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  • OpenSource license with commerial-use exemptions for the owner

    - by dbkk
    I'm looking for an open source license which grants me additional privileges. Features: Anyone can freely modify, fork, use the code, as long as they make their source changes publicly available. They can use it in other open source projects, but not in closed-source projects. Only I and entities I specifically designate can use the code as part of a closed-source application. I am also exempt from the duty to publish the source code changes. I'm not trying to forbid the commercial use, just to allow myself more flexibility to use the code, while still contributing to open source. I don't want to burn myself by being legally forbidden from using the libraries I wrote in my commercial projects. Large companies use such dual licenses to maintain an open source project, while also selling the premium version. Which licenses of this type are available? What caveats or obstacles exist?

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  • Are microsoft certificates useful [closed]

    - by grabah
    Possible Duplicate: Why should you get MCTS certified? Are microsoft certificates useful for anything more than beeing a bonus on job interviews? I do believe in formal training but i'm sceptical about their value, specialy if i dont' take classes (not enough time/money) but study at home/online and than go directly to take exams. Would you recomend taking preparation classes, or are they just waste of time? (or perhaps is whole certification thing waste of time?) (i have several years of expirience and currently working in software development)

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  • Groovy/Grails course content

    - by Don
    Hi, Some Java developers have asked if I could give them a 2-day primer on Grails development. I'm assuming they're familiar with: Java language and libraries Java web development, e.g. Servlets, JSPs Spring Hibernate Client-side development, CSS, HTML, JavaScript I'm further assuming they have no experience with Groovy or Grails. AFAIK, the app that they'll be building is a new project, so there's no need to cover topics like using GORM with a legacy database. I'm trying to decide how I should structure the course, e.g. what topics to cover and how much time to spend on each. I reckon about 1/2 - 3/4 days on Groovy and the rest of the time on Grails would be adequate. I'll probably use the Groovy console to demonstrate the Groovy language concepts and a simple Grails app for explaining the conventions and structure of a Grails project. If anyone has a list of Groovy/Grails topics that I should cover, or even an outline of a similar course that they've given/taken, I'd be very grateful. Naturally, I will credit for any resources that I use during the course.

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  • Layout of mathematical views (iOS)

    - by William Jockusch
    I am trying to figure out the right way to encapsulate graphical information about mathematical objects. It is not simple. For example, a matrix can include square brackets around its entries, or not. Some things carry down to sub-objects -- for example, a matrix might track the font size to be used by its entries. Similarly, the font color and the background color would carry down to the entries. Other things do not carry down. For example, the entries of the matrix do not need to know whether or not the matrix has those square brackets. Based on all of the above, I need to calculate sizes for everything, then frames. All of this can depend on the properties stored above. The size of a matrix depends on the sizes of its entries, and also on whether or not it has those brackets. What I am having a hard time with is not the individual ways to calculate sensible frames for this or that. It is the overall organizational structure of the whole thing. How can I keep track of it all without going crazy. One particular obstacle is worth mentioning -- for reasons I don't want to go into here, I need to calculate the sizes and frames for everything before I instantiate any actual views. So, for example, if I have a Matrix object, I need to calculate its size before I make a MatrixView. If I have an equation, I need to calculate the size of the view for the equation before I create the actual view. So I clearly need separate objects for those calculations. But I can't figure out a sensible class structure for those objects. If I put them all into a single class, I get some advantages because copying then becomes easy. But I also end up with a bloated class that contains info that is irrelevant for some objects -- such as whether or not to include those brackets around the matrix. But if I use a lot of different classes, copying properties becomes a real pain. If it matters, this is all in Objective C, for an iOS environment. Any pointers would be greatly appreciated.

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  • Should a server "be lenient" in what it accepts and "discard faulty input silently"?

    - by romkyns
    I was under the impression that by now everyone agrees this maxim was a mistake. But I recently saw this answer which has a "be lenient" comment upvoted 137 times (as of today). In my opinion, the leniency in what browsers accept was the direct cause of the utter mess that HTML and some other web standards were a few years ago, and have only recently begun to properly crystallize out of that mess. The way I see it, being lenient in what you accept will lead to this. The second part of the maxim is "discard faulty input silently, without returning an error message unless this is required by the specification", and this feels borderline offensive. Any programmer who has banged their head on the wall when something fails silently will know what I mean. So, am I completely wrong about this? Should my program be lenient in what it accepts and swallow errors silently? Or am I mis-interpreting what this is supposed to mean? The original question said "program", and I take everyone's point about that. It can make sense for programs to be lenient. What I really meant, however, is APIs: interfaces exposed to other programs, rather than people. HTTP is an example. The protocol is an interface that only other programs use. People never directly provide the dates that go into headers like "If-Modified-Since". So, the question is: should the server implementing a standard be lenient and allow dates in several other formats, in addition to the one that's actually required by the standard? I believe the "be lenient" is supposed to apply to this situation, rather than human interfaces. If the server is lenient, it might seem like an overall improvement, but I think in practice it only leads to client implementations that end up relying on the leniency and thus failing to work with another server that's lenient in slightly different ways. So, should a server exposing some API be lenient or is that a very bad idea? Now onto lenient handling of user input. Consider YouTrack (a bug tracking software). It uses a language for text entry that is reminiscent of Markdown. Except that it's "lenient". For example, writing - foo - bar - baz is not a documented way of creating a bulleted list, and yet it worked. Consequently, it ended up being used a lot throughout our internal bugtracker. Next version comes out, and this lenient feature starts working slightly differently, breaking a bunch of lists that (mis)used this (non)feature. The documented way to create bulleted lists still works, of course. So, should my software be lenient in what user inputs it accepts?

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  • Masters vs. PhD - long [closed]

    - by Sterling
    I'm 21 years old and a first year master's computer science student. Whether or not to continue with my PhD has been plaguing me for the past few months. I can't stop thinking about it and am extremely torn on the issue. I have read http://www.cs.unc.edu/~azuma/hitch4.html and many, many other masters vs phd articles on the web. Unfortunately, I have not yet come to a conclusion. I was hoping that I could post my ideas about the issue on here in hopes to 1) get some extra insight on the issue and 2) make sure that I am correct in my assumptions. Hopefully having people who have experience in the respective fields can tell me if I am wrong so I don't make my decision based on false ideas. Okay, to get this topic out of the way - money. Money isn't the most important thing to me, but it is still important. It's always been a goal of mine to make 6 figures, but I realize that will probably take me a long time with either path. According to most online salary calculating sites, the average starting salary for a software engineer is ~60-70k. The PhD program here is 5 years, so that's about 300k I am missing out on by not going into the workforce with a masters. I have only ever had ~1k at one time in my life so 300k is something I can't even really accurately imagine. I know that I wouldn't have at once obviously, but just to know I would be earning that is kinda crazy to me. I feel like I would be living quite comfortably by the time I'm 30 years old (but risk being too content too soon). I would definitely love to have at least a few years of my 20s to spend with that kind of money before I have a family to spend it all on. I haven't grown up very financially stable so it would be so nice to just spend some money…get a nice car, buy a new guitar or two, eat some good food, and just be financially comfortable. I have always felt like I deserved to make good money in my life, even as a kid growing up, and I just want to have it be a reality. I know that either path I take will make good money by the time I'm ~40-45 years old, but I guess I'm just sick of not making money and am getting impatient about it. However, a big idea pushing me towards a PhD is that I feel the masters path would give me a feeling of selling out if I have the capability to solve real questions in the computer science world. (pretty straight-forward - not much to elaborate on, but this is a big deal) Now onto other aspects of the decision. I originally got into computer science because of programming. I started in high school and knew very soon that it was what I wanted to do for a career. I feel like getting a masters and being a software engineer in the industry gives me much more time to program in my career. In research, I feel like I would spend more time reading, writing, trying to get grant money, etc than I would coding. A guy I work with in the lab just recently published a paper. He showed it to me and I was shocked by it. The first two pages was littered with equations and formulas. Then the next page or so was followed by more equations and formulas that he derived from the previous ones. That was his work - breaking down and creating all of these formulas for robotic arm movement. And whenever I read computer science papers, they all seem to follow this pattern. I always pictured myself coding all day long…not proving equations and things of that nature. I know that's only one part of computer science research, but that part bores me. A couple cons on each side - Phd - I don't really enjoy writing or feel like I'm that great at technical writing. Whenever I'm in groups to make something, I'm always the one who does the large majority of the work and then give it to my team members to write up a report. Presenting is different though - I don't mind presenting at all as long as I have a good grasp on what I am presenting. But writing papers seems like such a chore to me. And because of this, the "publish or perish" phrase really turns me off from research. Another bad thing - I feel like if I am doing research, most of it would be done alone. I work best in small groups. I like to have at least one person to bounce ideas off of when I am brainstorming. The idea of being a part of some small elite group to build things sounds ideal to me. So being able to work in small groups for the majority of my career is a definite plus. I don't feel like I can get this doing research. Masters - I read a lot online that most people come in as engineers and eventually move into management positions. As of now, I don't see myself wanting to be a part of management. Lets say my company wanted to make some new product or system - I would get much more pride, enjoyment, and overall satisfaction to say "I made this" rather than "I managed a group of people that made this." I want to be a big part of the development process. I want to make things. I think it would be great to be more specialized than other people. I would rather know everything about something than something about everything. I always have been that way - was a great pitcher during my baseball years, but not so good at everything else, great at certain classes in school, but not so good at others, etc. To think that my career would be the same way sounds okay to me. Getting a PhD would point me in this direction. It would be great to be some guy who is someone that people look towards and come to ask for help because of being such an important contributor to a very specific field, such as artificial neural networks or robotic haptic perception. From what I gather about the software industry, being specialized can be a very bad thing because of the speed of the new technology. I When it comes to being employed, I have pretty conservative views. I don't want to change companies every 5 years. Maybe this is something everyone wishes, but I would love to just be an important person in one company for 10+ (maybe 20-25+ if I'm lucky!) years if the working conditions were acceptable. I feel like that is more possible as a PhD though, being a professor or researcher. The more I read about people in the software industry, the more it seems like most software engineers bounce from company to company at rapid paces. Some even work like a hired gun from project to project which is NOT what I want AT ALL. But finding a place to make great and important software would be great if that actually happens in the real world. I'm a very competitive person. I thrive on competition. I don't really know why, but I have always been that way even as a kid growing up. Competition always gave me a reason to practice that little extra every night, always push my limits, etc. It seems to me like there is no competition in the research world. It seems like everyone is very relaxed as long as research is being conducted. The only competition is if someone is researching the same thing as you and its whoever can finish and publish first (but everyone seems to careful to check that circumstance). The only noticeable competition to me is just with yourself and your own discipline. I like the idea that in the industry, there is real competition between companies to put out the best product or be put out of business. I feel like this would constantly be pushing me to be better at what I do. One thing that is really pushing me towards a PhD is the lifetime of the things you make. I feel like if you make something truly innovative in the industry…just some really great new application or system…there is a shelf-life of about 5-10 years before someone just does it faster and more efficiently. But with research work, you could create an idea or algorithm that last decades. For instance, the A* search algorithm was described in 1968 and is still widely used today. That is amazing to me. In the words of Palahniuk, "The goal isn't to live forever, its to create something that will." Over anything, I just want to do something that matters. I want my work to help and progress society. Seriously, if I'm stuck programming GUIs for the next 40 years…I might shoot myself in the face. But then again, I hate the idea that less than 1% of the population will come into contact with my work and even less understand its importance. So if anything I have said is false then please inform me. If you think I come off as a masters or PhD, inform me. If you want to give me some extra insight or add on to any point I made, please do. Thank you so much to anyone for any help.

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  • What exactly does the condition in the MIT license imply?

    - by Yannbane
    To quote the license itself: Copyright (C) [year] [copyright holders] Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. I am not exactly sure what the bold part implies. Lets say that I'm creating some library, and I license it under the MIT license. Someone decides to fork that library and to create a closed-source, commercial version. According to the license, he should be free to do that. However, what does he additionally need to do under those terms? Credit me as the creator? I guess the "above copyright notice" refers to the "Copyright (C) [..." part, but, wouldn't that list me as the author of his code (although I technically typed out the code)? And wouldn't including the "permission notice" in what is now his library practically license it under the same conditions that I licensed my own library in? Or, am I interpreting this incorrectly? Does that refer to my obligations to include the copyright and the permission notice?

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  • How to keep background requests in sequence

    - by Jason Lewis
    I'm faced with implementing interfaces for some rather archaic systems, for handling online deposits to stored value accounts (think campus card accounts for students). Here's my dilemma: stage 1 of the process involves passing the user off to a thrid-party site for the credit card transaction, like old-school PayPal. Step two involves using a proprietary protocol for communicating with a legacy system for conducting the actual deposit. Step two requires that each transaction have a unique sequence number, and that the requests' seqnums are in order. Since we're logging each transaction in Postgres, my first thought was to take a number from a sequence in the DB, guaranteeing uniqueness. But since we're dealing with web requests that might come in near-simultaneously, and since latency with the return from the off-ste payment processor is beyond our control, there's always the chance for a race condition in the order of requests passed back to the proprietary system, and if the seqnums are out of order, the request fails silently (brilliant, right?). I thought about enqueuing the requests in Redis and using Resque workers to process them (single worker, single process, so they are processed in order), but we need to be able to give the user feedback as to whether the transaction was processed successfully, so this seems less feasible to me. I've tried to make this application handle concurrency well (as much as possible for a Ruby on Rails app), but now we're in a situation where we have to interact with a system that is designed to be single process, single threaded, and sequential. If it at least gave an "out of order" error, I could just increment (or take the next value off the sequence), but it's designed to fail silently in the event of ANY error. We are handling timeouts in a way that blocks on I/O, but since the application uses multiple workers (Unicorn), that's no guarantee. Any ideas/suggestions would be appreciated.

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  • Building a company and want to know how ethical to put samples from projects I did before on the new company website

    - by Amr ElGarhy
    I built a lot of websites and applications during my life, I can put them under the following categories: Did all the project as a freelancer - For other companies Did part of the project as a freelancer - For other companies Did all the project my self while was working for another company Did the project with team members while was working for another company Did all the project my self and for my self Now I am creating a company with a new brand and have my own employees, My question is: Is it ethical, and normal to put on my new company website, screenshots and info about these projects I created my self before? which to put and which not put from the previous categories?

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  • Is there a secure way to add a database troubleshooting page to an application?

    - by Josh Yeager
    My team makes a product (business management software) that our customers install on their own servers. The product uses a SQL database for data storage and app configuration. There have been quite a few cases where something strange happened in the customer's database (caused by bugs in our app and also sometimes admins who mess with the database). To figure out what is wrong with the data, we have to send SQL scripts to the customer and tell them how to run them on the database server. Then, once we know how to fix it, we have to send another script to repair the data. Is there a secure way to add a page in our application that allows an application admin to enter SQL scripts that read and write directly to the database? Our support team could use that to help customers run these scripts, without needing direct access to the SQL server. My big concerns are that someone might abuse this power to get data they shouldn't have and maybe to erase or modify data that they shouldn't be able to modify. I'm not worried about system admins, because they could find another way to do the same thing. But what if someone else got access to the form? Is there any way to do this kind of thing securely?

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  • Oracle has some very helpful and free code...I think

    - by Casey
    I found that some of the code that Oracle uses is very useful so I don't have to re-invent the wheel. Given this is at the top of the file where the code in question is: /* * Copyright (c) 1997, 2006, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ If I leave the text intact, put it in my C++ header, and credit oracle for each method, and package the source into a static library...is it still a no-no?

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  • Is MVC now the only way to write PHP?

    - by JasonS
    Hey... its XMAS Eve and something is bugging me... yes, I have work on my mind even when I am on holiday. The vast amount of frameworks available for PHP now use MVC. Even ASP.net has its own MVC module. I can see the attraction of MVC, I really can and I use it frequently. The only downside that I can see is that you have to fire up the whole system to execute a page request. Depending on your task this can be a little wasteful. So the question. In a professional environment is this the only way to use PHP nowadays or are their other design methods which have alternative benefits?

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  • Work experience before masters

    - by RJadhav
    I dont know if its the right place to ask such questions: I have a bachelors degree from an Indian university. I want to persue masters in one of the universities in usa, my profile is good enough to get me admitted to the school that I want to get into. I also have an offer letter from one of the top software companies in India (Infosys). I dont know which path to take, I know a masters degree will be of great help in future both in terms of money and career but I do not know whether I want to do it at this moment. I have signed up for both edx and coursera for some of the courses and I really liked learning them online. I am not sure if taking these courses can be a substitute for a masters degree. Also how will i be able to differentiate myself in the real world if I do not have a masters degree, since there are many in india who dont have it. And is it advisable for me to take some work experience say 1-2 years and then apply for a masters degree. Although universities do not explicitly mention work experience as a criteria, will any kind of work experience help me in deciding whether i want to do masters? finally I want to know what are the cons of not doing a masters.

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  • What is the best way to pass data into an API from a website?

    - by Chris Wakoksi
    My main objective is to create a User Interface in order to provision(change the status: activate, deactivate, or suspend) modems. I have received a SOAP developer's guide to the specific type of modem that helps out with the specific values that I need to pass into Iridium's WSDL but I cannot figure out how to do this from a webpage I have created using HTML/CSS, and PHP? I have been told by others that I need to know the portal. I have no idea what that means. I am a beginner programmer who has learned programming for this project. Any suggestions as to how to pass my data into the provisioning API?

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  • Origin of common list-processing function names

    - by Heatsink
    Some higher-order functions for operating on lists or arrays have been repeatedly adopted or reinvented. The functions map, fold[l|r], and filter are found together in several programming languages, such as Scheme, ML, and Python, that don't seem to have a common ancestor. I'm going with these three names to keep the question focused. To show that the names are not universal, here is a sampling of names for equivalent functionality in other languages. C++ has transform instead of map and remove_if instead of filter (reversing the meaning of the predicate). Lisp has mapcar instead of map, remove-if-not instead of filter, and reduce instead of fold (Some modern Lisp variants have map but this appears to be a derived form.) C# uses Select instead of map and Where instead of filter. C#'s names came from SQL via LINQ, and despite the name changes, their functionality was influenced by Haskell, which was itself influenced by ML. The names map, fold, and filter are widespread, but not universal. This suggests that they were borrowed from an influential source into other contemporary languages. Where did these function names come from?

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  • how to generate number pattern in triangular form

    - by Vignesh Vicky
    I want to print this pattern like right angled triangle 0 909 89098 7890987 678909876 56789098765 4567890987654 345678909876543 23456789098765432 1234567890987654321 I wrote following code # include<stdio.h> # include<conio.h> void main() { clrscr(); int i,j,x,z,k,f=1; for ( i=10;i>=1;i--,f++) { for(j=1;j<=f;j++,k--) { k=i; if(k!=10) { printf("%d",k); } if(k==10) { printf("0"); } } for(x=1;x<f;x++,z--) { z=9; printf("%d",z); } printf("%d/n"); } getch(); } what is wrong with this code? when i check manually it seems correct but when compiled gives different pattern

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  • Algorithm to infer tag hierarchy

    - by Tom
    I'm looking for an algorithm to infer a hierarchy from a set of tagged items. E.g. if the following items have the tags: 1 a 2 a,b 3 a,c 4 a,c,e 5 a,b 6 a,c 7 d 8 d,f Then I can construct an undirected graph (or graphs) by tallying the node weights and edge weights: node weights edge weights a 6 a-b 2 b 2 a-c 3 c 3 c-e 1 d 2 a-e 1 <-- this edge is parallel to a-c and c-e and not wanted e 1 d-f 1 f 1 The first problem is how to drop any redundant edges to get to the simplified graph? Note that it's only appropriate to remove that redundant a-e edge in this case because something is tagged as a-c-e, if that wasn't the case and the tag was a-e, that edge would have to remain. I suspect that means the removal of edges can only happen during the construction of the graph, not after everything has been tallied up. What I'd then like to do is identify the direction of the edges to create a directed graph (or graphs) and pick out root nodes to hopefully create a tree (or trees): trees a d // \\ | b c f \ e It seems like it could be a string algorithm - longest common subsequences/prefixes - or a tree/graph algorithm, but I am a little stuck since I don't know the correct terminology to search for it.

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  • Need help identifing what resources (eg. In MIT OpenCourseWare) can help me prepare for a test [closed]

    - by jiewmeng
    I am entering uni soon. I can sit for a placement test to see if I elegible for exemptions. The details are http://www.comp.nus.edu.sg/undergraduates/TestScope11_12.html Or CS2100 Computer Organisation (please click title) The objective of this module is to familiarise students with the fundamentals of computing devices. Through this module students will understand the basics of data representation, and how the various parts of a computer work, separately and with each other. This allows students to understand the issues in computing devices, and how these issues affect the implementation of solutions. Topics covered include data representation systems, combinational and sequential circuit design techniques, assembly language, processor execution cycles, pipelining, memory hierarchy and input/output systems. Recommended Textbooks Digital Design: Principles and Practices [DDPP] by John F. Wakerly, Prentice-Hall. ISBN 0-13-324500-4. Computer Organizations and Design (The hardware/software interface) by David A. Patterson and John L. Hennessy. CS2105 Introduction to Computer Networks (please click title) This course aims to provide a broad introduction to computer networks and some appreciations of network application programming. It covers a range of topics including basic data communication and computer network concepts, protocols, networked computing concepts and principles, network applications development and network security. The emphasis of teaching is on the working principles and application of computer networks. As an integral part of the course, tutorials and practical assignments enforcing learning will also be given. These assignments provide an early exposure in network application programming and they should be able to complete by using personal computers and school's network facilities. Topics included: An overview of computer networks and the Internet Basic data communications Application layer Transport layer Network layer and routing Link layer and local area networks Recommended Textbook James F. Kurose & Keith W. Ross, Computer networking: A top-down approach featuring internet, Addison Wesley, 2001 I am wondering what resources eg. MIT OpenCourseWare or other universities resources are available to help he perpare for these particular modubles. I am thinking does the Networking one look like CCNA? The computer oragization. Its like electronics, assembly etc? I learnt some electronics in Poly but looking at the sample papers, uni looks very different... I have about 1 month to prepare if I want any chance of exempting from these modules :) any help?

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  • What's the equivalent name of "procedure" in OOP?

    - by AeroCross
    In several of my programming courses in the University, my teachers always told me the following: A function and a procedure are basically the same thing: the only difference is that a function returns a value, and the procedure doesn't. That means that this: function sum($a, $b) { return $a + $b; } ... is a function, and this: function sum($a, $b) { echo $a + $b; } ... is a procedure. In the same train of thought, I've seen that a method is the equivalent of a function in the OOP world. That means that this: class Example { function sum($a, $b) { return $a + $b; } } Is a method — but how do you call this? class Example { function sum($a, $b) { echo $a + $b; } } What's the equivalent name, or how do you call a method that doesn't returns anything?

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  • Breaking 1NF to model subset constraints. Does this sound sane?

    - by Chris Travers
    My first question here. Appologize if it is in the wrong forum but this seems pretty conceptual. I am looking at doing something that goes against conventional wisdom and want to get some feedback as to whether this is totally insane or will result in problems, so critique away! I am on PostgreSQL 9.1 but may be moving to 9.2 for this part of this project. To re-iterate: Does it seem sane to break 1NF in this way? I am not looking for debugging code so much as where people see problems that this might lead. The Problem In double entry accounting, financial transactions are journal entries with an arbitrary number of lines. Each line has either a left value (debit) or a right value (credit) which can be modelled as a single value with negatives as debits and positives as credits or vice versa. The sum of all debits and credits must equal zero (so if we go with a single amount field, sum(amount) must equal zero for each financial journal entry). SQL-based databases, pretty much required for this sort of work, have no way to express this sort of constraint natively and so any approach to enforcing it in the database seems rather complex. The Write Model The journal entries are append only. There is a possibility we will add a delete model but it will be subject to a different set of restrictions and so is not applicable here. If and when we allow deletes, we will probably do them using a simple ON DELETE CASCADE designation on the foreign key, and require that deletes go through a dedicated stored procedure which can enforce the other constraints. So inserts and selects have to be accommodated but updates and deletes do not for this task. My Proposed Solution My proposed solution is to break first normal form and model constraints on arrays of tuples, with a trigger that breaks the rows out into another table. CREATE TABLE journal_line ( entry_id bigserial primary key, account_id int not null references account(id), journal_entry_id bigint not null, -- adding references later amount numeric not null ); I would then add "table methods" to extract debits and credits for reporting purposes: CREATE OR REPLACE FUNCTION debits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount < 0 THEN $1.amount * -1 ELSE NULL END; $$; CREATE OR REPLACE FUNCTION credits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount > 0 THEN $1.amount ELSE NULL END; $$; Then the journal entry table (simplified for this example): CREATE TABLE journal_entry ( entry_id bigserial primary key, -- no natural keys :-( journal_id int not null references journal(id), date_posted date not null, reference text not null, description text not null, journal_lines journal_line[] not null ); Then a table method and and check constraints: CREATE OR REPLACE FUNCTION running_total(journal_entry) returns numeric language sql immutable as $$ SELECT sum(amount) FROM unnest($1.journal_lines); $$; ALTER TABLE journal_entry ADD CONSTRAINT CHECK (((journal_entry.running_total) = 0)); ALTER TABLE journal_line ADD FOREIGN KEY journal_entry_id REFERENCES journal_entry(entry_id); And finally we'd have a breakout trigger: CREATE OR REPLACE FUNCTION je_breakout() RETURNS TRIGGER LANGUAGE PLPGSQL AS $$ BEGIN IF TG_OP = 'INSERT' THEN INSERT INTO journal_line (journal_entry_id, account_id, amount) SELECT NEW.id, account_id, amount FROM unnest(NEW.journal_lines); RETURN NEW; ELSE RAISE EXCEPTION 'Operation Not Allowed'; END IF; END; $$; And finally CREATE TRIGGER AFTER INSERT OR UPDATE OR DELETE ON journal_entry FOR EACH ROW EXECUTE_PROCEDURE je_breaout(); Of course the example above is simplified. There will be a status table that will track approval status allowing for separation of duties, etc. However the goal here is to prevent unbalanced transactions. Any feedback? Does this sound entirely insane? Standard Solutions? In getting to this point I have to say I have looked at four different current ERP solutions to this problems: Represent every line item as a debit and a credit against different accounts. Use of foreign keys against the line item table to enforce an eventual running total of 0 Use of constraint triggers in PostgreSQL Forcing all validation here solely through the app logic. My concerns are that #1 is pretty limiting and very hard to audit internally. It's not programmer transparent and so it strikes me as being difficult to work with in the future. The second strikes me as being very complex and required a series of contraints and foreign keys against self to make work, and therefore it strikes me as complex, hard to sort out at least in my mind, and thus hard to work with. The fourth could be done as we force all access through stored procedures anyway and this is the most common solution (have the app total things up and throw an error otherwise). However, I think proof that a constraint is followed is superior to test cases, and so the question becomes whether this in fact generates insert anomilies rather than solving them. If this is a solved problem it isn't the case that everyone agrees on the solution....

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  • How do we know to favour composition over generalisation is always the right choice?

    - by Carnotaurus
    Whether an object physically exists or not, we can choose to model it in different ways. We could arbitarily use generalisation or composition in many cases. However, the GoF principle of "favour composition over generalisation [sic]" guides us to use composition. So, when we model, for example, a line then we create a class that contains two members PointA and PointB of the type Point (composition) instead of extending Point (generalisation). This is just a simplified example of how we can arbitarily choose composition or inheritance to model, despite that objects are usually much more complex. How do we know that this is the right choice? It matters at least because there could be a ton of refactoring to do if it is wrong?

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  • What features would you like to have in PHP? [closed]

    - by StasM
    Since it's the holiday season now and everybody's making wishes, I wonder - which language features you would wish PHP would have added? I am interested in some practical suggestions/wishes for the language. By practical I mean: Something that can be practically done (not: "I wish PHP would guess what my code means and fix bugs for me" or "I wish any code would execute under 5ms") Something that doesn't require changing PHP into another language (not: "I wish they'd drop $ signs and use space instead of braces" or "I wish PHP were compiled, statically typed and had # in it's name") Something that would not require breaking all the existing code (not: "Let's rename 500 functions and change parameter order for them") Something that does change the language or some interesting aspect of it (not: "I wish there was extension to support for XYZ protocol" or "I wish bug #12345 were finally fixed") Something that is more than a rant (not: "I wish PHP wouldn't suck so badly") Anybody has any good wishes? Mod edit: Stanislav Malyshev is a core PHP developer.

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  • SQL Error: ORA-00936: missing expression

    - by user2901548
    Qns: Item Description and the treatment date of all treatments for any patients named Jessie Stange (ie GivenName is Jessie & FamilyName is Stange) What i wrote: SELECT DISTINCT Description, Date as treatmentDate WHERE doothey.Patient P, doothey.Account A, doothey.AccountLine AL, doothey.Item.I AND P.PatientID = A.PatientID AND A.AccountNo = AL.AccountNo AND AL.ItemNo = I.ItemNo AND (p.FamilyName = 'Stange' AND p.GivenName = 'Jessie'); error: Error at Command Line:1 Column:30 Error report: SQL Error: ORA-00936: missing expression 00936. 00000 - "missing expression" *Cause: *Action: What is the missing expression???

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  • Why does a proportional controller have a steady state error?

    - by Qantas 94 Heavy
    I've read about feedback loops, how much this steady state error is for a given gain and what to do to remove this steady state error (add integral and/or derivative gains to the controller), but I don't understand at all why this steady state error occurs in the first place. If I understand how a proportional control works correctly, the output is equal to the current output plus the error, multiplied by the proportional gain (Kp). However, wouldn't the error slowly diminish over time as it is added (reaching 0 at infinite time), not have a steady state error? From my confusion, it seems I'm completely misunderstanding how it works - a proper explanation of how this steady state error eventuates would be fantastic.

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  • methods DSA_do_verify and SHA1 (OpenSSL library for Windows)

    - by Rei
    i am working on a program to authenticate an ENC signature file by using OpenSSL for windows, and specifically methods DSA_do_verify(...) and SHA1(...) hash algorithm, but is having problems as the result from DSA_do_verify is always 0 (invalid). I am using the signature file of test set 4B from the IHO S-63 Data Protection Scheme, and also the SA public key (downloadable from IHO) for verification. Below is my program, can anyone help to see where i have gone wrong as i have tried many ways but failed to get the verification to be valid, thanks.. The signature file from test set 4B // Signature part R: 3F14 52CD AEC5 05B6 241A 02C7 614A D149 E7D6 C408. // Signature part S: 44BB A3DB 8C46 8D11 B6DB 23BE 1A79 55E6 B083 7429. // Signature part R: 93F5 EF86 1FF6 BA6F 1C2B B9BB 7F36 0C80 2F9B 2414. // Signature part S: 4877 8130 12B4 50D8 3688 B52C 7A84 8E26 D442 8B6E. // BIG p C16C BAD3 4D47 5EC5 3966 95D6 94BC 8BC4 7E59 8E23 B5A9 D7C5 CEC8 2D65 B682 7D44 E953 7848 4730 C0BF F1F4 CB56 F47C 6E51 054B E892 00F3 0D43 DC4F EF96 24D4 665B. // BIG q B7B8 10B5 8C09 34F6 4287 8F36 0B96 D7CC 26B5 3E4D. // BIG g 4C53 C726 BDBF BBA6 549D 7E73 1939 C6C9 3A86 9A27 C5DB 17BA 3CAC 589D 7B3E 003F A735 F290 CFD0 7A3E F10F 3515 5F1A 2EF7 0335 AF7B 6A52 11A1 1035 18FB A44E 9718. // BIG y 15F8 A502 11C2 34BB DF19 B3CD 25D1 4413 F03D CF38 6FFC 7357 BCEE 59E4 EBFD B641 6726 5E5F 0682 47D4 B50B 3B86 7A85 FB4D 6E01 8329 A993 C36C FD9A BFB6 ED6D 29E0. dataServer_pkeyfile.txt (extracted from above) // BIG p C16C BAD3 4D47 5EC5 3966 95D6 94BC 8BC4 7E59 8E23 B5A9 D7C5 CEC8 2D65 B682 7D44 E953 7848 4730 C0BF F1F4 CB56 F47C 6E51 054B E892 00F3 0D43 DC4F EF96 24D4 665B. // BIG q B7B8 10B5 8C09 34F6 4287 8F36 0B96 D7CC 26B5 3E4D. // BIG g 4C53 C726 BDBF BBA6 549D 7E73 1939 C6C9 3A86 9A27 C5DB 17BA 3CAC 589D 7B3E 003F A735 F290 CFD0 7A3E F10F 3515 5F1A 2EF7 0335 AF7B 6A52 11A1 1035 18FB A44E 9718. // BIG y 15F8 A502 11C2 34BB DF19 B3CD 25D1 4413 F03D CF38 6FFC 7357 BCEE 59E4 EBFD B641 6726 5E5F 0682 47D4 B50B 3B86 7A85 FB4D 6E01 8329 A993 C36C FD9A BFB6 ED6D 29E0. Program abstract: QbyteArray pk_data; QFile pk_file("./dataServer_pkeyfile.txt"); if (pk_file.open(QIODevice::Text | QIODevice::ReadOnly)) { pk_data.append(pk_file.readAll()); } pk_file.close(); unsigned char ptr_sha_hashed[20]; unsigned char *ptr_pk_data = (unsigned char *)pk_data.data(); // openssl SHA1 hashing algorithm SHA1(ptr_pk_data, pk_data.length(), ptr_sha_hashed); DSA_SIG *dsasig = DSA_SIG_new(); char ptr_r[] = "93F5EF861FF6BA6F1C2BB9BB7F360C802F9B2414"; //from tset 4B char ptr_s[] = "4877813012B450D83688B52C7A848E26D4428B6E"; //from tset 4B if (BN_hex2bn(&dsasig->r, ptr_r) == 0) return 0; if (BN_hex2bn(&dsasig->s, ptr_s) == 0) return 0; DSA *dsakeys = DSA_new(); //the following values are from the SA public key char ptr_p[] = "FCA682CE8E12CABA26EFCCF7110E526DB078B05EDECBCD1EB4A208F3AE1617AE01F35B91A47E6DF63413C5E12ED0899BCD132ACD50D99151BDC43EE737592E17"; char ptr_q[] = "962EDDCC369CBA8EBB260EE6B6A126D9346E38C5"; char ptr_g[] = "678471B27A9CF44EE91A49C5147DB1A9AAF244F05A434D6486931D2D14271B9E35030B71FD73DA179069B32E2935630E1C2062354D0DA20A6C416E50BE794CA4"; char ptr_y[] = "963F14E32BA5372928F24F15B0730C49D31B28E5C7641002564DB95995B15CF8800ED54E354867B82BB9597B158269E079F0C4F4926B17761CC89EB77C9B7EF8"; if (BN_hex2bn(&dsakeys->p, ptr_p) == 0) return 0; if (BN_hex2bn(&dsakeys->q, ptr_q) == 0) return 0; if (BN_hex2bn(&dsakeys->g, ptr_g) == 0) return 0; if (BN_hex2bn(&dsakeys->pub_key, ptr_y) == 0) return 0; int result; //valid = 1, invalid = 0, error = -1 result = DSA_do_verify(ptr_sha_hashed, 20, dsasig, dsakeys); //result is 0 (invalid)

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