We have had a lot of talk about Unique ID’s in the last few weeks and GUID’s have came up a few times. We wanted to add some more information to this topic. GUID’s or Globally Unique Identifier are essentially unique values. These are used by the geodatabase for replication and editing in ArcGIS Mobile in a special field called Global ID. This Global ID field is managed by ArcGIS. When a feature is created, it is auto populated with a GUID, either in ArcGIS Desktop, ArcGIS Server or in ArcGIS Mobile. This should not be used for a Unique ID. These values can change if you have to reload the data at some point or if you drop the Global ID field and re-add it. I would say that you should not use any field managed by something as a unique ID. But there is a GUID Option.
There is also a GUID field type. This allows you to use the GUID data type as a unique ID. It is up to you to manage it, but there are some tools to help. We are looking at adding an option in the Dynamic Value table so the Attribute Assistant that is part of the editing template can add a GUID for you. I have included a VBScript function that can be used in the Field Calculator. Please see the attach GUID.Cal file.
You can read more about GUID’s on this Wiki article. – http://en.wikipedia.org/wiki/Globally_Unique_Identifier