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 in the namespaces 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 versions up to and including 2.0 can be installed on most older versions. The current version is 3.0, which was released in November 2006, and is supported on Windows XP Service Pack 2, Windows Server 2003 Service Pack 1, and Windows Vista.

Significance

For software developers, the .NET Framework is one of the most significant changes to the Windows platform since its introduction. 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 offers 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 success. Its popularity positioned it as a competitive threat to Microsoft. After failed attempts (due to copyright issues) 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 code that is 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 and deployment of Windows applications has been the bane of many developers' existence. Registry settings, file distribution and DLL hell have been nearly completely eliminated by new deployment mechanisms in the .NET Framework.
• 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 not widely used.

.NET Framework architecture

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, 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 types 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.

Versions

Microsoft started development on the .NET Framework back in the late 90s originally under the name of Next Generation Windows Services (NGWS). By late 2000 the first beta versions of .NET 1.0 were being released.

.NET Framework 1.1

This is the first major .NET Framework upgrade. It is available on its own as a redistributable package or in a software development kit. It is also part of the second release of Microsoft Visual Studio .NET (released as Visual Studio .NET 2003). This is the first version of the .NET Framework to be included as part of the Windows operating system - it is part of Windows Server 2003. Windows Server 2003 originally shipped with the 1.1 RTM version.

Changes since 1.0

• Built-in support for mobile ASP.NET controls. Previously available as an add-on for .NET Framework, now part of the framework.
• Security changes - enable Windows Forms assemblies to execute in a semi-trusted manner from the Internet, and enable Code Access Security in ASP.NET applications.
• Built-in support for ODBC and Oracle databases. Previously available as an add-on for .NET Framework 1.0, now part of the framework.
• .NET Compact Framework - a version of the .NET Framework for small devices.
• Internet Protocol version 6 (IPv6) support.
• Numerous API changes. For a detailed list, see GotDotNet: API Changes between versions of the .NET Framework.

.NET Framework 2.0

Released with Visual Studio .NET 2005, Microsoft SQL Server 2005 and BizTalk 2006.

• The 2.0 Redistributable Package can be downloaded for free from Microsoft.
• The 2.0 Software Development Kit (SDK) can be downloaded for free from Microsoft.
• It is included as part of Visual Studio 2005 and Microsoft SQL Server 2005.
• Version 2.0 is the last version with support for Windows 2000

Changes since 1.1

• Numerous API changes. For a detailed list, see GotDotNet: API Changes between versions of the .NET Framework.
• A new hosting API for native applications wishing to host an instance of the .NET runtime. The new API gives a fine grain control on the behavior of the runtime with regards to multithreading, memory allocation, assembly loading and more (detailed reference). It was initially developed to efficiently host the runtime in Microsoft SQL Server, which implements its own scheduler and memory manager.
• Full 64-bit support for both the x64 and the IA64 hardware platforms.
• Language support for Generics built directly into the .NET CLR.
• Many additional and improved ASP.NET web controls.
• New data controls with declarative data binding.
• New personalization features for ASP.NET, such as support for themes, skins and webparts.
• .NET Micro Framework - a version of the .NET Framework related to the Smart Personal Objects Technology initiative more....

.NET Framework 3.0

.NET Framework 3.0, formerly called WinFX^[1], includes a new set of managed code APIs that are an integral part of the upcoming Windows Vista and Windows Server "Longhorn" operating systems. It is also available for Windows XP SP2 and Windows Server 2003 as a download. There are no major architectural changes included with this release; .NET Framework 3.0 includes version 2.0 of the Common Language Runtime.

.NET Framework 3.0 consists of four major new components:

• Windows Presentation Foundation (WPF), formerly code-named Avalon; a new user interface subsystem and API based on XML and vector graphics, which will make use of 3D computer graphics hardware and Direct3D technologies.
• Windows Communication Foundation (WCF), formerly code-named Indigo; a service-oriented messaging system which allows programs to interoperate locally or remotely similar to web services.
• Windows Workflow Foundation (WWF) allows for building of task automation and integrated transactions using workflows.
• Windows CardSpace (WCS), formerly code-named InfoCard; a software component which securely stores a person's digital identities and provides a unified interface for choosing the identity for a particular transaction, such as logging in to a website.

.NET Framework 3.5

Template:Future software In an interview with Channel 9, Jason Zander, general manager of the .NET Framework team at Microsoft, discussed the version of the framework that will follow version 3.0.^[2] Tentatively titled "version 3.5", this version will include a new compiler that will support new features such as Language Integrated Query, as well as new language features in C# and VB.NET. This version of the framework is slated to be included with the version of Visual Studio following the 2005 release (Codenamed Orcas).

.NET vs. Java and the J2EE

The CLR and C# have many similarities to Sun's JVM and Java. They are strong competitors. Both are based on a virtual machine model that hides the details of the computer hardware on which their programs run. Both use their own intermediate byte-code, Microsoft calling theirs Microsoft Intermediate Language (MSIL) and Sun Java bytecode. On .NET, the byte-code is always JIT-compiled: with Java, the byte-code can be either interpreted or JIT-compiled. Both provide extensive class libraries that address many common programming requirements, and both address many security issues that are present in other approaches. The namespaces provided in the .Net Framework closely resemble the platform packages in Java EE API Specification both in style and invocation.

.NET in its complete form (Microsoft's implementation) is currently only fully available on Windows platforms, whereas Java is fully available on many platforms. .NET was built from the ground-up to support multiple programming languages while targeting Microsoft Windows, while the Java platform was initially built to support only the Java language on many operating system platforms under the slogan, "Write once, run anywhere."

Microsoft's reference implementation of .NET is closed source, whereas Sun's reference implementation of Java is becoming GPL (including the class library, the compiler, the Virtual machine, and the various tools associated with the Java Platform).

On the other hand, the Mono project, an open source implementation of subsets of the .NET Framework including the Common Language Runtime for the Linux, Solaris, Mac OS, and Windows platforms, has been in production for some time. Meanwhile, the Java Virtual Machine environment is host to many alternative languages not supported by Sun.

For a more detailed examination of the similarities and differences between the two, see a comparison of Java and C#.

Criticism

Some concerns and criticisms relating to the .NET Framework include:

• The introduction of the .NET Framework has resulted in many changes to Microsoft development tools and languages. Some of these changes are controversial, especially for developers transitioning from an earlier version of a Microsoft product.^[3] Additionally, there were numerous backward incompatibilities between .NET 1.0, .NET 1.1, and .NET 2.0 ^{[4] [5]}.
• Applications running in a managed environment such as the Microsoft framework's CLR or Java's JVM tend to require more system resources than functionally similar applications that access machine resources more directly. However, some applications have been shown to perform better in .NET than in their native version. This could be due to the use of relatively well-performing functions in the .NET framework, JITting of managed code, or other aspects of the CLR. ^{[6] [7]}

• Although it is more a business decision than a real criticism on the framework, some people have expressed concern that the framework is too much tied on the Microsoft Windows operating system (see for example Bjarne Stroustrup's homepage). However, the existence of the alternative implementations for other platforms (although not complete yet) would seem to alleviate this criticism.

• There is also concern in the development community about the fact that a .NET assembly, as produced by the .NET programming environments, can be reverse-engineered to reveal some of the programming techniques and algorithms used by an application. While this kind of reverse-engineering is possible with all programs, those that compile to byte-code, as .NET and Java do, are somewhat more vulnerable. Reverse engineering can lead to the loss of valuable intellectual property and the bypassing of licence control mechanisms. Some developers are using obfuscation and other techniques in an attempt to protect their intellectual property and license revenues. Indeed Microsoft includes a tool called the "dotfuscator community edition" - a product of PreEmptive Solutions, in the full version of Visual Studio 2005.

Alternative implementations

The Microsoft .NET Framework is the predominant implementation of .NET technologies. Other implementations for parts of the framework exist. Since the runtime engine is described by a ECMA/ISO specification, other implementations of it are unencumbered by copyright issues. It is more difficult to develop alternatives to the base class library (BCL), which is not described by an open standard, and may be subject to copyright restrictions. Additionally, parts of the BCL have Windows-specific functionality and behavior, so implementation on non-Windows platforms can be problematic.

Some alternative implementations of parts of the framework are listed here.

• Microsoft's Shared Source Common Language Infrastructure is a shared source implementation of the CLR component of the .NET Framework. It runs on Microsoft Windows XP, FreeBSD, and Mac OS X 10.2.
• Portable.NET (part of DotGNU) provides an implementation of the Common Language Infrastructure (CLI), portions of the .NET Base Class Library (BCL), and a C# compiler. It supports a variety of CPUs and operating systems.
• Mono is an implementation of the CLI and portions of the .NET Base Class Library (BCL), and provides additional functionality. It is dual-licensed under free software and proprietary software licenses. Mono is being developed by Novell, Inc. It includes support for ASP.NET, ADO.NET, and evolving support for Windows Forms libraries. It also includes a C# compiler, and a VB.NET compiler is in pre-beta form.

See also

• .NET Remoting
• ADO.NET
• ASP.NET
• Microsoft .NET Languages
• Platform Invocation Services (P/Invoke)
• Microsoft Enterprise Library
• Microsoft Intermediate Language
• POCO
• Microsoft Foundation Class Library
• Mono (software)

References

External links

Microsoft

• ".NET Framework Developer Center". Microsoft Developer Network. Retrieved 2006-11-21.
• "Windows Vista". Microsoft Developer Network. Retrieved 2006-11-21.
• "GotDotNet". Microsoft Developer Network. Retrieved 2006-11-21.

Other

• DotNetSpace ASP.NET 2.0 Articles and Code Examples
• The Code Project - Visual Studio and .NET Articles
• INETA - promotes use of .NET technologies
• .Net Framework 3.0 section on NetFXGuide.com
• BCLTeam's WebLog
• DotNetKicks.com A community driven source of .NET news and links