Design patterns: what exactly are "component-based software systems"?

Component-based software is made of interactive components, where each component has a clear interface and is independent and replaceable. Therefore, the components can be developed independently of each other and can be reused in all projects.

This component-based approach stems from systems engineering: systems break down into subsystems, which are subdivided into components and even subcomponents, if complexity requires it. Component-based development is therefore suitable for very large developments.

Software that is not component based is, for example:

  • systems made of spaghetti code
  • non-modular systems that separate data structures from code.
  • Great monolithic system made of many interdependent and coupled parts, which might look like components but are not really independent or replaceable.

Today, with OO programming and the popularity of good design practices, many developments are based on components.

Character design behavior (question about the Unicode standard)

I have been reading the Unicode core specification (see https://www.unicode.org/versions/latest/). I mainly understood what the text explained in the section 2.1 Architectural context until he started talking about design behaviors. There seems to be no preface or explanation of the phrase & # 39; character design behavior & # 39 ;.

Section 2.1 explains how a character encoding should be designed taking into account text processes and algorithms, since an encoding choice can make text representation and other processes more complex (or simpler, depending on the choice) .

The specification then continues with a Identify character subtitle that uses multiple phrases, including the word & # 39; design & # 39 ;. Here are some examples of the text:

  • "Every time Unicode makes statements about the default value character design behavior, is done to ensure that users … "
  • "The actual design in an implementation it may differ in detail. "
  • "A mathematician design system, .., you will have many domain-specific rules for design.. "
  • "The purpose of defining the default Unicode value design behavior it is not enforcing a unique and specific aesthetic design for each script .. "

What does & # 39; design & # 39; and / or & # 39; character design behavior & # 39; in this context?

Multiple Threading: Is my server's design safe with respect to multiple threads and concurrent database reads / writes?

I am creating a chat server using sockets and a MySQL database, and after it works, I want to expand it to make it a more complex game server.

I want to know if my design is missing something.

Specifically, I am concerned about accessing the database from different threads, or if I may be creating too many threads and if there is likely to be a bottleneck somewhere.

I have 3 functions:

principal function start a second thread for the ServerHandler function that repeats and accepts new customer connections. That ServerHandler function then opens a new thread for each client connection for a ClientHandler function.

The code / pseudocode (so far incomplete while I am still considering the architecture) is below. I am writing it in Scala.

My main questions are about the ClientHandler function and if I am doing something in the wrong order. Will I be at risk of separate client threads performing database writes and reads in an unexpected order that cause irreproducible problems?

I wonder if I need a separate thread with a list of commands to execute, so I can be sure that 1 client writes and then reads, then another client writes and then reads, etc. Do I need to maintain a read / write list of the database? Or does the database server handle it in some way?

Mainly, I would like to be aware of my lack of understanding of database readings / writes in different threads, and if there is something obvious that I am doing wrong here. Does the design of the program structure look good?

With regard to threads, will I have to test the server with many client connections (1k, 10k, 100k?) And then set some client connection limit to what I think is safe?

// ** ClientHandler **
// This is run in a new thread for each client that connects to the ServerHandler
// This does:
// 1. Set up input and output streams to communicate with 1 client
// 2. Set up connection to database (MySQL server running on the same machine), including:
//    a. Establish connection
//    b. Read some data from the database (latest version #, # of clients connected, etc)
// 3. Send welcome message to client (latest version #, # of clients connected, etc)
// 4. Set "startTime" variable to current system time in milliseconds to detect client timeout
// 5. Loop and do this (nothing is blocking, so irrelevant steps will be skipped):
//    1. Handle client message (if there is a new one), including:
//       a. Parse client message, including:
//          i. If we have not verified the client yet, we only accept one command: "connect"
//          ii. On "connect", we verify the ID and update the database (most recent log in time)
//       b. Database reads/writes/updates as necessary, depending on the command
//       c. Send a response message back to the client with the results
//    Even if there is no client message received, we do this:
//    2. Check for server-side updates that should be notified to the client, including:
//       a. Database reads
//       b. Timestamp comparisons, checking when we last notified the client of the server state
//    3. Notify client of any server-side state changes (if necessary)
// 6. If the client times out (~5000ms), update the database that the client has disconnected
// 7. Close database connection
// 8. Close socket
ClientHandler(socket){
    // Set up input and output streams to communicate with 1 client
    val inputstream = new BufferedReader(new InputStreamReader(socket.getInputStream()))
    val outputstream = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()))

    // Set up connection to database (MySQL server running on the same machine)
    val db = Database.forConfig("mydb")
    // Read some data from the database (latest version #, # of clients connected, etc)
    ...

    // Send welcome message to client (latest version #, # of clients connected, etc)
    outputstream.write(...).newLine().flush()

    // Set "startTime" variable to current system time in milliseconds to detect client timeout
    var startTime = System.currentTimeMillis()

    //
    ...
}

// ** ServerHandler **
// This runs once in its own thread (because it contains a blocking call)
// This creates a new thread to run ClientHandler for each client that connects
ServerHandler(server_socket){
    while(true){
        val socket = server_socket.accept() // this is a blocking call
        val client_handler = new ClientHandler(socket)
        val thread = new Thread(client_handler)
        thread.start() // when a client connects, start a new thread to handle that client
    }
}

// ** main **
// This does 3 things:
// 1. Start a new thread for ServerHandler which sits and waits for clients to connect
// 2. Loop and accept commands from admin via console
// 3. Process server-side logic in real-time
main{
    // Start a new thread for ServerHandler
    val server_socket = new ServerSocket(port 10000)
    val server_handler = new ServerHandler(server_socket)
    val thread = new Thread(server_handler)
    thread.start() // start a thread for the server handler

    // Loop and accept commands from admin via console
    while(true){
        input match{
            case "stats" =>
                // print stats (# of clients logged in etc)
            case "quit" =>
                // close server_socket etc and stop program
            case _ =>
                // unrecognized command
        }
    }
}

design patterns: management of aggregations of monthly transactions of several servers

Context: A system tracks some type of transaction for its entire user base. At the end of the month, each entity capable of receiving transactions must be sent exactly an invoice containing all the transactions of the current month.
This system has one instance, which means that there are several instances (servers) of the system running.

How to handle this type of scenario? I should not allow duplicate monthly transaction evaluations. Given the nature of the system, a master-slave architecture is discarded, since the master or master-slave choice in general does not scale to a large number of cases.

I would like to distribute the burden of aggregating monthly transactions in all instances of execution. Transactions are stored in a database in the form (user_id, id_transmission_id, amount_transmission). The aggregation of failed monthly transactions must be retry by another instance

In summary: I need exactly one-time guarantees for a distributed system without a master-slave concept

What http error to return in case of validation and commercial rules in a domain-directed design API

I have a .net core API that tries to implement it according to the design principles of the domain unit.

In the domain layer there is an audience Create Method that contains all the validation and commercial rules. If one fails, it will throw an exception. Basically, you cannot create an invalid entity or an invalid value type. For example:

public class Adult
{
   private Adult(string name,int age)
   {
       this.Name = name;
       this.Age = age;
   }

   public string Name { get; }

   public int Age { get; }

   public static Adult Create(string name, int age)
   {
      if (string.IsNullOrWhiteSpace(name))
          throw new ArgumentException(nameof(name));

      if (age < 18)
         throw new ArgumentException("age should not be less that 18");

     return new Adult(name, age);
 }

}

In the web layer, my web data has the basic validation attributes. For example:

public class AdultWebDto
{
   (Required)
   public string Name {get; set; }

   public int Age {get; set; }
}

Basically, if the user tries to create an unnamed adult, it will return a 400 error, but if he tries to create a user with an age under 18, he will pass the dto validation and return a 500 error.

Of course, if the user requests an Adult with an invalid name or age, he will return an error 500 since the data coming from the repository was invalid.

Is it what I am doing well? So, for simple validation rules to verify that in the web layer and return a 400 error but in the case of more complicated business rules to return a 500 error?

How can I improve my design with this content here?

I am designing a website that has a user interface as below as of now. In this, I feel that there is something that is not right with the space between the content on the left.

As I am a newbie in design. Can anyone help me with the correct spacing and design?

enter the description of the image here

DESIGN OF WEB SITES AND CREATION OF APPLICATIONS for $ 100

DESIGN OF WEB SITES AND CREATION OF APPLICATIONS

We make many websites and applications. And in addition, we also help create malware and viruses. We carry out legal cyber attacks on websites and much more, but we only focus on creating websites and applications.

.

Object-oriented design: what are some easy-to-use tools for prototyping conceptual data models?

I am in the initial stages of planning a potentially large project, and I am looking to create prototypes of the basic data structures involved before getting stuck in the coding of all behavior / logic.

Ideally, I am looking for a GUI application with a declarative interface that allows me to define arbitrary data types, specify hierarchical relationships between them, store instances / records of those custom types and export these models / data sets in a tabular / serialized file formats .

I have considered writing JSON or YAML in a text editor or using a spreadsheet application to approximate a relational database, but none of the approaches really do a great job of capturing / visualizing relationships between objects. That makes sense considering that the serialization of data is the point of JSON and YAML, and a drawback of relational databases is that the associative tables are much less readable than simply having a nested / embedded list in the object's record. principal.

I am aware that there are many conceptual / mental mapping tools, but as far as I can tell, they tend to be less structured than I am looking for as a general rule. Is it time to choose a suitable modeling language like UML / SysML, or is it exaggerated if I am not looking to model any behavior? The only thing that comes closest to me is like a kind of wiki in which you can define templates for different types of records and link between records / instances of those types, but obviously I don't want to mess with all the HTML headaches if I don't I need it.

Obviously, my code will eventually be the real representation of this data model, but is there a quick and convenient visual tool for prototyping these kinds of things that I am missing?

web design services for small businesses

The administrations of the architecture of our website are not the same size: there are no clipping agreements, in any case, not from the best organizations. A decent web architecture office will help you make sense of the best type of site for your business. What is significant is that its site is excellent, insightfully extended and focused on lead. In addition, you must constantly update it to be aware of the cutting edge customer's wishes. Most web architectures only have a future of 2 to 5 years.

Also read: Website design that won't ruin the bank