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  • In an Entity/Component system, can component data be implemented as a simple array of key-value pairs? [on hold]

    - by 010110110101
    I'm trying to wrap my head around how to organize components in an Entity Component Systems once everything in the current scene/level is loaded in memory. (I'm a hobbyist BTW) Some people seem to implement the Entity as an object that contains a list of of "Component" objects. Components contain data organized as an array of key-value pairs. Where the value is serialized "somehow". (pseudocode is loosely in C# for brevity) class Entity { Guid _id; List<Component> _components; } class Component { List<ComponentAttributeValue> _attributes; } class ComponentAttributeValue { string AttributeName; object AttributeValue; } Others describe Components as an in-memory "table". An entity acquires the component by having its key placed in a table. The attributes of the component-entity instance are like the columns in a table class Renderable_Component { List<RenderableComponentAttributeValue> _entities; } class RenderableComponentAttributeValue { Guid entityId; matrix4 transformation; // other stuff for rendering // everything is strongly typed } Others describe this actually as a table. (and such tables sound like an EAV database schema BTW) (and the value is serialized "somehow") Render_Component_Table ---------------- Entity Id Attribute Name Attribute Value and when brought into running code: class Entity { Guid _id; Dictionary<string, object> _attributes; } My specific question is: Given various components, (Renderable, Positionable, Explodeable, Hideable, etc) and given that each component has an attribute with a particular name, (TRANSLATION_MATRIX, PARTICLE_EMISSION_VELOCITY, CAN_HIDE, FAVORITE_COLOR, etc) should: an entity contain a list of components where each component, in turn, has their own array of named attributes with values serialized somehow or should components exist as in-memory tables of entity references and associated with each "row" there are "columns" representing the attribute with values that are specific to each entity instance and are strongly typed or all attributes be stored in an entity as a singular array of named attributes with values serialized somehow (could have name collisions) or something else???

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  • how to improve design ability

    - by Cong Hui
    I recently went on a couple of interviews and all of them asked a one or two design questions, like how you would design a chess, monopoly, and so on. I didn't do good on those since I am a college student and lack of the experience of implementing big and complex systems. I figure the only way to improve my design capability is to read lots of others' code and try to implement myself. Therefore, for those companies that ask these questions, what are their real goals in this? I figure most of college grads start off working in a team guided by a senior leader in their first jobs. They might not have lots of design experience fresh out of colleges. Anyone could give pointers about how to practice those skills? Thank you very much

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  • How To Deal With Terrible Design Decisions

    - by splatto
    I'm a consultant at one company. There is another consultant who is a year older than me and has been here 3 months longer than I have, and a full time developer. The full-time developer is great. My concern is that I see the consultant making absolutely terrible design decisions. For example, M:M relationships are being stored in the database as a comma-delimited string rather than using a conjunction table to hold the relationships. For example, consider two tables, Car and Property: Car records: Camry Volvo Mercedes Property records: Spare Tire Satellite Radio Ipod Support Standard Rather than making a table CarProperties to represent this, he has made a "Property" attribute on the Car table whose data looks like "1,3,7,13,19,25," I hate how this decision and others are affecting the quality of my code. We have butted heads over this design three times in the past two months since I've been here. He asked me why my suggestion was better, and I responded that our database would be eliminating redundant data by converting to a higher normal form. I explained that this design flaw in particular is discussed and discouraged in entry level college programs, and he responded with a shot at me saying that these comma-separated-value database properties are taught when you do your masters (which neither of us have). Needless to say, he became very upset and demanded I apologize for criticizing his work, which I did in the interest of not wanting to be the consultant to create office drama. Our project manager is focused on delivering a product ASAP and is a very strong personality - Suggesting to him at this point that we spend some time to do this right will set him off. There is a strong likelihood that both of our contracts will be extended to work on a second project coming up. How will I be able to exert dominant influence over the design of the system and the data model to ensure that such terrible mistakes are not repeated in the next project? A glimpse at the dynamics: I can be a strong personality if I don't measure myself. The other consultant is not a strong personality, is a poor communicator, is quite stubborn and thinks he is better than everyone else. The project manager is an extremely strong personality who is focused on releasing tomorrow's product yesterday. The full-time developer is very laid back and easy going, a very effective communicator, but is someone who will accept bad design if it means not rocking the boat. Code reviews or anything else that takes "time" will be out of the question - there is no way our PM will be sold on such a thing by anybody.

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  • Refactoring in domain driven design

    - by Andrew Whitaker
    I've just started working on a project and we're using domain-driven design (as defined by Eric Evans in Domain-Driven Design: Tackling Complexity in the Heart of Software. I believe that our project is certainly a candidate for this design pattern as Evans describes it in his book. I'm struggling with the idea of constantly refactoring. I know refactoring is a necessity in any project and will happen inevitably as the software changes. However, in my experience, refactoring occurs when the needs of the development team change, not as understanding of the domain changes ("refactoring to greater insight" as Evans calls it). I'm most concerned with breakthroughs in understanding of the domain model. I understand making small changes, but what if a large change in the model is necessary? What's an effective way of convincing yourself (and others) you should refactor after you obtain a clearer domain model? After all, refactoring to improve code organization or performance could be completely separate from how expressive in terms of the ubiquitous language code is. Sometimes it just seems like there's not enough time to refactor. Luckily, SCRUM lends it self to refactoring. The iterative nature of SCRUM makes it easy to build a small piece and change and it. But over time that piece will get larger and what if you have a breakthrough after that piece is so large that it will be too difficult to change? Has anyone worked on a project employing domain-driven design? If so, it would be great to get some insight on this one. I'd especially like to hear some success stories, since DDD seems very difficult to get right. Thanks!

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  • Doing powerups in a component-based system

    - by deft_code
    I'm just starting really getting my head around component based design. I don't know what the "right" way to do this is. Here's the scenario. The player can equip a shield. The the shield is drawn as bubble around the player, it has a separate collision shape, and reduces the damage the player receives from area effects. How is such a shield architected in a component based game? Where I get confused is that the shield obviously has three components associated with it. Damage reduction / filtering A sprite A collider. To make it worse different shield variations could have even more behaviors, all of which could be components: boost player maximum health health regen projectile deflection etc Am I overthinking this? Should the shield just be a super component? I really think this is wrong answer. So if you think this is the way to go please explain. Should the shield be its own entity that tracks the location of the player? That might make it hard to implement the damage filtering. It also kinda blurs the lines between attached components and entities. Should the shield be a component that houses other components? I've never seen or heard of anything like this, but maybe it's common and I'm just not deep enough yet. Should the shield just be a set of components that get added to the player? Possibly with an extra component to manage the others, e.g. so they can all be removed as a group. (accidentally leave behind the damage reduction component, now that would be fun). Something else that's obvious to someone with more component experience?

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  • Doing powerups in a component-based system

    - by deft_code
    I'm just starting really getting my head around component based design. I don't know what the "right" way to do this is. Here's the scenario. The player can equip a shield. The the shield is drawn as bubble around the player, it has a separate collision shape, and reduces the damage the player receives from area effects. How is such a shield architected in a component based game? Where I get confused is that the shield obviously has three components associated with it. Damage reduction / filtering A sprite A collider. To make it worse different shield variations could have even more behaviors, all of which could be components: boost player maximum health health regen projectile deflection etc Am I overthinking this? Should the shield just be a super component? I really think this is wrong answer. So if you think this is the way to go please explain. Should the shield be its own entity that tracks the location of the player? That might make it hard to implement the damage filtering. It also kinda blurs the lines between attached components and entities. Should the shield be a component that houses other components? I've never seen or heard of anything like this, but maybe it's common and I'm just not deep enough yet. Should the shield just be a set of components that get added to the player? Possibly with an extra component to manage the others, e.g. so they can all be removed as a group. (accidentally leave behind the damage reduction component, now that would be fun). Something else that's obvious to someone with more component experience?

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  • Overriding component behavior

    - by deft_code
    I was thinking of how to implement overriding of behaviors in a component based entity system. A concrete example, an entity has a heath component that can be damaged, healed, killed etc. The entity also has an armor component that limits the amount of damage a character receives. Has anyone implemented behaviors like this in a component based system before? How did you do it? If no one has ever done this before why do you think that is. Is there anything particularly wrong headed about overriding component behaviors? Below is rough sketch up of how I imagine it would work. Components in an entity are ordered. Those at the front get a chance to service an interface first. I don't detail how that is done, just assume it uses evil dynamic_casts (it doesn't but the end effect is the same without the need for RTTI). class IHealth { public: float get_health( void ) const = 0; void do_damage( float amount ) = 0; }; class Health : public Component, public IHealth { public: void do_damage( float amount ) { m_damage -= amount; } private: float m_health; }; class Armor : public Component, public IHealth { public: float get_health( void ) const { return next<IHealth>().get_health(); } void do_damage( float amount ) { next<IHealth>().do_damage( amount / 2 ); } }; entity.add( new Health( 100 ) ); entity.add( new Armor() ); assert( entity.get<IHealth>().get_health() == 100 ); entity.get<IHealth>().do_damage( 10 ); assert( entity.get<IHealth>().get_health() == 95 ); Is there anything particularly naive about the way I'm proposing to do this?

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  • Physics/Graphics Components

    - by Brett Powell
    I have spent the last 48 hours reading up on Object Component systems, and feel I am ready enough to start implementing it. I got the base Object and Component classes created, but now that I need to start creating the actual components I am a bit confused. When I think of them in terms of HealthComponent or something that would basically just be a property, it makes perfect sense. When it is something more general as a Physics/Graphics component, I get a bit confused. My Object class looks like this so far (If you notice any changes I should make please let me know, still new to this)... typedef unsigned int ID; class GameObject { public: GameObject(ID id, Ogre::String name = ""); ~GameObject(); ID &getID(); Ogre::String &getName(); virtual void update() = 0; // Component Functions void addComponent(Component *component); void removeComponent(Ogre::String familyName); template<typename T> T* getComponent(Ogre::String familyName) { return dynamic_cast<T*>(m_components[familyName]); } protected: // Properties ID m_ID; Ogre::String m_Name; float m_flVelocity; Ogre::Vector3 m_vecPosition; // Components std::map<std::string,Component*> m_components; std::map<std::string,Component*>::iterator m_componentItr; }; Now the problem I am running into is what would the general population put into Components such as Physics/Graphics? For Ogre (my rendering engine) the visible Objects will consist of multiple Ogre::SceneNode (possibly multiple) to attach it to the scene, Ogre::Entity (possibly multiple) to show the visible meshes, and so on. Would it be best to just add multiple GraphicComponent's to the Object and let each GraphicComponent handle one SceneNode/Entity or is the idea to have one of each Component needed? For Physics I am even more confused. I suppose maybe creating a RigidBody and keeping track of mass/interia/etc. would make sense. But I am having trouble thinking of how to actually putting specifics into a Component. Once I get a couple of these "Required" components done, I think it will make a lot more sense. As of right now though I am still a bit stumped.

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  • A design pattern for data binding an object (with subclasses) to asp.net user control

    - by Rohith Nair
    I have an abstract class called Address and I am deriving three classes ; HomeAddress, Work Address, NextOfKin address. My idea is to bind this to a usercontrol and based on the type of Address it should bind properly to the ASP.NET user control. My idea is the user control doesn't know which address it is going to present and based on the type it will parse accordingly. How can I design such a setup, based on the fact that, the user control can take any type of address and bind accordingly. I know of one method like :- Declare class objects for all the three types (Home,Work,NextOfKin). Declare an enum to hold these types and based on the type of this enum passed to user control, instantiate the appropriate object based on setter injection. As a part of my generic design, I just created a class structure like this :- I know I am missing a lot of pieces in design. Can anybody give me an idea of how to approach this in proper way.

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  • How to design database having multiple interrelated entities

    - by Sharath Chandra
    I am designing a new system which is more of a help system for core applications in banks or healthcare sector. Given the nature of the system this is not a heavy transaction oriented system but more of read intensive. Now within this application I have multiple entities which are related to each other. For e.g. Assume the following entities in the system User Training Regulations Now each of these entities have M:N Relationship with each other. Assuming the usage of a standard RDBMS, the design may involve many relationship tables each containing the relationships one other entity ("User_Training", "User_Regulations", "Training_Regulations"). This design is limiting since I have more than 3 entities in the system and maintaining the relationship graph is difficult this way. The most frequently used operation is "given an entity get me all the related entities" . I need to design the database where this operation is relatively inexpensive. What are the different recommendations for modelling this kind of database.

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  • Requesting feedback on my OO design

    - by Prog
    I'm working on an application that creates music by itself. I'm seeking feedback for my OO design so far. This question will focus on one part of the program. The application produces Tune objects, that are the final musical products. Tune is an abstract class with an abstract method play. It has two subclasses: SimpleTune and StructuredTune. SimpleTune owns a Melody and a Progression (chord sequence). It's play implementation plays these two objects simultaneously. StructuredTune owns two Tune instances. It's own play plays the two Tunes one after the other according to a pattern (currently only ABAB). Melody is an abstract class with an abstract play method. It has two subclasses: SimpleMelody and StructuredMelody. SimpleMelody is composed of an array of notes. Invoking play on it plays these notes one after the other. StructuredMelody is composed of an array of Melody objects. Invoking play on it plays these Melodyies one after the other. I think you're starting to see the pattern. Progression is also an abstract class with a play method and two subclasses: SimpleProgression and StructuredProgression, each composed differently and played differently. SimpleProgression owns an array of chords and plays them sequentially. StructuredProgression owns an array of Progressions and it's play implementation plays them sequentially. Every class has a corresponding Generator class. Tune, Melody and Progression are matched with corresponding abstract TuneGenerator, MelodyGenerator and ProgressionGenerator classes, each with an abstract generate method. For example MelodyGenerator defines an abstract Melody generate method. Each of the generators has two subclasses, Simple and Structured. So for example MelodyGenerator has a subclasses SimpleMelodyGenerator, with an implementation of generate that returns a SimpleMelody. (It's important to note that the generate methods encapsulate complex algorithms. They are more than mere factory method. For example SimpleProgressionGenerator.generate() implements an algorithm to compose a series of Chord objects, which are used to instantiate the returned SimpleProgression). Every Structured generator uses another generator internally. It is a Simple generator be default, but in special cases may be a Structured generator. Parts of this design are meant to allow the end-user through the GUI to choose what kind of music is to be created. For example the user can choose between a "simple tune" (SimpleTuneGenerator) and a "full tune" (StructuredTuneGenerator). Other parts of the system aren't subject to direct user-control. What do you think of this design from an OOD perspective? What potential problems do you see with this design? Please share with me your criticism, I'm here to learn. Apart from this, a more specific question: the "every class has a corresponding Generator class" part feels very wrong. However I'm not sure how I could design this differently and achieve the same flexibility. Any ideas?

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  • New design patterns/design strategies

    - by steven
    I've studied and implemented design patterns for a few years now, and I'm wondering. What are some of the newer design patterns (since the GOF)? Also, what should one, similar to myself, study [in the way of software design] next? Note: I've been using TDD, and UML for some time now. I'm curious about the newer paradigm shifts, and or newer design patterns.

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  • Appropriate level of granularity for component-based architecture

    - by Jon Purdy
    I'm working on a game with a component-based architecture. An Entity owns a set of Component instances, each of which has a set of Slot instances with which to store, send, and receive values. Factory functions such as Player produce entities with the required components and slot connections. I'm trying to determine the best level of granularity for components. For example, right now Position, Velocity, and Acceleration are all separate components, connected in series. Velocity and Acceleration could easily be rewritten into a uniform Delta component, or Position, Velocity, and Acceleration could be combined alongside such components as Friction and Gravity into a monolithic Physics component. Should a component have the smallest responsibility possible (at the cost of lots of interconnectivity) or should related components be combined into monolithic ones (at the cost of flexibility)? I'm leaning toward the former, but I could use a second opinion.

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  • Design Pattern Advice for Bluetooth App for Android

    - by Aimee Jones
    I’m looking for some advice on which patterns would apply to some of my work. I’m planning on doing a project as part of my college work and I need a bit of help. My main project is to make a basic Android bluetooth tracking system where the fixed locations of bluetooth dongles are mapped onto a map of a building. So my android app will regularly scan for nearby dongles and triangulate its location based on signal strength. The dongles location would be saved to a database along with their mac addresses to differentiate between them. The android phones location will then be sent to a server. This information will be used to show the phone’s location on a map of the building, or map of a route taken, on a website. My side project is to choose a suitable design pattern that could be implemented in this main project. I’m still a bit new to design patterns and am finding it hard to get my head around ones that may be suitable. I’ve heard maybe some that are aimed at web applications for the server side of things may be appropriate. My research so far is leading me to the following: Navigation Strategy Pattern Observer Pattern Command Pattern News Design Pattern Any advice would be a great help! Thanks

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  • Authorization design-pattern / practice?

    - by Lawtonfogle
    On one end, you have users. On the other end, you have activities. I was wondering if there is a best practice to relate the two. The simplest way I can think of is to have every activity have a role, and assign every user every role they need. The problem is that this gets really messy in practice as soon as you go beyond a trivial system. A way I recently designed was to have users who have roles, and roles have privileges, and activities require some combinations of privileges. For the trivial case, this is more complex, but I think it will scale better. But after I implemented it, I felt like it was overkill for the system I had. Another option would be to have users, who have roles, and activities require you to have a certain role to perform with many activities sharing roles. A more complex variant of this would given activities many possible roles, which you only needed one of. And an even more complex variant would be to allow logical statements of role ownership to use an activity (i.e. Must have A and (B exclusive or C) and must not have D). I could continue to list more, but I think this already gives a picture. And many of these have trade offs. But in software design, there are oftentimes solutions, while perhaps not perfect in every possible case, are clearly top of the pack to an extent it isn't even considered opinion based (i.e. how to store passwords, plain text is worse, hashing better, hashing and salt even better, despite the increased complexity of each level) (i.e. 2, Smart UI designs for applications are bad, even if it is subjective as to what the best design is). So, is there a best practice for authorization design that is not purely opinion based/subjective?

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  • Clean MVC design when there is viewer latency

    - by Tony Suffolk 66
    It isn't clear if this question has already been answered, so apologies in advance if this is a duplicate : I am implementing a game and trying to design around a clean MVC pattern - so my Control plane will implement the rules of the game (but not how the game is displayed), and the View plane implements how the game is displayed, and user iteraction - i.e. what game items or controls the user has activated. The challenge that I have is this : In my game the Control Plane can move game items more or less instaneously (The decision about what item to place where - and some of the initial consequences of that placement are reasonably trivial to calculate), but I want to design the Control Plane so that the View plane can display these movements either instaneously or using movement animations. The other complication is that player interaction must be locked out while those game items are moving (similar to chess - you can't attack an opposing piece as it moves past one of your pieces) So do I : Implement all the logic in the Control Plane asynchronously - and separate the descision making from the actions - so the Control plane decides piece 'A' needs to move to a given place - tells the view plane, and but does not implement the move in data until the view plane informs the control plane that the move/animation is complete. A lot of interlock points between the two layers. Implement all the control plane logic in one place - decisions and movement (keeping track of what moved where), and pass all the movements in one go to the View plane to do with what it will. Control Plane is almost fire and forget here. A hybrid of 1 & 2 - The control plane implements all the moves in a temporary data store - but maintains a second store which reflects what is actually visible to the viewer, based on calls and feedback from the View plane. All 3 are relatively easy to implement (target language is python), but having never done a clean MVC pattern with view latency before - I am not sure which design is best

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  • Organizing an entity system with external component managers?

    - by Gustav
    I'm designing a game engine for a top-down multiplayer 2D shooter game, which I want to be reasonably reuseable for other top-down shooter games. At the moment I'm thinking about how something like an entity system in it should be designed. First I thought about this: I have a class called EntityManager. It should implement a method called Update and another one called Draw. The reason for me separating Logic and Rendering is because then I can omit the Draw method if running a standalone server. EntityManager owns a list of objects of type BaseEntity. Each entity owns a list of components such as EntityModel (the drawable representation of an entity), EntityNetworkInterface, and EntityPhysicalBody. EntityManager also owns a list of component managers like EntityRenderManager, EntityNetworkManager and EntityPhysicsManager. Each component manager keeps references to the entity components. There are various reasons for moving this code out of the entity's own class and do it collectively instead. For example, I'm using an external physics library, Box2D, for the game. In Box2D, you first add the bodies and shapes to a world (owned by the EntityPhysicsManager in this case) and add collision callbacks (which would be dispatched to the entity object itself in my system). Then you run a function which simulates everything in the system. I find it hard to find a better solution to do this than doing it in an external component manager like this. Entity creation is done like this: EntityManager implements the method RegisterEntity(entityClass, factory) which registers how to create an entity if that class. It also implements the method CreateEntity(entityClass) which would return an object of type BaseEntity. Well now comes my problem: How would the reference to a component be registered to the component managers? I have no idea how I would reference the component managers from a factory/closure.

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  • Processing component pools problem - Entity Subsystem

    - by mani3xis
    Architecture description I'm creating (designing) an entity system and I ran into many problems. I'm trying to keep it Data-Oriented and efficient as much as possible. My components are POD structures (array of bytes to be precise) allocated in homogeneous pools. Each pool has a ComponentDescriptor - it just contains component name, field types and field names. Entity is just a pointer to array of components (where address acts like an entity ID). EntityPrototype contains entity name and array of component names. Finally Subsystem (System or Processor) which works on component pools. Actual problem The problem is that some components dependents on others (Model, Sprite, PhysicalBody, Animation depends on Transform component) which makes a lot of problems when it comes to processing them. For example, lets define some entities using [S]prite, [P]hysicalBody and [H]ealth: Tank: Transform, Sprite, PhysicalBody BgTree: Transform, Sprite House: Transform, Sprite, Health and create 4 Tanks, 5 BgTrees and 2 Houses and my pools will look like: TTTTTTTTTTT // Transform pool SSSSSSSSSSS // Sprite pool PPPP // PhysicalBody pool HH // Health component There is no way to process them using indices. I spend 3 days working on it and I still don't have any ideas. In previous designs TransformComponent was bound to the entity - but it wasn't a good idea. Can you give me some advices how to process them? Or maybe I should change the overall design? Maybe I should create pools of entites (pools of component pools) - but I guess it will be a nightmare for CPU caches. Thanks

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  • Can I remove the systems from a component entity system?

    - by nathan
    After reading a lot about entity/component based engines. I feel like there is no real definition for this kind of engine. Reading this thread: Implementing features in an Entity System and the linked article made me think a lot. I did not feel that comfortable using System concept so I'll write something else, inspired by this pattern. I'd like to know if you think it's a good way to organize game code and what improvements can be made. Regarding a more strict implementation of entity/component based engine, is my solution viable? Do I risk getting stuck at any point due to the lack of flexibility of this implementation (or anything else)? My engine, as for entity/component patterns has entities and components, no systems since the game logic is handled by components. Also, I think the main difference is the fact that my engine will use inherence and OOP concepts in general, I mean, I don't try to minimize them. Entity: an entity is an abstract class. It holds his position, width and height, scale and a list of linked components. The current implementation can be found here (java). Every frame, the entity will be updated (i.e all the components linked to this entity will be updated), and rendered, if a render component is specified. Component: like for entity, a component is an abstract class that must be extended to create new components. The behavior of an entity is created through his components collection. The component implementation can be found here. Components are updated when the owning entity is updated or for only one specific component (render component), rendered. Here is an example of a logic component (i.e not a renderable component, a component that's updated each frame) in charge of listening for keyboard events and a render component in charge of display a plain sprite (i.e not animated).

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  • What Every Developer Should Know About MSI Components

    - by Alois Kraus
    Hopefully nothing. But if you have to do more than simple XCopy deployment and you need to support updates, upgrades and perhaps side by side scenarios there is no way around MSI. You can create Msi files with a Visual Studio Setup project which is severely limited or you can use the Windows Installer Toolset. I cannot talk about WIX with my German colleagues because WIX has a very special meaning. It is funny to always use the long name when I talk about deployment possibilities. Alternatively you can buy commercial tools which help you to author Msi files but I am not sure how good they are. Given enough pain with existing solutions you can also learn the MSI Apis and create your own packaging solution. If I were you I would use either a commercial visual tool when you do easy deployments or use the free Windows Installer Toolset. Once you know the WIX schema you can create well formed wix xml files easily with any editor. Then you can “compile” from the wxs files your Msi package. Recently I had the “pleasure” to get my hands dirty with C++ (again) and the MSI technology. Installation is a complex topic but after several month of digging into arcane MSI issues I can safely say that there should exist an easier way to install and update files as today. I am not alone with this statement as John Robbins (creator of the cool tool Paraffin) states: “.. It's a brittle and scary API in Windows …”. To help other people struggling with installation issues I present you the advice I (and others) found useful and what will happen if you ignore this advice. What is a MSI file? A MSI file is basically a database with tables which reference each other to control how your un/installation should work. The basic idea is that you declare via these tables what you want to install and MSI controls the how to get your stuff onto or off your machine. Your “stuff” consists usually of files, registry keys, shortcuts and environment variables. Therefore the most important tables are File, Registry, Environment and Shortcut table which define what will be un/installed. The key to master MSI is that every resource (file, registry key ,…) is associated with a MSI component. The actual payload consists of compressed files in the CAB format which can either be embedded into the MSI file or reside beside the MSI file or in a subdirectory below it. To examine MSI files you need Orca a free MSI editor provided by MS. There is also another free editor called Super Orca which does support diffs between MSI and it does not lock the MSI files. But since Orca comes with a shell extension I tend to use only Orca because it is so easy to right click on a MSI file and open it with this tool. How Do I Install It? Double click it. This does work for fresh installations as well as major upgrades. Updates need to be installed via the command line via msiexec /i <msi> REINSTALL=ALL REINSTALLMODE=vomus   This tells the installer to reinstall all already installed features (new features will NOT be installed). The reinstallmode letters do force an overwrite of the old cached package in the %WINDIR%\Installer folder. All files, shortcuts and registry keys are redeployed if they are missing or need to be replaced with a newer version. When things did go really wrong and you want to overwrite everything unconditionally use REINSTALLMODE=vamus. How To Enable MSI Logs? You can download a MSI from Microsoft which installs some registry keys to enable full MSI logging. The log files can be found in your %TEMP% folder and are called MSIxxxx.log. Alternatively you can add to your msiexec command line the option msiexec …. /l*vx <LogFileName> Personally I find it rather strange that * does not mean full logging. To really get all logs I need to add v and x which is documented in the msiexec help but I still find this behavior unintuitive. What are MSI components? The whole MSI logic is bound to the concept of MSI components. Nearly every msi table has a Component column which binds an installable resource to a component. Below are the screenshots of the FeatureComponents and Component table of an example MSI. The Feature table defines basically the feature hierarchy.  To find out what belongs to a feature you need to look at the FeatureComponents table where for each feature the components are listed which will be installed when a feature is installed. The MSI components are defined in the  Component table. This table has as first column the component name and as second column the component id which is a GUID. All resources you want to install belong to a MSI component. Therefore nearly all MSI tables have a Component_ column which contains the component name. If you look e.g. a the File table you see that every file belongs to a component which is true for all other tables which install resources. The component table is the glue between all other tables which contain the resources you want to install. So far so easy. Why is MSI then so complex? Most MSI problems arise from the fact that you did violate a MSI component rule in one or the other way. When you install a feature the reference count for all components belonging to this feature will increase by one. If your component is installed by more than one feature it will get a higher refcount. When you uninstall a feature its refcount will drop by one. Interesting things happen if the component reference count reaches zero: Then all associated resources will be deleted. That looks like a reasonable thing and it is. What it makes complex are the strange component rules you have to follow. Below are some important component rules from the Tao of the Windows Installer … Rule 16: Follow Component Rules Components are a very important part of the Installer technology. They are the means whereby the Installer manages the resources that make up your application. The SDK provides the following guidelines for creating components in your package: Never create two components that install a resource under the same name and target location. If a resource must be duplicated in multiple components, change its name or target location in each component. This rule should be applied across applications, products, product versions, and companies. Two components must not have the same key path file. This is a consequence of the previous rule. The key path value points to a particular file or folder belonging to the component that the installer uses to detect the component. If two components had the same key path file, the installer would be unable to distinguish which component is installed. Two components however may share a key path folder. Do not create a version of a component that is incompatible with all previous versions of the component. This rule should be applied across applications, products, product versions, and companies. Do not create components containing resources that will need to be installed into more than one directory on the user’s system. The installer installs all of the resources in a component into the same directory. It is not possible to install some resources into subdirectories. Do not include more than one COM server per component. If a component contains a COM server, this must be the key path for the component. Do not specify more than one file per component as a target for the Start menu or a Desktop shortcut. … And these rules do not even talk about component ids, update packages and upgrades which you need to understand as well. Lets suppose you install two MSIs (MSI1 and MSI2) which have the same ComponentId but different component names. Both do install the same file. What will happen when you uninstall MSI2?   Hm the file should stay there. But the component names are different. Yes and yes. But MSI uses not use the component name as key for the refcount. Instead the ComponentId column of the Component table which contains a GUID is used as identifier under which the refcount is stored. The components Comp1 and Comp2 are identical from the MSI perspective. After the installation of both MSIs the Component with the Id {100000….} has a refcount of two. After uninstallation of one MSI there is still a refcount of one which drops to zero just as expected when we uninstall the last msi. Then the file which was the same for both MSIs is deleted. You should remember that MSI keeps a refcount across MSIs for components with the same component id. MSI does manage components not the resources you did install. The resources associated with a component are then and only then deleted when the refcount of the component reaches zero.   The dependencies between features, components and resources can be described as relations. m,k are numbers >= 1, n can be 0. Inside a MSI the following relations are valid Feature    1  –> n Components Component    1 –> m Features Component      1  –>  k Resources These relations express that one feature can install several components and features can share components between them. Every (meaningful) component will install at least one resource which means that its name (primary key to stay in database speak) does occur in some other table in the Component column as value which installs some resource. Lets make it clear with an example. We want to install with the feature MainFeature some files a registry key and a shortcut. We can then create components Comp1..3 which are referenced by the resources defined in the corresponding tables.   Feature Component Registry File Shortcuts MainFeature Comp1 RegistryKey1     MainFeature Comp2   File.txt   MainFeature Comp3   File2.txt Shortcut to File2.txt   It is illegal that the same resource is part of more than one component since this would break the refcount mechanism. Lets illustrate this:            Feature ComponentId Resource Reference Count Feature1 {1000-…} File1.txt 1 Feature2 {2000-….} File1.txt 1 The installation part works well but what happens when you uninstall Feature2? Component {20000…} gets a refcount of zero where MSI deletes all resources belonging to this component. In this case File1.txt will be deleted. But Feature1 still has another component {10000…} with a refcount of one which means that the file was deleted too early. You just have ruined your installation. To fix it you then need to click on the Repair button under Add/Remove Programs to let MSI reinstall any missing registry keys, files or shortcuts. The vigilant reader might has noticed that there is more in the Component table. Beside its name and GUID it has also an installation directory, attributes and a KeyPath. The KeyPath is a reference to a file or registry key which is used to detect if the component is already installed. This becomes important when you repair or uninstall a component. To find out if the component is already installed MSI checks if the registry key or file referenced by the KeyPath property does exist. When it does not exist it assumes that it was either already uninstalled (can lead to problems during uninstall) or that it is already installed and all is fine. Why is this detail so important? Lets put all files into one component. The KeyPath should be then one of the files of your component to check if it was installed or not. When your installation becomes corrupt because a file was deleted you cannot repair it with the Repair button under Add/Remove Programs because MSI checks the component integrity via the Resource referenced by its KeyPath. As long as you did not delete the KeyPath file MSI thinks all resources with your component are installed and never executes any repair action. You get even more trouble when you try to remove files during an upgrade (you cannot remove files during an update) from your super component which contains all files. The only way out and therefore best practice is to assign for every resource you want to install an extra component. This ensures painless updatability and repairs and you have much less effort to remove specific files during an upgrade. In effect you get this best practice relation Feature 1  –> n Components Component   1  –>  1 Resources MSI Component Rules Rule 1 – One component per resource Every resource you want to install (file, registry key, value, environment value, shortcut, directory, …) must get its own component which does never change between versions as long as the install location is the same. Penalty If you add more than one resources to a component you will break the repair capability of MSI because the KeyPath is used to check if the component needs repair. MSI ComponentId Files MSI 1.0 {1000} File1-5 MSI 2.0 {2000} File2-5 You want to remove File1 in version 2.0 of your MSI. Since you want to keep the other files you create a new component and add them there. MSI will delete all files if the component refcount of {1000} drops to zero. The files you want to keep are added to the new component {2000}. Ok that does work if your upgrade does uninstall the old MSI first. This will cause the refcount of all previously installed components to reach zero which means that all files present in version 1.0 are deleted. But there is a faster way to perform your upgrade by first installing your new MSI and then remove the old one.  If you choose this upgrade path then you will loose File1-5 after your upgrade and not only File1 as intended by your new component design.   Rule 2 – Only add, never remove resources from a component If you did follow rule 1 you will not need Rule 2. You can add in a patch more resources to one component. That is ok. But you can never remove anything from it. There are tricky ways around that but I do not want to encourage bad component design. Penalty Lets assume you have 2 MSI files which install under the same component one file   MSI1 MSI2 {1000} - ComponentId {1000} – ComponentId File1.txt File2.txt   When you install and uninstall both MSIs you will end up with an installation where either File1 or File2 will be left. Why? It seems that MSI does not store the resources associated with each component in its internal database. Instead Windows will simply query the MSI that is currently uninstalled for all resources belonging to this component. Since it will find only one file and not two it will only uninstall one file. That is the main reason why you never can remove resources from a component!   Rule 3 Never Remove A Component From an Update MSI. This is the same as if you change the GUID of a component by accident for your new update package. The resulting update package will not contain all components from the previously installed package. Penalty When you remove a component from a feature MSI will set the feature state during update to Advertised and log a warning message into its log file when you did enable MSI logging. SELMGR: ComponentId '{2DCEA1BA-3E27-E222-484C-D0D66AEA4F62}' is registered to feature 'xxxxxxx, but is not present in the Component table.  Removal of components from a feature is not supported! MSI (c) (24:44) [07:53:13:436]: SELMGR: Removal of a component from a feature is not supported Advertised means that MSI treats all components of this feature as not installed. As a consequence during uninstall nothing will be removed since it is not installed! This is not only bad because uninstall does no longer work but this feature will also not get the required patches. All other features which have followed component versioning rules for update packages will be updated but the one faulty feature will not. This results in very hard to find bugs why an update was only partially successful. Things got better with Windows Installer 4.5 but you cannot rely on that nobody will use an older installer. It is a good idea to add to your update msiexec call MSIENFORCEUPGRADECOMPONENTRULES=1 which will abort the installation if you did violate this rule.

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  • Design Book–Dimensional or No Dimensional, that is..the question

    - by drsql
    So, it is right there in the title of the book “Relational Database Design” etc (the title is kinda long :)  But as I consider what to cover and, conversely, what not to cover, dimensional design inevitably pops up. So I am considering including it in the book. One thing I try to do is to cover topics to a level where you can start using it immediately, and I am not sure that I could get a deep enough coverage of the subject to do that. I don’t really feel like it has to be the definitive source...(read more)

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  • Recommendations for books and training resources covering for Design for Programmers

    - by Jon Hopkins
    Off the back of one of the answers to this question (currently the second highest scoring), it made me think, what's the best way to get developers up to speed on good basic design principals. I'm not talking about making them into graphic designers but some developers almost take pride in ugly UIs, seeing them as unimportant next to the functionality. What primarily interested in are the graphic design elements rather than the usability aspects which is pretty well covered by books such as Don't Make Me Think. Use of white space, emphasis, font selection and a million other things I'm probably not even aware of. I know people are often seen as artistic or not artistic but surely the basics can be taught and someone has written a book covering this?

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  • Is this proper OO design for C++?

    - by user121917
    I recently took a software processes course and this is my first time attempting OO design on my own. I am trying to follow OO design principles and C++ conventions. I attempted and gave up on MVC for this application, but I am trying to "decouple" my classes such that they can be easily unit-tested and so that I can easily change the GUI library used and/or the target OS. At this time, I have finished designing classes but have not yet started implementing methods. The function of the software is to log all packets sent and received, and display them on the screen (like WireShark, but for one local process only). The software accomplishes this by hooking the send() and recv() functions in winsock32.dll, or some other pair of analogous functions depending on what the intended Target is. The hooks add packets to SendPacketList/RecvPacketList. The GuiLogic class starts a thread which checks for new packets. When new packets are found, it utilizes the PacketFilter class to determine the formatting for the new packet, and then sends it to MainWindow, a native win32 window (with intent to later port to Qt).1 Full size image of UML class diagram Here are my classes in skeleton/header form (this is my actual code): class PacketModel { protected: std::vector<byte> data; int id; public: PacketModel(); PacketModel(byte* data, unsigned int size); PacketModel(int id, byte* data, unsigned int size); int GetLen(); bool IsValid(); //len >= sizeof(opcode_t) opcode_t GetOpcode(); byte* GetData(); //returns &(data[0]) bool GetData(byte* outdata, int maxlen); void SetData(byte* pdata, int len); int GetId(); void SetId(int id); bool ParseData(char* instr); bool StringRepr(char* outstr); byte& operator[] (const int index); }; class SendPacket : public PacketModel { protected: byte* returnAddy; public: byte* GetReturnAddy(); void SetReturnAddy(byte* addy); }; class RecvPacket : public PacketModel { protected: byte* callAddy; public: byte* GetCallAddy(); void SetCallAddy(byte* addy); }; //problem: packets may be added to list at any time by any number of threads //solution: critical section associated with each packet list class Synch { public: void Enter(); void Leave(); }; template<class PacketType> class PacketList { private: static const int MAX_STORED_PACKETS = 1000; public: static const int DEFAULT_SHOWN_PACKETS = 100; private: vector<PacketType> list; Synch synch; //wrapper for critical section public: void AddPacket(PacketType* packet); PacketType* GetPacket(int id); int TotalPackets(); }; class SendPacketList : PacketList<SendPacket> { }; class RecvPacketList : PacketList<RecvPacket> { }; class Target //one socket { bool Send(SendPacket* packet); bool Inject(RecvPacket* packet); bool InitSendHook(SendPacketList* sendList); bool InitRecvHook(RecvPacketList* recvList); }; class FilterModel { private: opcode_t opcode; int colorID; bool bFilter; char name[41]; }; class FilterFile { private: FilterModel filter; public: void Save(); void Load(); FilterModel* GetFilter(opcode_t opcode); }; class PacketFilter { private: FilterFile filters; public: bool IsFiltered(opcode_t opcode); bool GetName(opcode_t opcode, char* namestr); //return false if name does not exist COLORREF GetColor(opcode_t opcode); //return default color if no custom color }; class GuiLogic { private: SendPacketList sendList; RecvPacketList recvList; PacketFilter packetFilter; void GetPacketRepr(PacketModel* packet); void ReadNew(); void AddToWindow(); public: void Refresh(); //called from thread void GetPacketInfo(int id); //called from MainWindow }; I'm looking for a general review of my OO design, use of UML, and use of C++ features. I especially just want to know if I'm doing anything considerably wrong. From what I've read, design review is on-topic for this site (and off-topic for the Code Review site). Any sort of feedback is greatly appreciated. Thanks for reading this.

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  • Design Pattern for Complex Data Modeling

    - by Aaron Hayman
    I'm developing a program that has a SQL database as a backing store. As a very broad description, the program itself allows a user to generate records in any number of user-defined tables and make connections between them. As for specs: Any record generated must be able to be connected to any other record in any other user table (excluding itself...the record, not the table). These "connections" are directional, and the list of connections a record has is user ordered. Moreover, a record must "know" of connections made from it to others as well as connections made to it from others. The connections are kind of the point of this program, so there is a strong possibility that the number of connections made is very high, especially if the user is using the software as intended. A record's field can also include aggregate information from it's connections (like obtaining average, sum, etc) that must be updated on change from another record it's connected to. To conserve memory, only relevant information must be loaded at any one time (can't load the entire database in memory at load and go from there). I cannot assume the backing store is local. Right now it is, but eventually this program will include syncing to a remote db. Neither the user tables, connections or records are known at design time as they are user generated. I've spent a lot of time trying to figure out how to design the backing store and the object model to best fit these specs. In my first design attempt on this, I had one object managing all a table's records and connections. I attempted this first because it kept the memory footprint smaller (records and connections were simple dicts), but maintaining aggregate and link information between tables became....onerous (ie...a huge spaghettified mess). Tracing dependencies using this method almost became impossible. Instead, I've settled on a distributed graph model where each record and connection is 'aware' of what's around it by managing it own data and connections to other records. Doing this increases my memory footprint but also let me create a faulting system so connections/records aren't loaded into memory until they're needed. It's also much easier to code: trace dependencies, eliminate cycling recursive updates, etc. My biggest problem is storing/loading the connections. I'm not happy with any of my current solutions/ideas so I wanted to ask and see if anybody else has any ideas of how this should be structured. Connections are fairly simple. They contain: fromRecordID, fromTableID, fromRecordOrder, toRecordID, toTableID, toRecordOrder. Here's what I've come up with so far: Store all the connections in one big table. If I do this, either I load all connections at once (one big db call) or make a call every time a user table is loaded. The big issue here: the size of the connections table has the potential to be huge, and I'm afraid it would slow things down. Store in separate tables all the outgoing connections for each user table. This is probably the worst idea I've had. Now my connections are 'spread out' over multiple tables (one for each user table), which means I have to make a separate DB called to each table (or make a huge join) just to find all the incoming connections for a particular user table. I've avoided making "one big ass table", but I'm not sure the cost is worth it. Store in separate tables all outgoing AND incoming connections for each user table (using a flag to distinguish between incoming vs outgoing). This is the idea I'm leaning towards, but it will essentially double the total DB storage for all the connections (as each connection will be stored in two tables). It also means I have to make sure connection information is kept in sync in both places. This is obviously not ideal but it does mean that when I load a user table, I only need to load one 'connection' table and have all the information I need. This also presents a separate problem, that of connection object creation. Since each user table has a list of all connections, there are two opportunities for a connection object to be made. However, connections objects (designed to facilitate communication between records) should only be created once. This means I'll have to devise a common caching/factory object to make sure only one connection object is made per connection. Does anybody have any ideas of a better way to do this? Once I've committed to a particular design pattern I'm pretty much stuck with it, so I want to make sure I've come up with the best one possible.

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