Windows Management Instrumentation (WMI) - An Introduction
Instrumentation (WMI) is a component of the Windows Operating System that
is used to get information about your computer system or network. Using
Windows Management Instrumentation it is possible to create applications
that interact with your system and get the required information about
The programming interfaces provided by WMI are not limited to VBScript, C++, ODBC, Visual Basic and HTML. WMI is very useful for system administrator since they can use Windows Management Instrumentation to automate most of the administrative tasks that they need to accomplish. Windows Management Instrumentation can integrate with components to make the tasks much easier.
The application that is developed to retrieve information about the system will interact with the WMI layer to get information. It is not necessary for the applications to interact with the operating systems APIs since the APIs cannot retrieve all the required information. There are limitations of the operating systems APIs which are overcome by the WMI. As said earlier that application that is created to get system information can be created using a variety of languages to interact with the WMI such as Visual Basic, C++, and Active X. The data that is retrieved by the WMI is stored using a model called Common Information Model (CIM) which is a standard for storing information.
CIM is an extensible, object oriented model which is used to store information about the computer system. CIM can be used to create classes through the use of WMI to represent different part of the computer system such as the hard drives, routers, applications and other user defined components in the network. It is easy to create an instance of a hard drive using the CIM classes and make any changes to the instance which will be reflected in the hard drive.
CIM is a language independent programming model. Associations and Schemas are used in CIM model to relate different parts of the system and to create different management environments. Object oriented techniques are used to represent the different parts of the system such as the physical and the logical drives in a computer system.
As we know the class can have properties and methods, the CIM model also uses the properties and methods to describe the data and the behavior of the different parts of the computer system or network. CIM is a language and platform independent model. The Windows Management Instrumentation includes and extension to CIM that describes the different Windows platforms.
The CIM has three different levels of classes called the Core, Common and the Extended classes. The core classes represent all the areas of the management whereas the Common classes represent the objects of specific areas which are the extensions of the core classes. The extended classes as the name specifies are the extensions to the common classes and they represent specific technologies and apply to specific platforms such as Unix or Windows environments.
As we have said earlier, Windows Management Instrumentation supports the concepts of schemas. When we say schema, it is a group of classes that describes a particular environment. Windows Management Instrumentation platform SDK uses two schemas called the CIM and the Win32 schema. The schemas that start with CIM_ are CIM schemas and the schemas that start with Win32_ are Win32 schemas.
The core classes and the common classes of the Common Information Model are found in the CIM_ schema and the windows environment specific extended classes are found in the Win32_ schema. It is possible to create your own schema for any specific environment. You can create classes that describe the environment you want and add them to the schema. But mostly the CIM and the Win32 schemas are inherited for most of the requirements.
The Managed Object Format (MOF) language is used to create new CIM class. This is the most common method of creating new CIM classes. Almost all the programming languages of Microsoft are supported with methods to create and manipulate CIM classes. A simple text editor can be used to describe new CIM classes using the MOF. You can develop your own set of classes to describe an application that you want to create.
An MOF compiler is used to compile the MOF file that is created in a text editor and creates the CIM classes and adds them to the WMI repository. These CIM classes that are created by you can be used by any administrator to perform the required task. Operating systems like Windows 2000, Windows ME, and Windows XP have MOF compiler as a part of the installation in the Windows Management Instrumentation core.
The Managed Object Format language is used for describing the CIM classes. It is totally different from the conventional languages such as C++ and other APIs. It is very easy, human-readable, and reusable. It reduces the development time required since the no of lines of code that are written are drastically reduced by MOF language. Since this language is very easy to read it will be easy to make any modifications in the future which will reduce the cost of employing a person to make the changes.
The MOF file that is created can be shared by another application. Hence an MOF file that is created for a particular environment can be reused by another application and hence it reduces the cost of rewriting the MOF file again. With MOF you can create a class, instance of the class, methods and also insert MOF code in to WMI.
Scripting API for WMI can be used to develop quick applications to manage the environment. Windows Script Host (WSH) scripts can access all the WMI classes for a computer system. It is easy to create an application using scripts. Active Directory objects can also be accessed using the ADSI scripts. Using scripting you can do all the tasks that can be done using programming languages such as C++ and C. Many simple examples are provided in the MSDN website on the topic Scripting in WMI, which can be used to start writing applications using Windows Management Instrumentation.
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