which chooses a UsersController_ForModerators and UsersController_ForAdmins instead of just UsersController from the controller name and current user role Custom action invoker which choose the Edit_ForModerators method in a similar way to above Have an IUsersController and register a different implementation of it in my IoC container as a named instance based on Role Build an implementation of the controller at runtime using Castle DynamicProxy and manipulate the methods to those from role-based implementations Im preferring the named IoC instance route atm as it means all my urls/routing will work seamlessly. Ideas? Suggestions?

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• Distributed Message Ordering

  - by sbanwart

  I have an architectural question on handling message ordering. For purposes of this question, the transport is irrelevant, so I'm not going to specify one. Say we have three systems, a website, a CRM and an ERP. For this example, the ERP will be the "master" system in terms of data ownership. The website and the CRM can both send a new customer message to the ERP system. The ERP system then adds a customer and publishes the customer with the newly assigned account number so that the website and CRM can add the account number to their local customer records. This is a pretty straight forward process. Next we move on to placing orders. The account number is required in order for the CRM or website to place an order with the ERP system. However the CRM will permit the user to place an order even if the customer lacks an account number. (For this example assume we can't modify the CRM behavior) This creates the possibility that a user could create a new customer, and place an order before the account number gets updated in the CRM. What is the best way to handle this scenario? Would it be best to send the order message sans account number and let it go to an error queue? Would it be better to have the CRM endpoint hold the message and wait until the account number is updated in the CRM? Maybe something completely different that I haven't thought of? Thanks in advance for any help.

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• Does using web services to expose a .NET DAL add security?

  - by Jonno

  Currently my employer deploys a web application over 3 servers. DB - No public route Web Service DAL - No public route Web Server - Public route The reason for this is the theory that if the web server is compromised, they don't arrive at the DB directly, but instead arrive at the DAL box. To my mind, as the DAL box and Web Sever box - both run windows/IIS - if the public box has been compromised, the same exploit would likely work on the DAL box - therefore I do not see this as a real security benefit. I would like to propose we remove the middle machine and allow the web server to connect directly to the database. Is this middle box really a benefit?

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• How do I dismiss an NSPanel when creating or opening a new document?

  - by mipadi

  I am working on a document-based Cocoa application. At startup, the user is presented with a "welcome panel" (of type NSPanel) with buttons for common actions like "Create New Document" and "Open Existing Document". These actions are linked to the first responder's newDocument: and openDocument: actions, respectively, just like the matching items in the File menu. Everything works as expected...with two caveats: The welcome panel is not dismissed when creating or opening a new document. Document windows do not have focus when they are created. I have partially solved #1 by making my application controller a delegate of the welcome panel. When clicking the "Open Existing Document" button, the panel resigns its key status (since a file browser dialog is being opened), so I can close the panel in the delegate's windowDidResignKey: method. However, I can't figure out how to close the panel when creating a new document, since I can't find a notification that is posted, or a delegate method that is called, when creating a new document. And ultimately, #2 is still a problem, since the document windows don't gain focus when they're created. I have only subclassed NSDocument -- I'm not using a custom document or window controller at all. I've also tried changing the panel to an NSWindow, thinking that an NSWindow may behave differently, but the same problems are occurring.

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• Is there any reason for an object pool to not be treated as a singleton?

  - by Chris Charabaruk

  I don't necessarily mean implemented using the singleton pattern, but rather, only having and using one instance of a pool. I don't like the idea of having just one pool (or one per pooled type). However, I can't really come up with any concrete situations where there's an advantage to multiple pools for mutable types, at least not any where a single pool can function just as well. What advantages are there to having multiple pools over a singleton pool?

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• Pros and Cons on where to place business logic: app level or DB

  - by Juri

  Hi, I always again encounter discussions about where to place the business logic: inside a business layer in the application code or down in the DB in terms of stored procedures. Personally I'd tend to the 1st approach, but I'd like to hear some opinions from your part first, without influencing you with my personal views. I know there doesn't exist a one-size-fits-all solution and it often depends on many factors, but we can discuss about that. Btw, we are in the context of web applications and our current approach is to have UI layer which accepts UI input and does a first, client-side validation Business layer with a number of service-classes which contains the business logic including validation for user input (server-side) Data Access Layer which calls stored procedures from the DB for doing persistency/read operations Many people however tend to move the business layer stuff (especially regarding the validation) down to the DB in terms of stored procedures. What do you think about it? I'd like to discuss.

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• ASP.NET sets of technologies/components

  - by Maxim Gueivandov

  Just a question of pure curiosity. It happens that development teams tend to stick to the same technological set(s) for some time, for various reasons (obviously, the lack of time, money, necessity and/or willingless to adopt new technologies). So, what are your usual sets of technologies/components to build an ASP.NET application (e.g., WebForms / MVC, Automapper, NInject, NHibernate / LinqToSql, JQuery / ASP.NET Ajax, ...) or architectural frameworks (Arch#, Catharsis, ...) and in which context do you use them (site size, speed/availability requirements, etc.)?

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• Architectural decision : QT or Eclipse Platform ?

  - by umanga

  We are in the process of designing a tool to be used with HDEM(High Definition Electron Microscope).We get stacks of 2D images from HDEM and first step is 'detecting borders' on the sections.After detecting edges of 2D slices ,next step is construct the 3D model using these 2D slices. This 'border detecting' algorithm(s) is/are implemented by one of professor and he has used and suggests to use C.(to gain high performance and probably will parallelise in future) We have to develop comprehensive UI ,3D viewer ,2D editor...etc and use this algorithm. Application should support usual features like project save/open.Undo,Redo...etc Our technology decisions are: A) Build entire platform from the scratch using QT. B) Use Eclipse Platform Our concerns are, if we choose A) we can easily integrate the 'border detecting' algorithm(s) because the development environment is C/C++ But we have to implement the basic features from the scratch. If we choose B) we get basic features from the Eclipse platform , but integrating C libraries going to be a tedious task. Any suggestions on this?

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• recursion tree and binary tree cost calculation

  - by Tony

  Hi all, I've got the following recursion: T(n) = T(n/3) + T(2n/3) + O(n) The height of the tree would be log3/2 of 2. Now the recursion tree for this recurrence is not a complete binary tree. It has missing nodes lower down. This makes sense to me, however I don't understand how the following small omega notation relates to the cost of all leaves in the tree. "... the total cost of all leaves would then be Theta (n^log3/2 of 2) which, since log3/2 of 2 is a constant strictly greater then 1, is small omega(n lg n)." Can someone please help me understand how the Theta(n^log3/2 of 2) becomes small omega(n lg n)?

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• When are you truly forced to use UUID as part of the design?

  - by Pyrolistical

  I don't really see the point of UUID. I know the probability of a collision is effectively nil, but effectively nil is not even close to impossible. Can somebody give an example where you have no choice but to use UUID? From all the uses I've seen, I can see an alternative design without UUID. Sure the design might be slightly more complicated, but at least it doesn't have a non-zero probability of failure. UUID smells like global variables to me. There are many ways global variables make for simpler design, but its just lazy design.

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• Can NHibernate tell me which properties of an object have changed?

  - by zoman

  Is it possible to find out what has changed when an object has been updated in Nhibernate? Thanks.

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• 32 vs 64 bit...or, what exactly does 'processing information' mean

  - by jasonbogd

  I am having trouble understanding the difference between a 32 bit processor and 64 bit processor. I know that a 32 bit processor can access 32 bits at a time while a 64 bit processor can access 64 bits at a time. But what exactly does it mean to access a certain number of bits at one time?

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• How can i use complextype class or multi type class is it generic collection?

  - by programmerist

  i need a complex returning type. i have 4 class returning types COMPLEXTYPE must include Company, Muayene, Radyoloji, Satis because i must return data switch case situation how can i do? Maybe i need generic collections How can i do that? public class GenoTipController { public COMPLEXTYPE Generate(DataModelType modeltype) { _Company company = null; _Muayene muayene = null; _Radyoloji radyoloji = null; _Satis satis = null; switch (modeltype) { case DataModelType.Radyoloji: radyoloji = new Radyoloji(); return radyoloji; break; case DataModelType.Satis: satis = new Satis(); return satis; break; case DataModelType.Muayene: muayene = new Muayene(); return muayene; break; case DataModelType.Company: company = new Company(); return company; break; default: break; } } } public class CompanyView { public static List GetPersonel() { GenoTipController controller = new GenoTipController(); _Company company = controller.Generate(DataModelType.Company); return company.GetPersonel(); } } public enum DataModelType { Radyoloji, Satis, Muayene, Company }

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• Algorithm for optimally choosing actions to perform a task

  - by Jules

  There are two data types: tasks and actions. An action costs a certain time to complete, and a set of tasks this actions consists of. A task has a set of actions, and our job is to choose one of them. So: class Task { Set<Action> choices; } class Action { float time; Set<Task> dependencies; } For example the primary task could be "Get a house". The possible actions for this task: "Buy a house" or "Build a house". The action "Build a house" costs 10 hours and has the dependencies "Get bricks" and "Get cement", etcetera. The total time is the sum of all the times of the actions required to perform. We want to choose actions such that the total time is minimal. Note that the dependencies can be diamond shaped. For example "Get bricks" could require "Get a car" (to transport the bricks) and "Get cement" would also require a car. Even if you do "Get bricks" and "Get cement" you only have to count the time it takes to get a car once. Note also that the dependencies can be circular. For example "Money" - "Job" - "Car" - "Money". This is no problem for us, we simply select all of "Money", "Job" and "Car". The total time is simply the sum of the time of these 3 things. Mathematical description: Let actions be the chosen actions. valid(task) = ?action ? task.choices. (action ? actions ? ?tasks ? action.dependencies. valid(task)) time = sum {action.time | action ? actions} minimize time subject to valid(primaryTask)

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• Core principles, rules, and habits for CS students

  - by Asad Butt

  No doubt there is a lot to read on blogs, in books, and on Stack Overflow, but can we identify some guidelines for CS students to use while studying? For me these are: Finish your course books early and read 4-5 times more material relative to your course work. Programming is the one of the fastest evolving professions. Follow the blogs on a daily basis for the latest updates, news, and technologies. Instead of relying on assignments and exams, do at least one extra, non-graded, small to medium-sized project for every programming course. Fight hard for internships or work placements even if they are unpaid, since 3 months of work 1 year at college. Practice everything, every possible and impossible way. Try doing every bit of your assignments project yourself; i.e. fight for every inch. Rely on documentation as the first source for help and samples, Google, and online forums as the last source. Participate often in online communities and forums to learn the best possible approach for every solution to your problem. (After doing your bit.) Make testing one of your habits as it is getting more important everyday in programming. Make writing one of your habits. Write something productive once or twice a week and publish it.

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• Opaque tenant identification with SQL Server & NHibernate

  - by Anton Gogolev

  Howdy! We're developing a nowadays-fashionable multi-tenanted SaaS app (shared database, shared schema), and there's one thing I don't like about it: public class Domain : BusinessObject { public virtual long TenantID { get; set; } public virtual string Name { get; set; } } The TenantID is driving me nuts, as it has to be accounted for almost everywhere, and it's a hassle from security standpoint: what happens if a malicious API user changes TenantID to some other value and will mix things up. What I want to do is to get rid of this TenantID in our domain objects altogether, and to have either NHibernate or SQL Server deal with it. From what I've already read on the Internets, this can be done with CONTEXT_INFO (here's a NHibernatebased implementation), NHibernate filters, SQL Views and with combination thereof. Now, my requirements are as follows: Remove any mentions of TenantID from domain objects ...but have SQL Server insert it where appropriate (I guess this is achieved with default constraints) ...and obviously provide support for filtering based on this criteria, so that customers will never see each other's data If possible, avoid SQL Server views. Have a solution which plays nicely with NHibernate, SQL Servers' MARS and general nature of SaaS apps being highly concurrent What are your thoughts on that?

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