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

r_wendler@harvard.edu

Baker Library, Harvard Business School, Historical CollectionsTC6512.0001:6512