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13-2
Dynamic Data Exchange
● Creating compound documents, such as a word-processing document that
includes a chart produced by a graphics program. Using DDE, the chart will
change when the source data is changed, while the rest of the document remains
the same.
● Performing data queries between applications, such as a spreadsheet querying
a database application for accounts past due.
The following hypothetical example illustrates two co-operating Windows DDE
applications, as seen from the user's point of view:
A Microsoft Excel spreadsheet user wishes to track the price of a particular stock on
the Stock Exchange. The user also has the "Quote" application which gives access to
Stock Exchange data. The DDE conversation between Excel and Quote takes place
as follows:
1. The user initiates the conversation by supplying the name of the application
(Quote) that will supply the data and the particular topic of interest (PRICES).
The resulting DDE conversation is used to request quotes on specific stocks.
2. Excel broadcasts the application and topic names to all DDE applications
currently running in the system. Quote will respond, recognising that the target
application name matches it’s own, establishing a conversation with Excel
relating to the PRICES topic.
3. The user can then request that the spreadsheet be automatically updated when-
ever a particular stock quotation changes by entering a spreadsheet formula in a
cell. For example, the user could request an automatic update whenever a change
in the selling price of EG's stock occurs by specifying the following Excel
formula:
='Quote'|'PRICES'!EG
4. The user can terminate the automatic updating of the EG stock quotation at any
time. Other data links that were established separately will still remain active
under the same PRICES conversation.
5. The user can also terminate the entire conversation between Excel and Quote on
the PRICES topic, so that no specific data links may be subsequently established
on that topic without initiating a new conversation.