OLE Background
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OLE is a mechanism that allows users to create and edit documents containing items or “objects” created by multiple applications.
Note OLE was originally an acronym for Object Linking and Embedding. However, it is now referred to simply as OLE. Parts of OLE not related to linking and embedding are now part of Active technology.
OLE documents, historically called compound documents, seamlessly integrate various types of data, or components. Sound clips, spreadsheets, and bitmaps are typical examples of components found in OLE documents. Supporting OLE in your application allows your users to use OLE documents without worrying about switching between the different applications; OLE does the switching for you.
You use a container application to create compound documents and a server application or component application to create the items within the container document. Any application you write can be a container, a server, or both.
OLE incorporates many different concepts that all work toward the goal of seamless interaction between applications. These areas include the following:
Linking and Embedding
Linking and Embedding are the two methods for storing items created inside an OLE document that were created in another application. For general information on the differences between the two, see the article OLE Background: Linking and Embedding. For more detailed information, see the articles Containers and Servers.
In-Place Activation (Visual Editing)
Activating an embedded item in the context of the container document is called in-place activation or visual editing. The container application’s interface changes to incorporate the features of the component application that created the embedded item. Linked items are never activated in-place because the actual data for the item is contained in a separate file, out of the context of the application containing the link. For more information on in-place activation, see the article Activation.
Note Linking and embedding and in-place activation provide the main features of OLE visual editing.
Automation
Automation allows one application to drive another application. The driving application is known as an automation client or automation controller, and the application being driven is known as an automation server or automation component. For more information on automation, see the articles Automation Clients and Automation Servers.
Note Automation works in both OLE and Active technology contexts. You can automate any object based on COM.
Compound Files
Compound files provide a standard file format that simplifies structured storing of compound documents for OLE applications. Within a compound file, storages have many features of directories and streams have many features of files. This technology is also called structured storage. For more information on compound files, see the article Containers: Compound Files.
Uniform Data Transfer
Uniform Data Transfer (UDT) is a set of interfaces that allow data to be sent and received in a standard fashion, regardless of the actual method chosen to transfer the data. UDT forms the basis for data transfers by drag and drop. UDT now serves as the basis for existing Windows data transfer, such as the Clipboard and dynamic data exchange (DDE). For more information on UDT, see the article Data Objects and Data Sources (OLE).
Drag and Drop
Drag and drop is an easy-to-use, direct-manipulation technique to transfer data between applications, between windows within an application, or even within a single window in an application. The data to be transferred is simply selected and dragged to the desired destination. Drag and drop is based on uniform data transfer. For more information on drag and drop, see the article Drag and Drop.
Component Object Model
The Component Object Model (COM) provides the infrastructure used when OLE objects communicate with each other. The MFC OLE classes simplify COM for the programmer. COM is part of Active technology, as COM objects underlie both OLE and Active technology. For more information about COM, see the OLE Programmer’s Reference and the (ATL) Reference.
Some of the more important OLE topics are covered in the following articles:
For information about handling context-sensitive Help in OLE applications, see the article Help: OLE Support for Help.
For general OLE information not found in the above articles, see the OLE Programmer’s Reference. Another good source of information is Kraig Brockschmidt’s book Inside OLE (Microsoft Press, 1995, second edition).