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SOA (Principles (Modular (services should be modular and loosely coupled,…

- - - - In object oriented programming, loose coupling is achieved by only exposing the relevant elements of a class or component to its client. In service oriented architecture, requests are made by passing communication to the service in a way that aligns with its interface
  - - - Using services in combination is like composing objects in an object oriented programming paradigm. Just like objects can be combined to provide the desired behavior so too can services in SOA
  - - - Distributed applications using web services have standards like UDDI, which stands for Universal Description, Discovery and Integration to connect service providers with potential service requesters.
- - - - he HTTP status code, which informs the client the status of the request
      - HTTP request must indicate a request method in its request line
        
        The GET method retrieves the resource given by the URI provided in the request line. For example, this could retrieve a webpage, image, or, if a program is specified as the resource, it could retrieve the output of this program
        
        Suppose you want to view a campsite reservation you previously made on camping.com. At the time of booking, you were given the reservation number 17021. To review your booking, you must send this URL-encoded query string to camping.com/reservation
        
        The POST method is intended to be used to add or modify the resource according to the message body of the request on the host specified in the URI of the request. That is, the message body contains the information that will be used to create or update a resource on the website
        
        HTML forms often use POST requests to submit data. If the data in the message body is from an HTML form, then, like a GET query, it is URL-encoded
        
        The PUT method takes the information provided in the body of the request and creates or updates a resource at the location specified in the URI of the request
        
        We will again build off of our camping trip example. You realize that you don't have an axe or wood, but would like to have a campfire during your trip. Thankfully, the website allows you to add a note about your reservation for the campsite staff. Since your reservation already exists on the website and you know where to access its information using your reservation number, to add a note you simply need to make a PUT request to that location. The note would be a JSON object and delivered in the body of request
    - - Two headers that must be included in any request are
        
        the host header that contains the domain name or IP address of the host and the accept header to inform the server what kinds of content the client will accept as a response
    - - may be an HTML document, JSON, encoded parameters, etc.
  - - - When your browser accesses a URI that starts with HTTP, a connection between your web browser and a web server is opened on TCP port 80,
  - - - Special or unsafe characters, like space or Unicode, require you to encode these characters. Usually, unsafe characters are replaced with a percent sign, followed by their two digit hexadecimal digit encoding.
  - - - For example, if you are browsing an online shopping website and clicking on items, the HTTP protocol does not keep track of which items you've previously clicked. Each time you click another item, a new request is sent. But the protocol is not aware if the same client is making the request
      - A website can use HTTP cookies to track the behavior of shoppers on their site. The first time a client makes a request, the site gives them an HTTP cookie to store information about the client's browsing session. The cookie is stored by the client and updated by the server each time the client makes a request to the server. This allows a server to store state information about interactions with this client, which can be useful for tracking purposes
- - - - is the basis for middleware systems used for certain web services. RPC was designed specifically as a middleware component for networked systems and has been extended to improve its flexibility and usability.
        
        As the name implies, a remote procedure call allows clients to invoke procedures that are implemented on a server
        
        see images
        
        RPC was originally designed to be synchronous. During a remote procedure call, the client component will pause its execution while we wait for a response. This is also known as blocking since the client cannot perform any other task until the server returns a result
        
        it evolved into Object Brokers for middleware
        
        Object brokers combined the distributed computing aspects of remote procedure calls with object oriented design principles. By including object oriented programming, object brokers simplify and allow distributed systems to use an object oriented approach.
        
        CORBA, see image
    - - See image
        
        As systems move towards n-tier architectures, middleware needs to be able to encapsulate more functionalities, from business logic and distribution of client requests to being involved in handling authentication and authorization.