Question about descriptive metadata and PCDM

[Michael Bolton]

Hello all,

Andrew suggested I ask my question in this forum.  I hope I'm in the right place.

I have been reading about the Portland Common Data Model and Fedora 4 and now have a sandbox where I am trying it out.  I read the *LDP-PCDM-F4 in Action*  page in the wiki and noted a remark about where descriptive metadata should and should not be stored.  In particular, I saw a comment that descriptive metadata should not be in DirectContainers.  Before I get too far down this path, is there a best practice on where I should store technical and descriptive metadata for photos and images?  I am looking to create an image collection in F4 and use it in several applications and I would like to enter metadata once.

Thanks

_____________________________________________________________________

Michael W. Bolton  |  Assistant Dean, Digital Initiatives

Sterling C. Evans Library  |  Texas A&M University

5000 TAMU  |  College Station, TX  77843-5000

Ph: 979-845-5751  |  Michael...@tamu.edu

http://library.tamu.edu

[Esmé Cowles]

Michael-

Yes, you're absolutely in the right place.

For the technical metadata, you can add it to the binary description attached to each file. You might want to use properties form EBUCore[1] or EXIF[2] for that. If you have XML or other metadata files with technical metadata, you could add them as files and link them to the binary they describe with iana:describes (<http://www.iana.org/assignments/relation/describes>).

For descriptive metadata, you can attach properties to your PCDM Objects using, e.g., Dublin Core[3], or any number of ontologies.

So you might wind up with something like (omitting the LDP triples for brevity):

<http://localhost:8080/rest/obj1> a pcdm:Object ;
pcdm:hasFile <http://localhost:8080/rest/obj1/files/file1> ;
dc:title "Title Here" .

<http://localhost:8080/rest/obj1/files/file1> a pcdm:File ;
ebucore:height "3024" ;
ebucore:width "4032" .

Of course there are many, many more ontologies and controlled vocabularies you might want to use, depending on what your use cases and what your metadata looks like. But I hope this is helpful.

-Esmé

1. http://www.ebu.ch/metadata/ontologies/ebucore/ebucore#
2. http://www.w3.org/2003/12/exif/ns#
3. http://dublincore.org/documents/dcmi-terms/

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[Daniel Lamb]

Hi Michael,

PCDM prescribes descriptive metadata to be on pcdm:Objects and technical metadata for binaries be on pcdm:Files.  There's no restrictions based on LDP constructs.  So you can put your descriptive metadata on any type of container so long as it has an rdf:type of pcdm:Object.

HTH

~Danny

[Michael Bolton]

Outstanding.  Thanks for the replies.  And I am still learning my terminology.

Esmé,

I appreciate the information on the ontologies.  I have been working with EXIF and XMP (IPTC-core) in Paintshop and Photoshop and I wanted to add that metadata to the image files.  

And as Daniel pointed out, it makes perfect sense the technical metadata (EXIF data) would be at the file level.  I added that by updating the object

    .../fcrepo/rest/mwbObjects/Photos/Images/photo2/files/image_0002.jpg/fcr:metadata

I hope that was the right place.  It worked and shows up when I display that object.

In my model from above, 

• "photo2" is a ldp:Container (pcdm:Objects) 
• "files" is a ldp:DirectContainer (pcdm:Objects)  that contains "image_0002.jpg"
• and I added the technical metadata to the JPG by appending the "/fcr:metadata"
  

So, I gather my descriptive metadata would best be added to the "photo2" object.  I hope I am not being dense here but I think I am close to understanding this.

Again, thanks for the comments.   They really help.

[Esmé Cowles]

Michael-

Yes, that all sounds correct to me — since photo2 is a pcdm:Object, that's the place to attach descriptive metadata properties.

-Esmé

[Michael Bolton]

Esmé,

I would like to go back to something you said earlier, that is, if I have an XML file I can link that to the JPG via an iana:describes.  That sounds interesting.  I would add the file to the same container as the binary and then add the RDF that would link the two files.  In that case, I would need to read and process two objects to get the binary and all the metadata. And of course I could still add metadata to the file just as I am doing now.

Thank you for your help.  I think I am ready to start building my collection.

[Andrew Woods]

Hello Esmé,

Thanks for your recommendations here.

I was looking into the iana:describes / iana:describedby pattern for associating other repository resources as you detailed, and as mentioned in the PCDM wiki:
https://github.com/duraspace/pcdm/wiki/Related-Files

Do you happen to be aware of a workaround for the fact that those two predicates (describes/describedby) are "server managed" and prohibited to update in Fedora:

- https://github.com/fcrepo4/fcrepo4/blob/master/fcrepo-kernel-api/src/main/java/org/fcrepo/kernel/api/RdfLexicon.java#L194-L200
- https://github.com/fcrepo4/fcrepo4/blob/master/fcrepo-kernel-api/src/main/java/org/fcrepo/kernel/api/RdfLexicon.java#L242

If not, it seems like we may want to lift that restriction for these predicates.

Thoughts?

Andrew