.NET Framework

 

Developer:                     Microsoft

Latest release:               Version 3.0 / November 6, 2006

OS:                                 Windows XP SP2 and above

Use:                                System platform

License:                         Proprietary software

Website:                        www.microsoft.com/net/

 

 

 

The Microsoft .NET Framework is a software component that can be added to the Microsoft Windows operating system. It provides a large body of pre-coded solutions to common program requirements, and manages the execution of programs written specifically for the framework. The .NET Framework is a key Microsoft offering, and is intended to be used by most new applications created for the Windows platform.

 

The pre-coded solutions form the framework's class library and cover a large range of programming needs in areas including the user interface, data access, cryptography, web application development, numeric algorithms, and network communications. The functions of the class library are used by programmers who combine them with their own code to produce applications.

 

Programs written for the .NET Framework execute in a software environment that manages the program's runtime requirements. This runtime environment, which is also a part of the .NET Framework, is known as the Common Language Runtime (CLR). The CLR provides the appearance of an application virtual machine, so that programmers need not consider the capabilities of the specific CPU that will execute the program. The CLR also provides other important services such as security mechanisms, memory management, and exception handling. The class library and the CLR together compose the .NET Framework. The framework is intended to make it easier to develop computer applications and to reduce the vulnerability of applications and computers to security threats.

 

First released in 2002, it is included with Windows Server 2003 and Windows Vista, and can be installed on most older versions of Windows.

 

Significance

 

For software developers, the .NET Framework is a significant change. It brings into the operating system features and responsibilities that previously had been provided individually by programming languages and tools from various sources. The incorporation of the features into the operating system is meant to provide a number of advantages, including:

Assuring the availability of framework features to all programs written in any of the .NET languages.

Providing to programmers a common means of accessing framework features, regardless of programming language.

Guarantees of a common behavior within the framework, regardless of programming language.

Allowing the operating system to provide some guarantees of program behavior that it otherwise could not offer.

Reducing the complexity and limitations of program-to-program communication, even when those programs are written in different .NET languages.

 

 

 

Rationale

 

 

 

 

The creation of the .NET Framework reflects what has been learned over the years about the typical challenges that programmers face and useful approaches to those challenges.

 

Individual programming languages and tools led the way in proving the viability of features such as strong data typing, garbage-collected memory management, exception-based error handling, virtual machine architectures, and comprehensive class libraries. Visual Basic, Powerbuilder, the C++ Standard Template Library (STL), and other languages each implemented at least some of these features, but the Java language and its frameworks J2SE and J2EE became the most notable competitive threat to Microsoft[1]. After failed attempts (due to copyright issues [2][3]) to include a modified form of Java with Windows, Microsoft set out to create its own products that incorporated the best features of that and other languages. The effort resulted in the Microsoft .NET Framework and its accompanying programming languages and tools.

 

Design goals and principal features

 

 

 

 

 

 

 

 

The .NET Framework was designed with several intentions:

Interoperability - Because interaction between new and older applications is commonly required, the .NET Framework provides means to access functionality that is implemented in programs that execute outside the .NET environment. Access to COM components is provided in the EnterpriseServices namespace of the framework, and access to other functionality is provided using the P/Invoke feature.

· Common Runtime Engine - Programming languages on the .NET Framework compile into an intermediate language known as the Common Intermediate Language, or CIL; Microsoft's implementation of CIL is known as Microsoft Intermediate Language, or MSIL. In Microsoft's implementation, this intermediate language is not interpreted, but rather compiled in a manner known as just-in-time compilation (JIT) into native code. The combination of these concepts is called the Common Language Infrastructure (CLI), a specification; Microsoft's implementation of the CLI is known as the Common Language Runtime (CLR).

· Language Independence - The .NET Framework introduces a Common Type System, or CTS. The CTS specification defines all possible datatypes and programming constructs supported by the CLR and how they may or may not interact with each other. Because of this feature, the .NET Framework supports development in multiple programming languages. This is discussed in more detail in the .NET languages section below.

· Base Class Library - The Base Class Library (BCL), sometimes referred to as the Framework Class Library (FCL), is a library of types available to all languages using the .NET Framework. The BCL provides classes which encapsulate a number of common functions, including file reading and writing, graphic rendering, database interaction and XML document manipulation.

· Simplified Deployment - Installation of computer software must be carefully managed to ensure that it does not interfere with previously installed software, and that it conforms to increasingly stringent security requirements. The .NET framework includes design features and tools that help address these requirements.

· Security - .NET allows for code to be run with different trust levels without the use of a separate sandbox.

 

The design of the .NET Framework is such that it supports platform independence. That is, a program written to use the framework should run without change on any type of computer for which the framework is implemented. At present, Microsoft has implemented the full framework only on the Windows operating system. Microsoft and others have implemented portions of the framework on non-Windows systems, but to date those implementations are neither complete nor widely used.

 

.NET Framework architecture

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                       Visual overview of the Common Language Infrastructure (CLI)

 

 

Common Language Infrastructure (CLI)

 

The most important component of the .NET Framework lies in the Common Language Infrastructure, or CLI. The purpose of the CLI is to provide a language-agnostic platform for application development and execution, including, but not limited to, components for exception handling, garbage collection, security, and interoperability. Microsoft's implementation of the CLI is called the Common Language Runtime, or CLR. The CLR is composed of five primary parts:

 

· Common Type System (CTS)

· Common Language Specification (CLS)

· Common Intermediate Language (CIL)

· Just-in-Time Compiler (JIT)

· Virtual Execution System (VES)

 

Assemblies

 

The intermediate MSIL code is housed in .NET assemblies, which for the Windows implementation means a Portable Executable (PE) file (EXE or DLL). Assemblies are the .NET unit of deployment, versioning and security. The assembly consists of one or more files, but one of these must contain the manifest, which has the metadata for the assembly. The complete name of an assembly contains its simple text name, version number, culture and public key token; it must contain the name, but the others are optional. The public key token is generated when the assembly is created, and is a value that uniquely represents the name and contents of all the assembly files, and a private key known only to the creator of the assembly. Two assemblies with the same public key token are guaranteed to be identical. If an assembly is tampered with (for example, by hackers), the public key can be used to detect the tampering.

 

Metadata

 

All CIL is self-describing through .NET metadata. The CLR checks on metadata to ensure that the correct method is called. Metadata is usually generated by language compilers but developers can create their own metadata through custom attributes.

 

Base Class Library (BCL)

 

The Base Class Library (BCL), sometimes incorrectly referred to as the Framework Class Library (FCL) (which is a superset including the Microsoft.* namespaces), is a library of classes available to all languages using the .NET Framework. The BCL provides classes which encapsulate a number of common functions such as file reading and writing, graphic rendering, database interaction, XML document manipulation, and so forth. The BCL is much larger than other libraries, but has much more functionality in one package.

 

Security

 

.NET has its own security mechanism, with two general features: Code Access Security (CAS), and validation and verification. Code Access Security is based on evidence that is associated with a specific assembly. Typically the evidence is the source of the assembly (whether it is installed on the local machine, or has been downloaded from the intranet or Internet). Code Access Security uses evidence to determine the permissions granted to the code. Other code can demand that calling code is granted a specified permission. The demand causes the CLR to perform a call stack walk: every assembly of each method in the call stack is checked for the required permission and if any assembly is not granted the permission then a security exception is thrown.

 

When an assembly is loaded the CLR performs various tests. Two such tests are validation and verification. During validation the CLR checks that the assembly contains valid metadata and CIL, and it checks that the internal tables are correct. Verification is not so exact. The verification mechanism checks to see if the code does anything that is 'unsafe'. The algorithm used is quite conservative and hence sometimes code that is 'safe' is not verified. Unsafe code will only be executed if the assembly has the 'skip verification' permission, which generally means code that is installed on the local machine.

 

Standardization and Licensing

 

In August, 2000, Microsoft, Hewlett-Packard, and Intel worked to standardize CLI and the C# programming language. By December, 2001, both were ratified ECMA standards (ECMA 335 and ECMA 334). ISO followed in April, 2003 (ISO/IEC 23271 and ISO/IEC 23270).

 

While Microsoft and their partners hold patents for CLI and C#, ECMA and ISO requires that all patents essential to implementation be made available under "reasonable and non-discriminatory (RAND) terms." In addition to meeting these terms, the companies have agreed to make the patents available royalty-free.

 

However, this does not apply for the part of the .NET Framework which is not covered by the ECMA/ISO standard, which includes Windows Forms, ADO.NET, and ASP.NET. Patents that Microsoft holds in these areas may deter non-Microsoft implementations of the full framework.

 

 

 

 

 

 

                                                                 

 

                                           

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