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Chapter 17. Getting Data from Visio Drawings > Globally Unique Identifiers

Globally Unique Identifiers

Visio utilizes Globally Unique Identifiers in the same manner that Microsoft does: as a mechanism for establishing a total uniqueness for any given object. In this manner, you can establish a reliable correspondence between a specific SmartShape symbol and an external source of data from a database. This is preferable to using sheet identifiers or symbol names.

A Globally Unique Identifier, or GUID, is stored internally as a 128-bit value and is passed as a null-terminated, 39-character string. Be aware that by default all masters have a GUID, but individual SmartShape symbols do not. If a SmartShape symbol or Master SmartShape symbol has a GUID, you may safely assume that no other SmartShape symbol or Master SmartShape symbol in the same Visio document or any other document has the same GUID. Visio generates GUIDs using the same technology that is used to generate OLE 2 GUIDs, and does not reuse them. The chances of generating duplicate GUIDs are remote, even on different systems. It is, however, possible to duplicate a GUID. For example, if you save a Visio drawing file and then make a copy of that file by any usual DOS methodology (copying in Windows Explorer, for example), the SmartShape symbols in that duplicate file are identical to the original file. If you then copy a SmartShape symbol from the copied diagram into the original diagram, you will have two SmartShape symbols with exactly the same GUID. If you copy a Master SmartShape symbol, it will have the same GUID as the original until you edit the Master SmartShape symbol and save the diagram.


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