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Keeping the pieces together: The Role of METS in the Preservation of Digital Content
Robin WendlerHarvard University LibraryJanuary 16, 2005
[Men in crate looking up, photograph, ca. 1905. Harvard University Archives HUK 363 p (Fig. 8) ]
Standards everywhere, but nothing there for me…
• As of 2000– A plethora of descriptive metadata standards– Emerging standards for digital conversion, BUT– No open standard for representing a digital object
• Display and navigation• Archiving• Exchange / Transport
– Digital repositories managing files, not objects
OAIS Functional Entities
OAIS Information Model
METS to the rescue
• Metadata Encoding and Transmission Standard– An XML schema for encoding descriptive,
administrative, and structural metadata about a digital object
– http://www.loc.gov/standards/mets/
– An initiative of the Digital Library Federation– Development: METS Editorial Board– Principle author: Jerome McDonough, NYU– Website maintained by: Library of Congress
METS Basics
• METS provides a framework for– Content files– Metadata– Relationships
• Suitable for – Open Archival Information Systems
• Archival information package (AIP)• Submission information package (SIP)• Dissemination information package (DIP)
– Display and navigation of digital objects– Sharing of digital objects among libraries and archives
Structure of a METS File
METS
metsHdr
structMap
admSec
dmdSec
fileSec
structLink
behaviorSec*
Inventory or manifest of component files
Header describing METS file itself
Descriptive metadata
Administrative metadata: -- technical, source, rights, provenance
Structure map: the heart of METS
Structural map linking, i.e., hyperlinks
Executable behaviors
* Not commonly used
Structure Map
Title pagePreface page i page iiChapter 1 page 1 page 2…
<div LABEL=“Title page”><div LABEL=“title page” ORDER=“1” TYPE= <fptr FILEID=“A”></div>
<div LABEL=“Preface”><div LABEL= “page i” ORDER=“2” ORDERLABEL=“i”> <fptr FILEID=“B”></div><div LABEL= “page ii” ORDER=“3”> <fptr> FILEID=“C”></div>
<div LABEL=“Chapter 1”><div LABEL=“page 1” ORDER=“4”> <fptr FILEID=“D”></div><div LABEL=“page 2” ORDER=“5”> <fptr FILEID=“E”>…
Referring to Metadata
METS
metsHdr
structMap
admSec
dmdSec
fileSec
structLink
behaviorSec
METS does not define descriptive or administrative metadata elements. dmdSec and admSec are buckets or sockets where externally-defined metadata can be supplied or referenced
Three techniques:
• In-line XML• Wrapped base-64 encoded data• Pointers to external information (e.g., URNs, handles)
METS Board endorses range of recommended “extension schemas”
Book Chapter 1 page 1 page 2…
<div LABEL=“Reports of the president and treasurer” DMDID=“D1”> <div LABEL=“Chapter 1” DMDID=“CH1”>
<div LABEL=“page 1” ORDER=“3”><fptr FILEID=“D” >
<div LABEL=“page 2” ORDER=“4”><fptr FILEID=“E”>…
<dmdSec ID=“D1” ><mdWrap MDTYPE="MODS"> <xmlData> <mods:mods xmlns:mods="http://www.loc.gov/mods/v3" xsi:schemaLocation=http://www.loc.gov/mods/v3 …> <mods:name> <mods:displayForm> Radcliffe College</mods:displayForm> </mods:name> <mods:titleInfo> <mods:title> Reports of the president and treasurer for...</mods:title> </mods:titleInfo> </mods:mods> </xmlData> </mdWrap> <mdRef LOCTYPE=“URL” MDTYPE=“MARC” xlink:href=http://... BNI3165”/>
Use of MODS Extension Schema for Descriptive Metadata
Catalog record
Catalog record
Referring to Content Files
METS
metsHdr
structMap
admSec
dmdSec
fileSec
structLink
behaviorSec
Digital Content can exist inside or outside a METS file.
Three techniques:
• In-line XML• Wrapped base-64 encoded data• Pointers to external information (e.g., URNs, handles)
Structure Map
Chapter 1 page 1 page 2…
<div LABEL=“Chapter 1”><div LABEL=“page 1” ORDER=“3”>
<fptr FILEID=“D” ><div LABEL=“page 2” ORDER=“4”>
<fptr FILEID=“E”>…
<fileSec> <fileGrp> <file ID=“D" ADMID=“TMD01” MIMETYPE="image/jpg“>
<FLocat LOCTYPE="URL" xlink:href="http://nrs.harvard.edu..." />
</file>
<amdSec> <techMD ID=“TMD01”> <mdWrap MDTYPE="NISOIMG" LABEL="Service Copy Technical Metadata"> <xmlData> <mix:mix> <mix:BasicImageParameters> <mix:Format> <mix:MIMEType>image/jpg</mix:MIMEType> <mix:ByteOrder>big-endian</mix:ByteOrder>
<…
Use of MIX Extension Schema for Image Technical Metadata
Profiles
• Challenge: – METS is very flexible– Flexibility allows variant practices– Variant practices undermine interoperability
• Response:– Create profiles: documented ways of using METS
• Profiles constrain practice (this is a good thing)
• Specify required structures, extension schemas, vocabularies, etc.
– Communities of interest develop and register shared profiles – XML schema for METS profiles
• Human-readable, not machine-actionable
Adoption
• Library of Congress• California Digital Library• Harvard University Library• Oxford University• MIT/DSpace• National Library of Wales• Stanford University Library• Indiana University Library• University of California,
Berkeley
• University of Chicago Library• University of Graz, Austria• Florida Center for Library
Automation• Göttingen State and University
Library• OCLC Digital Archive• RLG Cultural Materials• Philadelphia Museum of Art• University of Alberta• … among others
Used By:
Benefits
• Modeling the whole object, not just files
Open standard+ XML encoding + Growing base of tools----------------------------------= Manageable, sharable, preservable digital
objects
Thank You!
Robin Wendler
Baker Library, Harvard Business School, Historical CollectionsTC6512.0001:6512