What is a Document ID?

G
Posted By
Gener
Feb 24, 2004
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421
Replies
8
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Closed
I’ve not found much on this in my User Guide and some searches, so maybe it’s best to ask here.

In Photoshop CS, File > file info > advanced and under "XMP Media Mangement properties" is a serial number that gets tagged to any file I open. It starts as "adobe:docid:photoshop: <really long serial number>"

So what is the purpose of this document id?
Can it only be read or displayed by software other than Adobe products? Is this a simple serial number or is it decoded to offer up other information?

Gene
G
Gener
Feb 24, 2004
Thanks Len:

I’m poking around there. An XMP primer looks like a good start.

Gene
PD
Paul_D._Ferguson
Feb 24, 2004
The documentID serves as a unique identifier for the file. It is part of XMP’s media management schema, which is primarily used by document asset management (DAM) systems.

Since XMP data can be stored separately from its file (for example, as a sidecar XML file, or in a DAM system’s database) the documentID is used to insure that XMP data refers to the correct file. Just keeping track of the file’s name won’t work for this purpose, as the original file might have been renamed, or other files might have the same name. Due to the way docID’s are generated, the chances of two files having the same docID is exceedingly remote.

DocID’s are generated when a file (or more precisely, its metadata) is first created, and remain unchanged even if the file is modified; in contrast, the instanceID changes each time the file is modified, which allows you to determine when XMP data may be out of sync with its file. The docID number itself doesn’t contain any intrinsic information, so don’t spend time trying to decode it.

XMP and the media management schema are publicly documented, so other applications can be read or display the docID if they are XMP-savvy. For more information, refer to the XMP specification: < http://partners.adobe.com/asn/developer/xmp/pdf/xmpspecifica tion.pdf>. There’s also a section of the Adobe User to User forum devoted to all things XMP.

Hope this helps,

Paul
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Gener
Feb 25, 2004
Thank you, Paul. It helps very much, saved me from rooting around…and has put the question to rest. I’ve downloaded the pdf and will look it over.

Much appreciated,

Gene
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YrbkMgr
Feb 25, 2004
Is the DocID only for PSDs or is it preserved throughout file format changes, such as JPG or PDF?
PD
Paul_D._Ferguson
Feb 25, 2004
The doc ID is present in all formats that support XMP, which includes PSD, TIFF, PDF, JPEG and others (more information can be found in chapter 5 of the XMP spec mentioned in my previous post).

The docID is not preserved through file format changes or "save as" operations, since those both create new documents. A new docID is generated and replaces the existing one.

Paul
Y
YrbkMgr
Feb 25, 2004
Very interesting. Thank you Paul. I’m wondering about the variation in application of such a spec. This is a bit naive, but I’m wondering if one might be able to trace or prove copyright, specifically on the web using DocID.

Not that there aren’t better means (although I don’t claim to be an expert in the area), I’m just thinking of different applications of DocID.

<star trek computer voice> working… </star trek computer voice>
G
Gener
Feb 25, 2004
I played around with renaming files, saving for web, and saving to another format. In those cases a new document id was given, but there was a note which document id it was derived from.

If I changed a psd file as a jpeg in an application outside of PS CS, for instance ACDSee 5, then re-opening that jpeg in PS CS showed a new document id with no trace of where it came from.

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