DOTNET

1. What is .NET Framework

           The .NET framework is the Platform for building, deploying and running web services and applications. It provides a highly productive, standards-based, multi-language environment for building such applications. The .NET Framework consists of three main parts: the common language runtime, a hierarchical set of unified class libraries, and a componentized version of Active Server Pages called ASP.NET.

2. Diff Betn ASP and ASP.NET:

3. What u mean by type safety

          Type safe means preventing programs from accessing memory outside the bounds of an object's public properties. Type-safe code accesses only the memory locations it is authorized to access. For example, type-safe code cannot directly read values from another object's private fields or code areas.

          During just-in-time compilation, an optional verification process examines the metadata and intermediate language of a method to verify that they are type-safe. If the code has permission to bypass verification, then this process is skipped. Although verification of type-safety is not mandatory for managed code, type-safety is important for assembly isolation and security enforcement. When code is type- safe, the common language runtime can completely isolate assemblies from each other. This isolation helps ensure that assemblies cannot adversely affect each other and it increases application reliability. Type-safe components can execute safely in the same process even if they are trusted at different levels.

Code that is proven during verification to be type-safe is called verifiably type- safe code. Code can be type-safe, yet not be verifiably type-safe, due to the limitations of the verification process or of the compiler.

When code is not type-safe, unwanted side effects can occur. For example, the runtime cannot prevent unsafe code from calling into native (unmanaged) code and performing malicious operations. When code is type-safe, the runtime's security enforcement mechanism ensures that it does not access native code unless it has permission to do so.

3. Advantages of C#

·         Full support for OOP, including Virtual Functions, and Operator Overloading

·         A consistent and well-defined basic types

·         Inbuilt support for automatic generation of XML documentation

·         Automatic cleanup of dynamically allocated memory

·         Pointers and direct memory access are available but we can use without them in almost all cases.

·         Can be used to write ASP.Net dynamic web pages.

Disadvantages:

• Not extremely powerful when there is looping of around 1000 to 1500 machine cycles.
• Do not clean up the resources the milliseconds they r no longer needed.

surrogates

4. Reflection:

          Because Assemblies are Self-Describing, this opens the theoretical possibility of programmatic access to assembly metadata. There are in fact some base classes that are designed to achieve this. The technology is know as REFLECTION.

5. .NET Base Classes:

          This is an extensive class library that contains pre-written code to perform a huge range of tasks on windows, ranging thru displaying windows and forms, accessing base services, reading and writing to files etc.,

6. Advantage of Stack over Heap:

• Stack or value types can be allocate much more quickly than the heap-allocated types.
• Values of the Stack are instantly and automatically deallocated once they go out of scope.
• Its easy to copy the value of one value type variable into another value type variable.

7. Merge Module:

• A Merge module (.msm) is a single package that contains DLLs, registry entries,  resource files, and setup logic to install the component.
• A merge module allows the creation of reusable set modules.
• When a Windows Installer package is built for the windows application, the merge module can be easily included with this installer package.

8. The components of .Net Framework

• Assemblies: An Assembly is the logical unit that contains compiled code targeted at .Net. An Assembly is completely self-describing, and is also a logical rather than a physical unit however, which means that it can be stored across more than one file. If the assembly is stored across more than one file, then there will be one main file that contains the entry point, and which describes the other files in the assembly.

• Metadata and manifest : An important characteristic of assemblies is that they contain metadata which describes the types and methods defined in the corresponding code. An assembly however also contains the metadata, that describes the assembly itself. This assembly metadata, contained in an area known as “Manifest”, allows checks to be made on the version of the assembly, and on its integrity.

                   THE ADVANTAGE OF METADATA IS THAT APPLICATIONS OR OTHER ASSEMBLIES THAT CALL UP CODE IN A GIVEN ASSEMBLY, DO NOT NEED TO REFER TO THE REGISTRY, OR TO ANY OTHER DATA SOURCE, IN ORDER TO FIND OUT HOW TO USE THAT ASSEMBLY. THIS IS SIGNIFICANT BREAK FROM OLD COM WAY WHERE THE GUID’S OF THE COMPONENTS AND INTERFACES NEED TO OBTAINED FROM THE REGISTRY.

                    EVEN WHEN THE ASSEMBLY ARE SPREAD ACROSS DIFFERENT FILES, THERE IS NO POSSIBILITY FOR OUT OF SYNCHRONIZATION. THIS IS BECAUSE, THE FILE CONTAINING THE ASSEMBLY ENTRY POINT ALSO STORES THE DETAILS OF, AND A HASH OF, THE CONTENTS OF THE OTHER FILES, WHICH MEANS THAT IF ONE OF THE FILES GETS REPLACED, OR IN ANYWAY TAMPERED WITH, THIS WILL ALMOST CERTAINLY BE DETECTED AND THE ASSEMBLY WILL REFUSE TO LOAD.

• Shared Vs Private Assembly:

          Private assemblies are the simplest type. Private assemblies will normally ship with some software, and are intended only to be used with that software.

·         No risk of one s/w package overwriting, modifying, or accidentally loading private assemblies intended for another package.

·         Less need to take security precautions

·         No problem abt name collisions

BECAUSE PRIVATE ARE SELF-CONTAINED, THE PROCESS OF INSTALLING IT IS SIMPLE. THERE ARE NO REGISTRY ENTRIES, AND SO ON TO BE MADE. THIS PROCESS IS KNOWN AS ZERO IMPACT INSTALLATION.

          Shared assemblies are those assemblies that intended to be common libraries that any other application should be able to use. More precautions need to taken against the following risks.

·         Name collisions, involving another company’s shared assembly, implementing types that have the same name as those in our shared assembly.

·         The risk of an assembly being overwritten by a different version.

The solutions to the problems involves placing the shared assembly in a special directory subtree in the file system, that is known as Assembly cache.

In order avoid the risk of name collisions, shared assemblies are given a name that is based on PRIVATE KEY CRYPTOGRAPHY. This name is known as STRONG NAME, Is guaranteed to be unique, and must be quoted by applications that wish to reference a shared assembly.

Problems associated with the risk of overwriting an assembly are addressed by specifying version information in the assembly manifest, and by allowing side-by-side installs.

• Namespaces

                   Namespaces are the way that .NET avoids the name clashes between classes. They are designed, for example, to avoid the situation in which you define a class to represent a customer, and call your class customer, and someone else do the same thing.

     A Namespace is no more than a grouping of datatypes, but it has the effect that the names of all datatypes with in a namespace automatically get prefixed with the name of the namespace. It is also possible to nest the namespace within each other.

     If a namespace is not explicitly supplied, then the type will be added automatically to a nameless global namespace.

• Application domains

        Application domains are designed in such a way of separating the components without resulting in the performance problems associated with passing data between processes. The idea is that any one process is divided in to number of Application domains. Each Application domain roughly corresponds to a single appln, and each thread of execution will be running in particular Application domain.

     If different executables are running in the same process space, then they are clearly able to share the data because theoretically they can see each others data.

Although this is possible in principle, the .NET framework ensures that this does not happen in practice by the technique of inspecting the code for each running appln, to ensure that the code does not stray outside its own data areas. If a running appln specifically does need to communicate or share the data with other appln running in different appln domain, then it must do so by the calling .NET’ remoting services, under the SYSTEM.REMOTING namespace.

      Code that has been verified to check with that it cannot access data outside its appln domain(other than thru explicit remoting mechanism) , it is said to be type safe ( or memory type safe).

• JIT compilers                              

The JIT compiler simply compiles each portion of code as it is called(hence the name just-in-time compiler). When code is compiled once, the resultant native executable is stored until the application exits, so that it does not need to be recompiled the next time that portion of  code is run.

Since the final stage of compilation takes place at runtime, the JIT compiler will know exactly what processor type the program will run on. This means that it can optimize the final executable code to take advantage of any features or particular machine code instructions offered by the particular processor.

9.  Executable Vs Library Assembly:

          The same assembly structure is used for both Executable and Library code. The only real difference is that an executable assembly contains the main program entry point, whereas the library assembly doesn’t.