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  • Learning how to design knowledge and data flow [closed]

    - by max
    In designing software, I spend a lot of time deciding how the knowledge (algorithms / business logic) and data should be allocated between different entities; that is, which object should know what. I am asking for advice about books, articles, presentations, classes, or other resources that would help me learn how to do it better. I code primarily in Python, but my question is not really language-specific; even if some of the insights I learn don't work in Python, that's fine. I'll give a couple examples to clarify what I mean. Example 1 I want to perform some computation. As a user, I will need to provide parameters to do the computation. I can have all those parameters sent to the "main" object, which then uses them to create other objects as needed. Or I can create one "main" object, as well as several additional objects; the additional objects would then be sent to the "main" object as parameters. What factors should I consider to make this choice? Example 2 Let's say I have a few objects of type A that can perform a certain computation. The main computation often involves using an object of type B that performs some interim computation. I can either "teach" A instances what exact parameters to pass to B instances (i.e., make B "dumb"); or I can "teach" B instances to figure out what needs to be done when looking at an A instance (i.e., make B "smart"). What should I think about when I'm making this choice?

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  • High-Level Application Architecture Question

    - by Jesse Bunch
    So I'm really wanting to improve how I architect the software I code. I want to focus on maintainability and clean code. As you might guess, I've been reading a lot of resources on this topic and all it's doing is making it harder for me to settle on an architecture because I can never tell if my design is the one that the more experienced programmer would've chosen. So I have these requirements: I should connect to one vendor and download form submissions from their API. We'll call them the CompanyA. I should then map those submissions to a schema fit for submitting to another vendor for integration with the email service provider. We'll call them the CompanyB. I should then submit those responses to the ESP (CompanyB) and then instruct the ESP to send that submitter an email. So basically, I'm copying data from one web service to another and then performing an action at the latter web service. I've identified a couple high-level services: The service that downloads data from CompanyA. I called this the CompanyAIntegrator. The service that submits the data to CompanyB. I called this CompanyBIntegrator. So my questions are these: Is this a good design? I've tried to separate the concerns and am planning to use the facade pattern to make the integrators interchangeable if the vendors change in the future. Are my naming conventions accurate and meaningful to you (who knows nothing specific of the project)? Now that I have these services, where should I do the work of taking output from the CompanyAIntegrator and getting it in the format for input to the CompanyBIntegrator? Is this OK to be done in main()? Do you have any general pointers on how you'd code something like this? I imagine this scenario is common to us engineers---especially those working in agencies. Thanks for any help you can give. Learning how to architect well is really mind-cluttering.

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  • How bad is it to have two methods with the same name but different signatures in two classes?

    - by Super User
    I have a design problem related to a public interface, the names of methods, and the understanding of my API and code. I have two classes like this: class A: ... function collision(self): .... ... class B: .... function _collision(self, another_object, l, r, t, b): .... The first class has one public method named collision, and the second has one private method called _collision. The two methods differs in argument type and number. As an example let's say that _collision checks if the object is colliding with another object with certain conditions l, r, t, b (collide on the left side, right side, etc) and returns true or false. The public collision method, on the other hand, resolves all the collisions of the object with other objects. The two methods have the same name because I think it's better to avoid overloading the design with different names for methods that do almost the same thing, but in distinct contexts and classes. Is this clear enough to the reader or I should change the method's name?

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  • How bad it's have two methods with the same name but differents signatures in two classes?

    - by Super User
    I have a design problem relationated with the public interface, the names of methods and the understanding of my API and my code. I have two classes like this: class A: ... function collision(self): .... ... class B: .... function _collision(self, another_object, l, r, t, b): .... The first class have one public method named collision and the second have one private method called _collision. The two methods differs in arguments type and number. In the API _m method is private. For the example let's say that the _collision method checks if the object is colliding with another_ object with certain conditions l, r, t, b (for example, collide the left side, the right side, etc) and returns true or false according to the case. The collision method, on the other hand, resolves all the collisions of the object with other objects. The two methods have the same name because I think is better avoid overload the design with different names for methods who do almost the same think, but in distinct contexts and classes. This is clear enough to the reader or I should change the method's name?

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  • Templates for forms, tabs etc? - Patterntap alternatives

    - by Marco Demaio
    I used to find http://www.patterntap.com quite useful to get design inspiration for forms, tabs, and other web elements etc. Unfortunately after the ZURB acquisition of Patterntap now they enforce you to sign in with your Twitter account in order to simply view larger images of patterns provided by the crowd. So in some way it's not free anymore. Do you know of alternatives to patterntap that are free and you are not obliged to sign in?

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  • Representing complex object dependencies

    - by max
    I have several classes with a reasonably complex (but acyclic) dependency graph. All the dependencies are of the form: class X instance contains an attribute of class Y. All such attributes are set during initialization and never changed again. Each class' constructor has just a couple parameters, and each object knows the proper parameters to pass to the constructors of the objects it contains. class Outer is at the top of the dependency hierarchy, i.e., no class depends on it. Currently, the UI layer only creates an Outer instance; the parameters for Outer constructor are derived from the user input. Of course, Outer in the process of initialization, creates the objects it needs, which in turn create the objects they need, and so on. The new development is that the a user who knows the dependency graph may want to reach deep into it, and set the values of some of the arguments passed to constructors of the inner classes (essentially overriding the values used currently). How should I change the design to support this? I could keep the current approach where all the inner classes are created by the classes that need them. In this case, the information about "user overrides" would need to be passed to Outer class' constructor in some complex user_overrides structure. Perhaps user_overrides could be the full logical representation of the dependency graph, with the overrides attached to the appropriate edges. Outer class would pass user_overrides to every object it creates, and they would do the same. Each object, before initializing lower level objects, will find its location in that graph and check if the user requested an override to any of the constructor arguments. Alternatively, I could rewrite all the objects' constructors to take as parameters the full objects they require. Thus, the creation of all the inner objects would be moved outside the whole hierarchy, into a new controller layer that lies between Outer and UI layer. The controller layer would essentially traverse the dependency graph from the bottom, creating all the objects as it goes. The controller layer would have to ask the higher-level objects for parameter values for the lower-level objects whenever the relevant parameter isn't provided by the user. Neither approach looks terribly simple. Is there any other approach? Has this problem come up enough in the past to have a pattern that I can read about? I'm using Python, but I don't think it matters much at the design level.

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  • In database table design, how does "Virtual Goods" affect table design -- should we create an instan

    - by Jian Lin
    When we design a database table for a DVD rental company, we actually have a movie, which is an abstract idea, and a physical DVD, so for each rental, we have a many-to-many table with fields such as: TransactionID UserID DvdID RentedDate RentalDuration AmountPaid but what about with virtual goods? For example, if we let a user rent a movie online for 3 days, we don't actually have a DVD, so we may have a table: TransactionID UserID MovieID RentedDate RentalDuration AmountPaid should we create a record for each instance of "virtual good"? For example, what if this virtual good (the movie) can be authorized to be watched on 3 devices (with 3 device IDs), then should we then create a virtual good record in the VirtualGoods table, each with a VirtualGoodID and then another table that has VirtualGoodID DeviceID to match up the movie with the DeviceIDs? We can also just use the TransactionID as the VirtualGoodID. Are there circumstances where we may want to create a record to record this "virtual good" in a VirtualGoods table?

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  • Creating a dummy design before the development starts

    - by NLV
    Hello How can i create a dummy design of an application before the actual development starts? How to simulate the UI of the application. After completing the analysis phase do i need to start the design directly using dev tools or can i create some dummies (even images, using Visio or something) with other tools? Thank you

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  • What do you do if you reach a design dead-end in evolutionary methods like Agile or XP?

    - by Dipan Mehta
    As I was reading Martin Fowler's famous blog post Is Design Dead?, one of the striking impressions I got is that given the fact that in Agile Methodology and Extreme Programming, the design as well as programming is evolutionary, there are always points where things need to get refactored. It may be possible that when a programmer's level is good, and they understand design implications and don't make critical mistakes, the code continues to evolve. However, in a normal context, what is the ground reality in this context? In a normal day given some significant development goes into product, and when critical change occurs in requirement isn't it a constraint that how much ever we wish, fundamental design aspects cannot be modified? (without throwing away major part of the code). Is it not quite likely that one reaches dead-end on any further possible improvement on design and requirements? I am not advocating any non-Agile practice here, but I want to know from people who practice agile or iterative or evolutionary development methods, as for their real experiences. Have you ever reached such dead-ends? How have you managed to avoid it or escaped it? Or are there measures to ensure that design remains clean and flexible as it evolves?

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  • Object oriented wrapper around a dll

    - by Tom Davies
    So, I'm writing a C# managed wrapper around a native dll. The dll contains several hundred functions. In most cases, the first argument to each function is an opaque handle to a type internal to the dll. So, an obvious starting point for defining some classes in the wrapper would be to define classes corresponding to each of these opaque types, with each instance holding and managing the opaque handle (passed to its constructor) Things are a little awkward when dealing with callbacks from the dll. Naturally, the callback handlers in my wrapper have to be static, but the callbacks arguments invariable contain an opaque handle. In order to get from the static callback back to an object instance, I've created a static dictionary in each class, associating handles with class instances. In the constructor of each class, an entry is put into the dictionary, and this entry is then removed in the Destructors. When I receive a callback, I can then consult the dictionary to retrieve the class instance corresponding to the opaque reference. Are there any obvious flaws to this? Something that seems to be a problem is that the existence static dictionary means that the garbage collector will not act on my class instances that are otherwise unreachable. As they are never garbage collected, they never get removed from the dictionary, so the dictionary grows. It seems I might have to manually dispose of my objects, which is something absolutely would like to avoid. Can anyone suggest a good design that allows me to avoid having to do this?

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  • Process for beginning a Ruby on Rails project

    - by Daniel Beardsley
    I'm about to begin a Ruby on Rails project and I'd love to hear how others go through the process of starting an application design. I have quite a bit of experience with RoR, but don't have that many starting from scratch with only a vision experiences and would appreciate the wisdom of others who've been there. I'm looking for an order of events, reasons for the order, and maybe why each part is important. I can think of a few starting points, but I'm not sure where it's best to begin Model design and relationships (entities, how they relate, and their attributes) Think of user use-cases (or story-boards) and implement the minimum to get these done Create Model unit-tests then create the necessary migrations and AR models to get the tests to pass Hack out the most basic version of the simplest part of your application and go from there Start with a template for a rails app (like http://github.com/thoughtbot/suspenders) Do the boring gruntwork first (User auth, session management, ...) ...

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  • How should I remember what I was doing and why on a project 3 months back?

    - by TheIndependentAquarius
    I was working on this project 3 months back, and then suddenly another urgent project appeared and I was asked to shift my attention there. Now, from tomorrow I'll be heading back to my old project and I realize that I do not remember what exactly was I doing and where to start! I wish to know how to document the project such that anytime I look back it shouldn't take me more than a few minutes to get going from wherever I left!

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  • How do we keep dependent data structures up to date?

    - by Geo
    Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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  • Way to update / refresh / reschedule project plan after adding a vacation / changing calendar

    - by CodeCanvas
    I had created a project plan using MS-Project 2010 (not server). I had set the task schedule mode to "Auto Scheduled" and entered the necessary tasks. Since it is a single person project I also added one person to the Resource of the file and assigned that resource to all the tasks and leveled the project. After the plan was put in and tasks were leveled I figured the calendar was not correctly set (in UAE the weekend is Friday and Saturday instead of Saturday and Sunday). So, I updated the default calendar (Standard) of the project by going to Project-Change Working Time-Work Weeks and changed them as needed. But after doing this, the tasks are still scheduled over Friday and Saturday even though I have marked them as nonworking days in the standard calendar. I tried the following for the tasks to refresh, but I was not successful: Updated all tasks to use the "Standard" calendar in the project Selected option so that tasks do not ignore resource calendars Added a constraint "As Soon As Possible" Executed "Level All" Any help on solving this issue would be much appreciated, thanks in advance.

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  • FilePageSetupHeader in MS Project VBA project: Display image dynamically

    - by Anne Schuessler
    I want to display an image when printing a page from MS Page using the FilePageSetupHeader. It all works fine if I pass in the parameter for the Text property as a string as such FilePageSetupHeader Alignment:=pjRight, Text:="&P""C:\filepath\image.gif""" However, I'd prefer to be able to pass the filepath to the image to display as a variable. Somehow I can't get it right. So if I try something like the following: vImagePath = """&P""""" & prjFilePath & "\image.gif"""""" FilePageSetupHeader Alignment:=pjRight, Text:=vImagePath it just displays the path as a string. I'm pretty sure it boils down to something simple like escaping the quotes in the correct way, but I've been playing around with it for a while now and I can't seem to get it right. Any idea how this works?

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  • PERT shows relationships between defined tasks in a project without taking into consideration a time line

    The program evaluation and review technique (PERT) shows relationships between defined tasks in a project without taking into consideration a time line. This chart is an excellent way to identify dependencies of tasks based on other tasks. This chart allows project managers to identify the critical path of a project to minimize any time delays to the project. According to Craig Borysowich in his article “Pros & Cons of the PERT/CPM Method stated the following advantages and disadvantages: “PERT/CPM has the following advantages: A PERT/CPM chart explicitly defines and makes visible dependencies (precedence relationships) between the WBS elements, PERT/CPM facilitates identification of the critical path and makes this visible, PERT/CPM facilitates identification of early start, late start, and slack for each activity, PERT/CPM provides for potentially reduced project duration due to better understanding of dependencies leading to improved overlapping of activities and tasks where feasible.  PERT/CPM has the following disadvantages: There can be potentially hundreds or thousands of activities and individual dependency relationships, The network charts tend to be large and unwieldy requiring several pages to print and requiring special size paper, The lack of a timeframe on most PERT/CPM charts makes it harder to show status although colors can help (e.g., specific color for completed nodes), When the PERT/CPM charts become unwieldy, they are no longer used to manage the project.” (Borysowich, 2008) Traditionally PERT charts are used in the initial planning of a project like in a project that is utilizing the waterfall approach. Once the chart was created then project managers could further analyze this data to determine the earliest start time for each stage in the project. This is important because this information can be used to help forecast resource needs during a project and where in the project. However, the agile environment can approach this differently because of their constant need to be in contact with the client and the other stakeholders.  The PERT chart can also be used during project iteration to determine what is to be worked on next, such as a prioritized To-Do list a wife would give her husband at the start of a weekend. In my personal opinion, the COTS-centric environment would not really change how a company uses a PERT chart in their day to day work. The only thing I can is that there would be less tasks to include in the chart because the functionally milestones are already completed when the components are purchased. References: http://www.netmba.com/operations/project/pert/ http://web2.concordia.ca/Quality/tools/20pertchart.pdf http://it.toolbox.com/blogs/enterprise-solutions/pros-cons-of-the-pertcpm-method-22221

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  • Common business drivers that lead to creating and sustaining a project

    Common business drivers that lead to creating and sustaining a project include and are not limited to: cost reduction, increased return on investment (ROI), reduced time to market, increased speed and efficiency, increased security, and increased interoperability. These drivers primarily focus on streamlining and reducing cost to make a company more profitable with less overhead. According to Answers.com cost reduction is defined as reducing costs to improve profitability, and may be implemented when a company is having financial problems or prevent problems. ROI is defined as the amount of value received relative to the amount of money invested according to PayperclickList.com.  With the ever increasing demands on businesses to compete in today’s market, companies are constantly striving to reduce the time it takes for a concept to become a product and be sold within the global marketplace. In business, some people say time is money, so if a project can reduce the time a business process takes it in fact saves the company which is always good for the bottom line. The Social Security Administration states that data security is the protection of data from accidental or intentional but unauthorized modification, destruction. Interoperability is the capability of a system or subsystem to interact with other systems or subsystems. In my personal opinion, these drivers would not really differ for a profit-based organization, compared to a non-profit organization. Both corporate entities strive to reduce cost, and strive to keep operation budgets low. However, the reasoning behind why they want to achieve this does contrast. Typically profit based organizations strive to increase revenue and market share so that the business can grow. Alternatively, not-for-profit businesses are more interested in increasing their reach within communities whether it is to increase annual donations or invest in the lives of others. Success or failure of a project can be determined by one or more of these drivers based on the scope of a project and the company’s priorities associated with each of the drivers. In addition, if a project attempts to incorporate multiple drivers and is only partially successful, then the project might still be considered to be a success due to how close the project was to meeting each of the priorities. Continuous evaluation of the project could lead to a decision to abort a project, because it is expected to fail before completion. Evaluations should be executed after the completion of every software development process stage. Pfleeger notes that software development process stages include: Requirements Analysis and Definition System Design Program Design Program Implementation Unit Testing Integration Testing System Delivery Maintenance Each evaluation at every state should consider all the business drivers included in the scope of a project for how close they are expected to meet expectations. In addition, minimum requirements of acceptance should also be included with the scope of the project and should be reevaluated as the project progresses to ensure that the project makes good economic sense to continue. If the project falls below these benchmarks then the project should be put on hold until it does make more sense or the project should be aborted because it does not meet the business driver requirements.   References Cost Reduction Program. (n.d.). Dictionary of Accounting Terms. Retrieved July 19, 2009, from Answers.com Web site: http://www.answers.com/topic/cost-reduction-program Government Information Exchange. (n.d.). Government Information Exchange Glossary. Retrieved July 19, 2009, from SSA.gov Web site: http://www.ssa.gov/gix/definitions.html PayPerClickList.com. (n.d.). Glossary Term R - Pay Per Click List. Retrieved July 19, 2009, from PayPerClickList.com Web site: http://www.payperclicklist.com/glossary/termr.html Pfleeger, S & Atlee, J.(2009). Software Engineering: Theory and Practice. Boston:Prentice Hall Veluchamy, Thiyagarajan. (n.d.). Glossary « Thiyagarajan Veluchamy’s Blog. Retrieved July 19, 2009, from Thiyagarajan.WordPress.com Web site: http://thiyagarajan.wordpress.com/glossary/

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  • How to avoid having very large objects with Domain Driven Design

    - by Pablojim
    We are following Domain Driven Design for the implementation of a large website. However by putting the behaviour on the domain objects we are ending up with some very large classes. For example on our WebsiteUser object, we have many many methods - e.g. dealing with passwords, order history, refunds, customer segmentation. All of these methods are directly related to the user. Many of these methods delegate internally to other child object but this still results in some very large classes. I'm keen to avoid exposing lots of child objects e.g. user.getOrderHistory().getLatestOrder(). What other strategies can be used to avoid this problems?

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  • Solutions for Project management [closed]

    - by user14416
    The team consists of 3 people. The method of development is Scrum. The language of the project is C++. The project will be under the control of the git system. The start up budget is 0. The following things have to be chosen: Build and Version Numbering Project documentation ( file with the most common info for current stage of the project, which will be changed every time the new version or subversion of the project emerges ) Project management tool ( like Trac or Redmine, I cannot use them, because there is no hosting ) Code documentation ( I consider Doxygen ) The following questions have arisen: What can you add to the above list of the main solutions for project management in the described project? One of three project participants has linux os (No MS Office), one has Windows and MS Office (does not want to use Libre or Open Office), one has Windows, but does not have MS Office. What formats, tools can u suggest using for project documentation? The variant of using online wiki does not fit, it must be files. OneNote mb is a good tool for project management, but because of the reason mentioned above it is not possible. What can you advise? Offer a system for Build and Version Numbering.

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  • Subclassing to avoid line length

    - by Super User
    The standard line length of code is 80 characters per line. This is accepted and followed by the most of programmers. I working on a state machine of a character and is necessary for me follow this too. I have four classes who pass this limit. I can subclass each class in two more and then avoid the line length limit. class Stand class Walk class Punch class Crouch The new classes would be StandLeft, StandRight and so on. Stand, Walk, Punch and Crouch would be then abstract classes. The question if there is a limit for the long of the hierarchies tree or this is depends of the case.

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  • Why should ViewModel route actions to Controller when using the MVCVM pattern?

    - by Lea Hayes
    When reading examples across the Internet (including the MSDN reference) I have found that code examples are all doing the following type of thing: public class FooViewModel : BaseViewModel { public FooViewModel(FooController controller) { Controller = controller; } protected FooController Controller { get; private set; } public void PerformSuperAction() { // This just routes action to controller... Controller.SuperAction(); } ... } and then for the view: public class FooView : BaseView { ... private void OnSuperButtonClicked() { ViewModel.PerformSuperAction(); } } Why do we not just do the following? public class FooView : BaseView { ... private void OnSuperButtonClicked() { ViewModel.Controller.SuperAction(); // or, even just use a shortcut property: Controller.SuperAction(); } }

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  • How do I handle priority and propagation in an event system?

    - by Peeter
    Lets say I have a simple event system with the following syntax: object = new Object(); object.bind("my_trigger", function() { print "hello"; }); object.bind("my_trigger", function() { print "hello2"; }); object.trigger("my_trigger"); How could I make sure hello2 is printed out first (I do not want my code to depend on which order the events are binded). Ontop of that, how would I prevent my events from propagating (e.g. I want to stop every other event from being executed)

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  • DDD: service contains two repository

    - by tikhop
    Does it correct way to have two repository inside one service and will it be an application or domain service? Suppose I have a Passenger object that should contains Passport (government id) object. I am getting Passenger from PassengerRepository. PassengerRepository create request to server and obtain data (json) than parse received data and store inside repository. I have confused because I want to store Passport as Entity and put it to PassportRepository but all information about password contains inside json than i received above. I guess that I should create a PassengerService that will be include PassengerRepository and PassportRepository with several methods like removePassport, addPassport, getAllPassenger and etc. UPDATE: So I guess that the better way is represent Passport as VO and store all passports inside Passenger aggregate. However there is another question: Where I should put the methods (methods calls server api) for management passenger's passport. I think the better place is so within Passenger aggregate.

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  • Project Server 2010 Beta - can't connect Project client to projects hosted on server

    - by Chris W
    We have a Project 2010 Beta installed on SharePoint 2010 Beta as test set-up whilst we wait for the release versions. Whilst the installation seemed to complete without any issues we're unable to open any projects within the Project 2010 client app. Project pops up an error 'Could not retrieve server initialization data'. My local event logs list some errors from MSSOAP that simply state an unanticipated error occurred during the processing of the request. The server doesn't log any errors. The Sharepoint set up is a farm containing 3 SharePoint servers. I log in to server 'PORTAL' but the Project Server stuff is configured to run on one of the other SharePoint boxes. I presume others have managed to get this working - has anyone got any ideas as to what could be wrong. Everything is patched correctly as far as I can tell.

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