>From Visual Studio Help.....
GUID (pronounced goo-id) stands for Globally Unique IDentifier, a 128-bit
(16-byte) number generated by an algorithm designed to ensure its
uniqueness. This algorithm is part of the Open Software Foundation (OSF)
Distributed Computing Environment (DCE), a set of standards for distributed
computing.
GUIDs are used to uniquely identify entries in the Windows registry. For
example, Visual Basic automatically generates a GUID that identifies your
type library in the Windows registry.
Visual Basic also automatically generates a GUID for each public class and
interface in your component. These are usually referred to as class IDs
(CLSID) and interface IDs (IID). Class IDs and interface IDs are the keys to
version compatibility for components authored using Visual Basic.
Note You may also see GUIDs referred to as UUIDs, or Universally Unique
IDentifiers.
What If Visual Basic Runs Out of GUIDs?
This is not a problem we need to worry about in our lifetimes. The algorithm
that generates GUIDs would allow you to compile several new versions of your
component every second for centuries - without repeating or colliding with
GUIDs generated by other developers.
----- Original Message -----
From: "Stephen R. Hartmann" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Monday, April 23, 2001 11:21 PM
Subject: RE: Random numbers continued
> I think I can give you a reason for random numbers versus autonumbers. I
> was once asked to look into interfacing with a very sophisticated contact
> management system. This system used no autonumbers. It used something it
> called a GUID. I forget what the GUID stood for, but they were very large
> random numbers. The reason for the GUIDs in this application was
> replication. The system was built to support offline processing. Whent
the
> user came back on line and merged their changes, the randomness of the
IDs,
> made the merging process much easier. The developer I talked to said the
> odds of duplicating one of these very large numbers were extremely low.
>
> There is a minore performance reason for using random numbers. The way
> indexes are built, if your ID is indexed, the performance of your indexes
> will degrade as new records are added with the values scewed towards the
> same range of numbers.
>
> Steve
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
> Behalf Of Bob Powell
> Sent: Monday, April 23, 2001 4:26 PM
> To: [EMAIL PROTECTED]
> Subject: Random numbers continued
>
>
>
> Ladies and Gentlemen:
>
> I see I have instigated a large discussion on
> random numbers. Let me explain where this is coming from.
>
> I have a DBA that feels id numbers which link the
> various database files together should be random in nature.
> I explained that R:base has its own way of
> automatically generating consecutive numbers which
> guarantees uniqueness. I also feel that allowing R:BASE to
> generate the number automatically in the table is better
> than having to write application code to do it. As we all
> know this is a must and R:Base's solution is just fine with
> me.
>
> She feels however that random generating a
> unique id number is a better way to go although I am hard
> pressed to have her explain to me why. So I just wanted to
> know if someone had done something I have never been able
> to do.
>
> Having taken PASCAL 100 years ago I agree with the
> idea that a random generator will eventaually repeat a
> number. I was taught that a random generator should in
> fact repeat the same sequence if the same seed is used.
> Somethimes for testing being able to generate the same
> random sequence is good. At other times it is not, but it
> seems to me that as long as you change the seed the random
> sequence should be different which I think is what you all
> have discovered. This seems perfectly acceptable to me if
> I remeber my training years ago.
>
> Based on the way I understand random generators in all
> languages R:BASE's is responding correctly. I think what
> we all are discovering is that there is not way to randomly
> generate unique numbers. This is OK with me since I feel
> the unique consective numbering allowed in tables works
> just dandy.
>
> Maybe I need to explain to her that sometimes database
> theory needs to be over-riden by practicality. She has it
> in her notes from one of her database instructors that
> random generated id numbers is a good thing.
>
> ----------------------
> Bob Powell
> The Hotchkiss School
> Lakeville, Connecticut
> Systems Administrator
> [EMAIL PROTECTED]
>
>
