How are Global ID numbers created?

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05-02-2021 11:18 AM
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Tim_Callahan
New Contributor II

I was wondering how these numbers are assigned, why they are look like Windows registry numbers, and what their scope is. Are they global only within the database they're created in? The documentation I've been able to find is vague on this.

 

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Luke_Pinner
MVP Regular Contributor

They are a UUID (Universal Unique Identifier):

GlobalID
  1. [ESRI software] A field of type UUID (Universal Unique Identifier) in which values are automatically assigned by the geodatabase when a row is created.


Universally unique identifier (UUID):

A universally unique identifier (UUID) is a 128-bit number used to identify information in computer systems. The term globally unique identifier (GUID) is also used, often in software created by Microsoft.

When generated according to the standard methods, UUIDs are, for practical purposes, unique. Their uniqueness does not depend on a central registration authority or coordination between the parties generating them, unlike most other numbering schemes. While the probability that a UUID will be duplicated is not zero, it is close enough to zero to be negligible.

They look like windows registry numbers, because Microsoft uses UUIDs (they call them GUIDs).

 

 

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DavidPike
MVP Frequent Contributor

My understanding is that they are generated with a random bit function or similar.  Not sure what you mean by their scope, they're just randomly generated unique IDs which are extreeeemely unlikely to be repeated due to their bit size.

Tim_Callahan
New Contributor II

Sorry, I should have been more precise. By scope, I meant what is the level at which they are guaranteed to be unique? Within a database, for sure. But I've seen references in the documentation say that they are global between databases as well, which confused me. I'm not sure how that would work.

DanPatterson
MVP Honored Contributor

Is this the vague documentation to which you refer?

ArcGIS field data types—ArcGIS Pro | Documentation


... sort of retired...
Tim_Callahan
New Contributor II

Yes it is. That's the reference to across multiple databases I was referring to. This may just be my comprehension problem, but I found it confusing trying to understand how they get assigned if they work across more than one database.

That and why they are in registry format.

Luke_Pinner
MVP Regular Contributor

They are a UUID (Universal Unique Identifier):

GlobalID
  1. [ESRI software] A field of type UUID (Universal Unique Identifier) in which values are automatically assigned by the geodatabase when a row is created.


Universally unique identifier (UUID):

A universally unique identifier (UUID) is a 128-bit number used to identify information in computer systems. The term globally unique identifier (GUID) is also used, often in software created by Microsoft.

When generated according to the standard methods, UUIDs are, for practical purposes, unique. Their uniqueness does not depend on a central registration authority or coordination between the parties generating them, unlike most other numbering schemes. While the probability that a UUID will be duplicated is not zero, it is close enough to zero to be negligible.

They look like windows registry numbers, because Microsoft uses UUIDs (they call them GUIDs).

 

 

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DavidPike
MVP Frequent Contributor

I think it's best to conceptualize the cause of their uniqueness across databases etc. is best seen as relying on the huge statistical unlikelihood of any UIDs being repeated rather some kind-of a cross-database intervention to ensure uniqueness.

As to the format, no idea.