Don Sawyer /NASA/NSSDC ISO “Reference Model For an Open Archival Information System (OAIS)” Tutorial Presentation Lou Reich /CSC Don Sawyer /NASA/NSSDC May 2000 1

Outline of Talk History Reference Model overview Digital Archive Directions (DADs) workshop AWIICS workshop Reference Model Status

NASA Role National Space Science Data Center NASA’s first digital archive Experienced many technology changes since 1966 Consultative Committee for Space Data Systems International group of space agencies Developed variety of science discipline- independent standards Became working body for an ISO TC 20/ SC 13 about 1990 TC20: Aircraft and Space Vehicles SC13: Space Data and Information Transfer Systems

Initial Archive Standards Proposal ISO suggested that SC 13 should develop archive standards Address data used in conjunction with space missions Address intermediate and indefinite long term storage of digital data

Response Response to Consultative Committee for Space Data Systems (CCSDS) and ISO TC 20/SC 13 No framework widely recognized for developing specific digital archive standards Begin by developing a ‘Reference Model’ to establish common terms and concepts Ensure broad participation, including traditional archives (Not restricted to space communities; all participation is welcome!) Focus on data in electronic forms, but recognize that other forms exist in most archives Follow up with additional archive standards efforts as appropriate

Getting Started First open US workshop held October 1995 Variety of government, academic, and industry participation, including National Archives Active US working group was formed US workgroup activities are fully open New participants always welcome Plans, minutes, drafts available from Web Broad international workshops also held Britain and France Issue resolution at CCSDS international workshops

Results Reference Model targeted to several categories of reader Archive designers Archive users Archive managers, to clarify digital preservation issues and assist in securing appropriate resources Standards developers Adopting terminology that crosses various disciplines Traditional archivists Scientific data centers Digital libraries Getting favorable comments wherever exposed

Reference Model for an Open Archival Information System

Open Archival Information System (OAIS) Reference Model standard(s) are developed using a public process and are freely available Information Any type of knowledge that can be exchanged Independent of the forms (i.e., physical or digital) used to represent the information Data are the representation forms of information Archival Information System Hardware, software, and people who are responsible for the acquisition, preservation and dissemination of the information Additional OAIS responsibilities are identified later and are more fully defined in the Reference Model document This reference model is called : Reference Model for an OAIS (Open Archival Information System) These tems have to be explained : In the framework of the archiving reference model elaboration, a glossary has been defined. This is a crucial point for the common understandding of archival concepts 4

Document Organization Introduction Purpose and Scope, Applicability, Rationale, Road Map for Future Work, Document Structure, and Definitions of Terms OAIS Concepts High level view of OAIS functionality and information models OAIS external environment Minimum responsibilities to become an “OAIS” Detailed Models Functional model descriptions and information model perspectives Migration perspectives Media migration, compression, and format conversions Archive Interoperability Criteria to distinguish types of cooperation among archives Annexes Scenarios of existing archives, compatibility with other standards The current version ot the Reference model document is organised as follow The parts in blue will no detailed to day 6

Purpose, Scope, and Applicability Framework for understanding and applying concepts needed for long-term digital information preservation Long-term is long enough to be concerned about changing technologies Starting point for model addressing non-digital information Provides set of minimal responsibilities to distinguish an OAIS from other uses of ‘archive’ Framework for comparing architectures and operations of existing and future archives Basis for development of additional related standards Addresses a full range of archival functions Applicable to all long-term archives and those organizations and individuals dealing with information that may need long-term preservation Does NOT specify any implementation

Model View of an OAIS’s Environment Producer is the role played by those persons, or client systems, who provide the information to be preserved Management is the role played by those who set overall OAIS policy as one component in a broader policy domain Consumer is the role played by those persons, or client systems, who interact with OAIS services to find and acquire preserved information of interest The environment surrounding the OAIS is given by this simple model outside the OAIS are : producers : play the rôle of those who provide the information to preserve management : play the rôle of those who set overall OAIS policy consumers : play the rôle of those who interact with the OAIS services to find information of interest and to access this information OAIS (archive) Producer Consumer Management 7

OAIS Information Definition Information is defined as any type of knowledge that can be exchanged, and this information is always expressed (i.e., represented) by some type of data In general, it can be said that “Data interpreted using its Representation Information yields Information” In order for this Information Object to be successfully preserved, it is critical for an archive to clearly identify and understand the Data Object and its associated Representation Information Interpreted Using its Yields Data Object Representation Information Information Object

Information Package Definition Preservation Description Information Content Information An Information Package is a conceptual container of two types of information called Content Information and Preservation Description Information (PDI)

Information Package Variants Submission Information Package Negotiated between Producer and OAIS Sent to OAIS by a Producer Archival Information Package Information Package used for preservation Includes complete set of Preservation Description Information for the Content Information Dissemination Information Package Includes part or all of one or more Archival Information Packages Sent to a Consumer by the OAIS

External Data Flow Diagram Producer Submission Information Packages OAIS Archival Information Packages Legend = Entity Information Package Data Object = Data Flow = queries This diagram concentrates on the flow of information among producer, Consumers and the OAIS, and does not include flows that involve management query response Dissemination Information Packages orders Consumer 8

OAIS Responsibilities Negotiates and accepts Information Packages from information producers Obtains sufficient control to ensure long-term preservation Determines which communities (designated) need to be able to understand the preserved information Ensures the information to be preserved is independently understandable to the Designated Communities Follows documented policies and procedures which ensure the information is preserved against all reasonable contingencies Makes the preserved information available to the Designated Communities in forms understandable to those communities 11

Detailed Models Overview

Overview of Detailed Models It was decided to do both a functional and an information model of the OAIS Both models were tasked to: Use the models to better communicate OAIS Concepts Use a well established, formal modeling technique Stay as implementation independent as possible Avoid detailed designs

Detailed Models Information Model

General Principles Define classes of “information objects’ that illustrate information necessary to enable Long-term storage and access to Archives The class definition should be implementation Independent Use a variant of Object Modeling Technique (OMT) as a notation (being updated to UML)

OMT Notation Overview Class: Multiplicity of Associations: Class Name Class Exactly one Class Many (zero or more) Aggregation: Assembly Class Class Optional (zero or one) 1+ Class One or more Part -1 Class Part-2 Class Specialization: Association: Association Name Parent Class Class-1 Class-2 Child -1 Class Child-2 Class

Information Objects Information Object Representation 1+ interpreted using Data Physical Digital Bit Sequence

Representation Information The Representation Information accompanying a physical object like a moon rock may give additional meaning, as a result of some analysis, to the physically observable attributes of the rock The Representation Information accompanying a digital object, or sequence of bits, is used to provide additional meaning. It typically maps the bits into commonly recognized data types such as character, integer, and real and into groups of these data types. It associates these with higher level meanings which can have complex inter-relationships that are also described

Recursive Nature of Representation Information Preexisting standards that define primitive data-types Mapping rules that map those primitive data-type into the more complex data-type concept used by the Data Object Other semantic informa-tion that aids in the under-standing of the Data such as a Data Dictionary

Sample Representation Net

Types of Information Used in OAIS

Content Information The information which is the primary object of preservation An instance of Content Information is the information that an archive is tasked to preserve. Deciding what is the Content Information may not be obvious and may need to be negotiated with the Producer The Data Object in the Content Information may be either a Digital Object or a Physical Object (e.g., a physical sample, microfilm)

Preservation Description Information Provenance Information Describes the source of Content Information, who has had custody of it, what is its history Context Information Describes how the Content Information relates to other information outside the Information Package Reference Information Provides one or more identifiers, or systems of identifiers, by which the Content Information may be uniquely identified Fixity Information Protects the Content Information from undocumented alteration

Example of Preservation Description Information Content Information Type Reference Provenance Context Fixity Space Science Data Bibliographic Information Software Package Object Identifier Journal Reference Mission, instrument, and title attribute set ISBN Title Author Name Version number Serial Number Instrument Description Processing History Sensor Description Instrument Instrument mode Decommutation map Software Interface Specifications Printing history Copyright Position in series Manuscripts References Revision Histroy License holder Registration Calibration history Related data sets Mission Funding history Related References Dewy Decimal System Publishing Data Publisher Help file User Guide Related Software Language CRC Checksum Reed-Solomon coding Author Digital signature Cover Certificate Encryption

Descriptive Information Contain the data that serves as the input to documents or applications called Access Aids. Access Aids can be used by a consumer to locate, analyze, retrieve, or order information from the OAIS.

Packaging Information Information which, either actually or logically, binds and relates the components of the package into an identifiable entity on specific media Examples of Packaging Information include tape marks, directory structures and filenames

OAIS Archival Information Package Package (AIP) Packaging Information Package Descriptor derived from delimited by e.g., Information supporting customer searches for AIP e.g., How to find Content information and PDI on some medium Preservation Description Information (PDI) Content Information further described by The AIP is a basic concept in the OAIS. The AIP contains a piece of information that the OAIS has to be preserve. The AIP isq defined to be composed of two types of information objects : one is called the Content Information (CI) and the other is called the Preservation Description Information (PDI) (terminology under discussion) The purpose in making this distinction is to propote a clear difference between that information (the CI) that is the primary focus of archival preservation and that information which is needed to support the long term preservation or the primary information. The AIP is a generic term, it will be specialised in AIC (Archiving Information Collection) and AIU (Archiving Information Unit) e.g., • Hardcopy document • Document as an electronic file together with its format description • Scientific data set consisting of images and text in three electronic files together with format descriptions e.g., • How the Content Information came into being, who has held it, how it relates to other information, and how its integrity is assured 9

AIP Types Based on the difference in Content Object complexity AIUs contain a single Data Object as the Content Object AICs contain multiple AIPs in their Content Objects Each member of an AIC is an AIP containing Content Information and PDI The AIC contains unique PDI on the collection process

Package Descriptors and Access Aids Package descriptors are needed by an OAIS to provide visibility and access to the OAIS holdings Package Descriptors contain 1 or more Associated Descriptions which describe the AIP Content Information from the point of view of a single Access Aid Some example of Access Aids Include: Finding Aids - assist the consumer in locating information of interest Ordering Aids - allow the consumer to discover the cost of and order AIUs of interest Retrieval Aids - enable authorized users to retrieve the AIU described by the Unit Descriptor from Archival Storage

Information Model Summary Presented a model of information objects as containing data objects and representation objects Classified information required for Long-term archiving into 4 classes: Content Information, PDI, Packaging Information and Descriptive Information Described how these classes would be aggregated and related in an AIP to fully describe an instance of Content Information Presented information needed for Access, in addition to that needed for Long-term Preservation Put the Access oriented structures in the context of the other data needed to operate an OAIS

Detailed Models Functional View

General Principles Highlight the major functional areas important to digital archiving Use functional decomposition to clarify the range of functionality that might be encountered Don't decompose beyond two levels to avoid becoming too implementation dependent Provide a useful set of terms and concepts Do not imply that all archives need to implement all the sub-functions Identify some common services which are likely to be needed, and are assumed to be available, as underlying support

Common Services Modern, distributed computing applications assume a number of supporting services Examples of Common Services include: inter-process communication name services temporary storage allocation exception handling security file and directory services

OAIS Functional Entities Descriptive Info. Data Management Descriptive Info. Requests P R O D U C E C O N S U M E R Ingest other information Access SIP AIP AIP DIP Archival Storage Administration We can see, in this view, that the AIP is a specialized object create from a more genenal object called ‘Information package’ MANAGEMENT SIP = Submission Information Package AIP = Archival Information Package DIP = Dissemination Information Package 10

Functional Entities In An OAIS Ingest: This entity provides the services and functions to accept Submission Information Packages (SIPs) from Producers and prepare the contents for storage and management within the archive Archival Storage: This entity provides the services and functions for the storage, maintenance and retrieval of Archival Information Packages Data Management: This entity provides the services and functions for populating, maintaining, and accessing both descriptive information which identifies and documents archive holdings and internal archive administrative data. Administration: This entity manages the overall operation of the archive system Access: This entity supports consumers in determining the existence, description, location and availability of information stored in the OAIS and allowing consumers to request and receive information products

Ingest Functions Schedule Submission Delivery: negotiates a data submission schedule with the producer Receive Submission: provides the appropriate storage capability or devices to receive a SIP from the producer. The Receive SIP function may represent a legal transfer of custody for the CI in the SIP, and may require that special access controls be placed on the contents Generate Archival Information Package: transforms one or more SIPs into one or more AIPs that conforms to the internal data model of the archive. Generate Descriptive Information: extracts Descriptive Information from the AIPs to populate the data management system. Coordinate Updates: responsible for transferring the AIPs to Archival Storage and the Descriptive Information to Data Management

Ingest Data Flow Diagram

Analysis of Archive Issues Using OAIS RM Migration

Digital Migration Digital Migration is defined to be the transfer of digital information, while intending to preserve it, within the OAIS. Focus on preservation of the full information content New information implementation replaces the old OAIS has full control and responsibility over all aspects of the transfer Three major motivators are seen to drive Digital Migrations of Archival Information Packages within an OAIS: Media Decay Increased Cost Effectiveness New Consumer Service Requirements

Digital Migration Approaches Four primary types of digital migration in response to motivators, ordered by increasing risk of information loss: Refreshment Media replacement with no bit changes Replication No change to Packaging Information or Content Information bits Repackaging Some bit changes in Packaging Information Transformation Reversible: Bit changes in Content Information are reversible by an algorithm Non-reversible: Bit changes in Content Information are not reversible by an algorithm

Access Preservation Effective access to digital information requires the use of software Application Programming Interfaces (APIs) may be cost-effectively maintained across time by an OAIS when: API is not too complex API is applicable to a wide variety of AIUs API source code may be ported to new environments Extensive testing is needed to ensure against information loss Preservation of executables by full emulation of underlying hardware is problematic Hard to know what is the information being preserved May not be possible to fully emulate associated devices

Analysis of Archive Issues Using OAIS RM Archive Associations

Archive Interoperability Motivators Users of multiple OAIS archives have reasons to wish for some interoperability or cooperation among the OAISs. Consumers Common finding aids to aid in locating information over several OAIS archives Common Package Descriptor schema for access Common DIP schema for dissemination, or a single global access site. Producers common SIP schema for submission to different archives a single depository for all their products. Managers Cost reduction through sharing of expensive hardware increasing the uniformity and quality of user interactions with the OAIS

Categories of Archive Interactions Independent: no knowledge by one OAIS of Standards implemented at another Cooperating: Potentially common submission standards, and common dissemination standards, but no common access. One archive may make subscription requests for key data at the cooperating archive Federated: Access to all federated OAIS is provided through a common set of access aids that provide visibility into all participating OAISs. Global dissemination and Ingest are options Shared resources: An OAIS in which Management has entered into agreements with other OAISs is to share resources to reduce cost. This requires various standards internal to the archive (such as ingest-storage and access-storage interface standards), but does not alter the community’s view of the archive

Federated Archives Local Consumer Global OAIS 1 Consumer Dissemination Information Package (Optional) Ingest Access OAIS 1 Administration Access Access Global Consumer Common Catalog Administration Administration OAIS 2 Ingest Access Access Local Consumer Dissemination Information Package (Optional)

Levels of Autonomy in Associated Archives No interactions and therefore no association Associations that maintain your autonomy. You have to do certain things to participate, but you can leave the association without notice or impact to you. Associations that bind you by contract. To change the nature of this association you will have to re-negotiate the contract. The amount of autonomy retained depends on how difficult it is to negotiate the changes.

Reference Model Summary Reference model is to be applicable to all digital archives, and their Producers and Consumers Identifies a minimum set of responsibilities for an archive to claim it is an OAIS Establishes common terms and concepts for comparing implementations, but does not specify an implementation Provides detailed models of both archival functions and archival information Discusses OAIS information migration and interoperability among OAISs

Reference Model Acceptance Reference model has been getting good reviews Society of American Archivists 1997 annual meeting NAGARA 1998 Annual Meeting Various international conferences Major context for June 1998 Digital Archive Directions (DADs) workshop hosted by NARA http://ssdoo.gsfc.nasa.gov/nost/isoas/dads/ Framework for October 1999 Archival Workshop on Ingest, Identification, and Certification (AWIICS) hosted by NARA http://ssdoo.gsfc.nasa.gov/nost/isoas/awiics/ws.html

DADs Workshop Recommendations Working groups identified several ‘best practices’ and standards desired, including: Recommended data ingest methodology Best practices for digitizing analogue data Best practices for media selection, testing and usage Best practices for error control through the archive Archival Submission Information Package standard Consumer Archive Interface standard Unique Archival Information Package Identifier standard AIP Content Layered Model and Standard APIs report Plenary recommended a coordination function be established Promote the reference model Promote coordination of work on best practices and standards Promote development of an archive accreditation method

AWIICS Conclusions A diverse community of science data centers, libraries, electronic records and traditional archives sees the benefit, and is willing to participate, in developing standards in the following areas: Ingest Methodology for producer interactions with the archive Certification of digital archives and preservation methodology Access scenarios and derived requirements for identification of, and access to, archived information

Reference Model Status Ultimate success of OAIS Reference Model effort depends on obtaining adequate review and comment CCSDS Reference Model Red Book released August 1999 http://ssdoo.gsfc.nasa.gov/nost/isoas/ref_model.html ISO Draft International Standard (DIS) expected May 2000 Same content as CCSDS Red Book Held up by ISO TC20 secretariat backlog Comments are actively solicited Participate in various ways: ISO TC20/SC 13 review in your country CCSDS review by your space agency Send comments to donald.sawyer@gsfc.nasa.gov All comments will be considered and non-editorial comments will get a response