Object linking and embedding over a computer network

Details Object linking and embedding over a computer network Object linking and embedding over a computer network

1995-02-28

2001-03-13

Courtenay, III, St. John (Department: 2151)

Electrical computers and digital processing systems: multicomput

Computer-to-computer data routing

Least weight routing

Reexamination Certificate

active

06202100

ABSTRACT:

The present invention relates to a method of providing object linking and embedding (OLE) over a computer network, in which an object from a first application at a first computer in the network is incorporated into a second application at a second computer in the network.
A personal computer running a multi-tasking operating system such as OS/2 or Windows
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can support more than one application running simultaneously. It is sometimes necessary for a user to be able to copy data from one application to another, for example to copy numbers from a spreadsheet into a report being prepared on a wordprocessor. One way of performing this transfer is to write the data from the first application into a file on the hard disk, and then retrieve the file into the second application. This is simple but relatively cumbersome.
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OS/2 is a trademark of International Business Machines Corporation and Windows is a trademark of Microsoft Corporation
The OS/2 and Windows operating systems provide a more sophisticated facility, known as the clipboard, for performing such an operation. Applications copy data onto the clipboard (effectively a piece of memory which they then surrender to the operating system). Another application can then interrogate the operating system to find out what is available on the clipboard, and if desired take a copy of the data from the clipboard. Normally an application will write the data into the clipboard in several different formats, and the receiving application will then specify in which of these data formats it would like to receive the data. There are several standard formats, which are available for all applications to use. The clipboard can be used for exchanging text, images, and so on.
One slight complication is that the clipboard supports delayed rendering. In this case, the data itself is not supplied to the clipboard for a particular format, rather only a reference to the data. The data itself is supplied by the originating application only when that particular format is requested by another application. It is possible to use delayed rendering for some, all or none of the formats for any particular piece of data posted to the clipboard.
A typical situation in which a user might employ the clipboard function would be to copy a portion of text from one document to another. The user (generally with a mouse and cursor) would first identify the text to be copied from the first (server) application, and then select the appropriate menu option to place this text in the clipboard. The application would then pass the text to the operating system in a variety of formats—for example, as a text file, as a bit map, as a metafile, as a miniature document complete with format information, and so on. The operating system specifies a list of common predetermined formats, but it is also possible for the application to use its own particular or private format. The formats are normally listed in order of preference, the most preferred format being that which preserves most information from the server about appearance etc (eg ASCII text might be the least preferred format, since it contains no formatting information at all). The user in another (client) application can then request that the text/data is retrieved from the clipboard. Such a request results in the application being asked to select one of the available formats. The application may decide automatically which format to take (perhaps it can only accept a particular format), or it may pass this choice on to the user; typically the most preferred format recognised by the client application would be accepted.
An application can request (via an operating system call) to become the owner or viewer of the clipboard. Becoming the owner is necessary for delayed rendering for the application to receive notification whenever text/data is requested from the clipboard. Becoming a viewer of the clipboard results in the application receiving notification whenever another application writes something to the clipboard.
The clipboard is well-suited to one-off transfers. However, if a particular piece of data in the first application is updated regularly, and each of these updates is to be copied across to the second application, then repeated use of the clipboard becomes tedious and awkward. This problem is addressed by the provision in OS/2 and Windows of an additional function, termed dynamic data exchange (DDE). In DDE a link is set up to copy data from a first application (the server) to a second application (the client). As the name implies the link is dynamic, in that for as long the link is maintained, modifications to the selected entry in the server application are automatically copied to the client application. In other words, the client contains a shadow or mirror of the data in the server.
An application in OS/2 or Windows can initiate DDE by one of two methods. In the first (which in practice is hardly ever used) an application broadcasts an INITIATE message to other applications executing on the node. The message contains the following information: Application Name, Topic, Item, in an ASCII text string, using zeroes as delimiters. The first of these is used to identify the originating application, the topic is then used to specify some particular data file or whatever, whilst the item indicates a position within the data file. For example, a spreadsheet program would give the spreadsheet name as the topic and perhaps use “R1C1” as the item to identify the data cell in the first row and in the first column. Applications receiving the message that wish to participate in DDE with the originating node respond positively, and a DDE conversation can then be set up.
The second method, which has become the de facto standard, is to initiate DDE via the clipboard. When a piece of data is copied to the clipboard, one of the formats used is a private format representative of DDE (under Microsoft Windows conventionally this private format is “Link”). The data stored with this private format is in fact the Application, Topic, and Item parameters described above. When the user retrieves this data into the second (client) application, this private format is indicated as providing DDE. When this option is selected, the client application responds requesting the start of DDE. This response is actually performed by broadcasting a message including the application and topic which is recognised by the originating server, leading to the commencement of the DDE conversation. Note that the conversation actually occurs between two windows, one belonging to the server and one belonging to the client. These are accessed by identifiers known as window handles.
The user can therefore initiate a DDE connection between the server application and the client. At the start of this DDE conversation, the server and client negotiate regarding the data format to use for data transfer between them. Obviously for DDE to work the client and server must be compatible, to the extent that the client recognises the private format placed on the clipboard by the server as an invitation to DDE and they support at least one data format in common.
Another approach to the transfer of data between applications is provided in Microsoft Windows and is termed Object Linking and Embedding (OLE). OLE is somewhat similar to a standard clipboard transfer between applications, except that instead of transferring the data as a bit map, text string or whatever, the data is transferred as an object. In OLE a selected piece of data (an object), is cut from a first application (the source or server) and added to the clipboard in normal fashion. Private formats are used to indicate that Object Linking and/or Object Embedding are available (OLE actually represents two separate facilities); the data associated with these formats specifies the (server) application name and topic and item in the same format used for DDE. In Object Embedding the data is also added to the clipboard in a so-called “native” format, which contains all the information needed to allow the source application

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