Introduction to JavaScript Object Notation (JSON) in JavaScript and .NET

JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. It is based on a subset of the JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language.
JSON is built on two structures:

• A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
• An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.

These are universal data structures. Virtually all modern programming languages support them in one form or another. It makes sense that a data format that is interchangeable with programming languages also be based on these structures.
In JSON, they take on these forms:
An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).

An array is an ordered collection of values. An array begins with [ (left bracket) and ends with ] (right bracket). Values are separated by , (comma).

A value can be a string in double quotes, or a number, or true or false or null, or an object or an array. These structures can be nested.

A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A character is represented as a single character string. A string is very much like a C or Java string.

A number is very much like a C or Java number, except that the octal and hexadecimal formats are not used.

Whitespace can be inserted between any pair of tokens. Excepting a few encoding details, that completely describes the language.

WCF Architecture

Contracts

Contracts layer are next to that of Application layer. Developer will directly use this contract to develop the service. We are also going to do the same now. Let us see briefly what these contracts will do for us and we will also know that WCF is working on message system.

Service contracts

- Describe about the operation that service can provide. Example, Service provided to know the temperature of the city based on the zip code, this service we call as Service contract. It will be created using Service and Operational Contract attribute.

Data contract

- It describes the custom data type which is exposed to the client. This defines the data types, are passed to and from service. Data types like int, string are identified by the client because it is already mention in XML schema definition language document, but custom created class or datatype cannot be identified by the client e.g. Employee data type. By using DataContract we can make client aware that we are using Employee data type for returning or passing parameter to the method.

Message Contract

- Default SOAP message format is provided by the WCF runtime for communication between Client and service. If it is not meeting your requirements then we can create our own message format. This can be achieved by using Message Contract attribute.

Policies and Binding

- Specify conditions required to communicate with a service e.g security requirement to communicate with service, protocol and encoding used for binding.

Service Runtime

- It contains the behaviors that occur during runtime of service.

• Throttling Behavior- Controls how many messages are processed.
• Error Behavior - Specifies what occurs, when internal error occurs on the service.
• Metadata Behavior - Tells how and whether metadata is available to outside world.
• Instance Behavior - Specifies how many instance of the service has to be created while running.
• Transaction Behavior - Enables the rollback of transacted operations if a failure occurs.
• Dispatch Behavior - Controls how a message is processed by the WCF Infrastructure.

Messaging

- Messaging layer is composed of channels. A channel is a component that processes a message in some way, for example, by authenticating a message. A set of channels is also known as a channel stack. Channels are the core abstraction for sending message to and receiving message from an Endpoint. Broadly we can categories channels as

• Transport Channels
  Handles sending and receiving message from network. Protocols like HTTP, TCP, name pipes and MSMQ.
• Protocol Channels
  Implements SOAP based protocol by processing and possibly modifying message. E.g. WS-Security and WS-Reliability.

Activation and Hosting

- Services can be hosted or executed, so that it will be available to everyone accessing from the client. WCF service can be hosted by following mechanism

• IIS
  Internet information Service provides number of advantages if a Service uses Http as protocol. It does not require Host code to activate the service, it automatically activates service code.
• Windows Activation Service
  (WAS) is the new process activation mechanism that ships with IIS 7.0. In addition to HTTP based communication, WCF can also use WAS to provide message-based activation over other protocols, such as TCP and named pipes.
• Self-Hosting
  WCF service can be self hosted as console application, Win Forms or WPF application with graphical UI.
• Windows Service
  WCF can also be hosted as a Windows Service, so that it is under control of the Service Control Manager (SCM).

What's the difference between override and new

This is all to do with polymorphism. When a virtual method is called on a reference, the actual type of the object that the reference refers to is used to decide which method implementation to use. When a method of a base class is overridden in a derived class, the version in the derived class is used, even if the calling code didn't "know" that the object was an instance of the derived class. For instance: public class Base { public virtual void SomeMethod() { } } public class Derived : Base { public override void SomeMethod() { } } ... Base b = new Derived(); b.SomeMethod(); will end up calling Derived.SomeMethod if that overrides Base.SomeMethod. Now, if you use the new keyword instead of override, the method in the derived class doesn't override the method in the base class, it merely hides it. In that case, code like this: public class Base { public virtual void SomeOtherMethod() { } } public class Derived : Base { public new void SomeOtherMethod() { } } ... Base b = new Derived(); Derived d = new Derived(); b.SomeOtherMethod(); d.SomeOtherMethod(); Will first call Base.SomeOtherMethod (line 3), then Derived.SomeOtherMethod (line 4). They're effectively two entirely separate methods which happen to have the same name, rather than the derived method overriding the base method. If you don't specify either new or overrides, the resulting output is the same as if you specified new, but you'll also get a compiler warning (as you may not be aware that you're hiding a method in the base class method, or indeed you may have wanted to override it, and merely forgot to include the keyword). That provides the basics of overriding and the difference between new and override, but you should really see a book or tutorial for a more in-depth look at polymorphism.

Components of .Net Framework 3.5

(1) Common Language Runtime or CLR It performs memory management, exception handling, debugging, security checking, thread execution, code execution, code safety, verification and compilation.Those codes which are directly managed by the CLR are called the managed code. When the managed code is compiled, the compiler converts the source code into a CPU independent intermediate language (IL) code. A Just in time compiler (JIT) compiles the IL code into native code, which is CPU specific.

(2) .Net Framework Class Library It contains a huge library of reusable types . classes, interfaces, structures and enumerated values, which are collectively called types.

(3) Common Language Specification It contains the specifications for the .Net supported languages and implementation of language integration.

(4) Common Type System It provides guidelines for declaring, using and managing types at runtime, and cross-language communication.

Metadata and Assemblies Metadata is the binary information describing the program, which is either stored in a portable executable file (PE) or in the memory. Assembly is a logical unit consisting of the assembly manifest, type metadata, IL code and set of resources like image files etc.

(5) Windows Forms This contains the graphical representation of any window displayed in the application.

(6) ASP.Net and ASP.Net AJAX ASP.Net is the web development model and AJAX is an extension of ASP.Net for developing and implementing AJAX functionality. ASP.Net AJAX contains the components that allow the developer to update data on a website without a complete reload of the page.

(7) ADO.Net It is the technology used for working with data and databases. It provides accesses to data sources like SQL server, OLE DB, XML etc. The ADO .Net allows connection to data sources for retrieving, manipulating and updating data.

(8) Windows Workflow Foundation (WF) It helps in building workflow based applications in Windows. It contains activities, workflow runtime, workflow designer and a rules engine.

(9)Windows Presentation Foundation It provides a separation between the user interface and the business logic. It helps in developing visually stunning interfaces using documents, media, two and three dimensional graphics, animations and more.

(10) Windows Communication Foundation (WCF) It is the technology used for building and running connected systems.

(11) Windows CardSpace It provides safety of accessing resources and sharing personal information on the internet.

(12) LINQ It imparts data querying capabilities to .Net languages using a syntax which is similar to the tradition query language SQL.