All about Assemblies ?

Manifest Based Application

 

This feature provides new support for loading and activating applications through the use of a manifest. Manifest-based activation is essential for supporting ClickOnce applications. Traditionally, applications are activated through a reference to an assembly that contains the application's entry point. For example, clicking an application's .exe file from within the Windows shell causes the shell to load the common language runtime (CLR) and call a well-known entry point within that .exe file's assembly.
The manifest-based activation model uses an application manifest for activation rather than an assembly. A manifest fully describes the application, its dependencies, security requirements, and so forth. The manifest model has several advantages over the assembly-based activation model, especially for Web applications. For example, the manifest contains the security requirements of the application, which enables the user to decide whether to allow the application to execute before downloading the code. The manifest also contains information about the application dependencies.
Manifest-based activation is provided by a set of APIs that allow managed hosts to activate applications and add-ins described by a manifest. These APIs contain a mixture of both new classes and extensions to existing classes.
This activation model also invokes an entity called a Trust Manager that performs the following tasks:
Determines whether an application is allowed to be activated. This decision can be made by prompting the user, querying policy, or by any other means deemed appropriate for a given Trust Manager.
Sets up the security context to run an application in. Most commonly, this step involves setting up a code access security (CAS) policy tree on the application domain in which the application will run.

This activation model also invokes an entity called a Trust Manager that performs the following tasks:

1.    Determines whether an application is allowed to be activated. This decision can be made by prompting the user, querying policy, or by any other means deemed appropriate for a given Trust Manager.

2.    Sets up the security context to run an application in. Most commonly, this step involves setting up a code access security (CAS) policy tree on the application domain in which the application will run.

.NET Framework Developer's Guide

Assembly Manifest

Every assembly,

whether static or dynamic, contains a collection of data that describes how the elements in the assembly relate to each other. The assembly manifest contains this assembly metadata. An assembly manifest contains all the metadata needed to specify the assembly's version requirements and security identity, and all metadata needed to define the scope of the assembly and resolve references to resources and classes. The assembly manifest can be stored in either a PE file (an .exe or .dll) with Microsoft intermediate language (MSIL) code or in a standalone PE file that contains only assembly manifest information.

The following illustration shows the different ways the manifest can be stored.

Types of assemblies

For an assembly with one associated file, the manifest is incorporated into the PE file to form a single-file assembly. You can create a multifile assembly with a standalone manifest file or with the manifest incorporated into one of the PE files in the assembly.

Each assembly's manifest performs the following functions:

  • Enumerates the files that make up the assembly.
  • Governs how references to the assembly's types and resources map to the files that contain their declarations and implementations.
  • Enumerates other assemblies on which the assembly depends.
  • Provides a level of indirection between consumers of the assembly and the assembly's implementation details.
  • Renders the assembly self-describing.
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