5.1 DIGITAL MIGRATION - Revision history

Hlhours at 13:25, 5 October 2015

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	Digital Migration is defined to be the transfer of digital information, while intending to preserve it, within the OAIS. It is distinguished from transfers in general by three attributes:		Digital Migration is defined to be the transfer of digital information, while intending to preserve it, within the OAIS. It is distinguished from transfers in general by three attributes:

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	[[5.1.3.5 Distinguishing AIP Versions, AIP Editions and Derived AIPs]]		[[5.1.3.5 Distinguishing AIP Versions, AIP Editions and Derived AIPs]]


			'''--Please retain original text above for reference. Propose amendments or additions below this line or respond using the Discussion tab above--'''

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Hlhours at 14:11, 13 August 2015

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	[[5.1.1 DIGITAL MIGRATION MOTIVATORS]]		[[5.1.1 DIGITAL MIGRATION MOTIVATORS]]

	[[5.1.2 MIGRATION CONTEXT]]		[[5.1.2 MIGRATION CONTEXT]]

	[[5.1.3 MIGRATION TYPES]]		[[5.1.3 MIGRATION TYPES]]

	[[5.1.3.1 Refreshment]]		[[5.1.3.1 Refreshment]]

	[[5.1.3.2 Replication]]		[[5.1.3.2 Replication]]

	[[5.1.3.3 Repackaging]]		[[5.1.3.3 Repackaging]]

	[[5.1.3.4 Transformation]]		[[5.1.3.4 Transformation]]

	[[5.1.3.5 Distinguishing AIP Versions, AIP Editions and Derived AIPs]]		[[5.1.3.5 Distinguishing AIP Versions, AIP Editions and Derived AIPs]]

Hlhours at 14:10, 13 August 2015

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Hlhours at 07:56, 13 August 2015

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	Key functional and information modeling concepts from section 4, as they relate to migration perspectives, are summarized in figure 5-1.		Key functional and information modeling concepts from section 4, as they relate to migration perspectives, are summarized in figure 5-1.


	'''Figure 5-1: Conceptual View of Relationships among Names and AIP Components'''		'''Figure 5-1: Conceptual View of Relationships among Names and AIP Components'''

	The OAIS Consumer interface in Access provides one or more Content Information IDs, with associated name spaces, to assist in identifying a particular Content Information object of interest. One or more of these Content Information IDs will be included in the PDI Reference Information associated with that Content Information object. The Descriptive Information in Data Management will map each of these IDs to the same AIP ID. The Access Function uses this information to obtain the AIP ID and gives it to Archival Storage to retrieve the associated AIP.		The OAIS Consumer interface in Access provides one or more Content Information IDs, with associated name spaces, to assist in identifying a particular Content Information object of interest. One or more of these Content Information IDs will be included in the PDI Reference Information associated with that Content Information object. The Descriptive Information in Data Management will map each of these IDs to the same AIP ID. The Access Function uses this information to obtain the AIP ID and gives it to Archival Storage to retrieve the associated AIP.

Hlhours at 07:55, 13 August 2015

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	– New Consumer-Service Requirements: The Consumers of an OAIS also experience the benefits of new technologies and consequently raise their expectations of the types and levels of service they expect from an OAIS. These increased services may require new forms of DIPs to service particular Designated Communities, which in turn may drive an OAIS to hold new forms of AIPs to reduce output conversions. Additionally, AIPs typically go through popularity swings and the OAIS may need to provide different levels of access performance to meet Consumer demands over time. This is likely to be satisfied by moving some AIPs to different media that provide increased or decreased levels of access performance. Finally, the Designated Community for a given AIP may be broadened, resulting in the need to revise AIP forms so as to be understandable and usable by this broader community. All of these can result in the migration of AIPs within an OAIS.		– New Consumer-Service Requirements: The Consumers of an OAIS also experience the benefits of new technologies and consequently raise their expectations of the types and levels of service they expect from an OAIS. These increased services may require new forms of DIPs to service particular Designated Communities, which in turn may drive an OAIS to hold new forms of AIPs to reduce output conversions. Additionally, AIPs typically go through popularity swings and the OAIS may need to provide different levels of access performance to meet Consumer demands over time. This is likely to be satisfied by moving some AIPs to different media that provide increased or decreased levels of access performance. Finally, the Designated Community for a given AIP may be broadened, resulting in the need to revise AIP forms so as to be understandable and usable by this broader community. All of these can result in the migration of AIPs within an OAIS.

	~~== 5.1.1 DIGITAL MIGRATION MOTIVATORS ==~~

			== 5.1.2 MIGRATION CONTEXT ==

	~~Three major motivators are seen to drive Digital Migrations of AIPs within an OAIS. These are:~~

	– Improved Cost-Effectiveness: The rapid pace of hardware (e.g., disk/tape drives) and software evolution provides greatly increasing storage capacities and transfer bandwidths at reducing costs. It also drives the obsolescence of some media types well before they have time to decay and it drives the obsolescence of software employed as part of Representation Information. In addition, improved AIP packaging designs may be less dependent on underlying media and supporting systems, and therefore simplified migration efforts may be recognized. To remain cost-effective, an OAIS must take advantage of these technologies. Depending on the particular technologies involved, the AIP information may have to be moved to new media types not previously supported, and it may have to revise its AIP implementations to maintain information preservation.

	– New Consumer-Service Requirements: The Consumers of an OAIS also experience the benefits of new technologies and consequently raise their expectations of the types and levels of service they expect from an OAIS. These increased services may require new forms of DIPs to service particular Designated Communities, which in turn may drive an OAIS to hold new forms of AIPs to reduce output conversions. Additionally, AIPs typically go through popularity swings and the OAIS may need to provide different levels of access performance to meet Consumer demands over time. This is likely to be satisfied by moving some AIPs to different media that provide increased or decreased levels of access performance. Finally, the Designated Community for a given AIP may be broadened, resulting in the need to revise AIP forms so as to be understandable and usable by this broader community. All of these can result in the migration of AIPs within an OAIS.

	~~5.1.2 MIGRATION CONTEXT~~

	Key functional and information modeling concepts from section 4, as they relate to migration perspectives, are summarized in figure 5-1.		Key functional and information modeling concepts from section 4, as they relate to migration perspectives, are summarized in figure 5-1.

Hlhours at 07:54, 13 August 2015

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	– New Consumer-Service Requirements: The Consumers of an OAIS also experience the benefits of new technologies and consequently raise their expectations of the types and levels of service they expect from an OAIS. These increased services may require new forms of DIPs to service particular Designated Communities, which in turn may drive an OAIS to hold new forms of AIPs to reduce output conversions. Additionally, AIPs typically go through popularity swings and the OAIS may need to provide different levels of access performance to meet Consumer demands over time. This is likely to be satisfied by moving some AIPs to different media that provide increased or decreased levels of access performance. Finally, the Designated Community for a given AIP may be broadened, resulting in the need to revise AIP forms so as to be understandable and usable by this broader community. All of these can result in the migration of AIPs within an OAIS.		– New Consumer-Service Requirements: The Consumers of an OAIS also experience the benefits of new technologies and consequently raise their expectations of the types and levels of service they expect from an OAIS. These increased services may require new forms of DIPs to service particular Designated Communities, which in turn may drive an OAIS to hold new forms of AIPs to reduce output conversions. Additionally, AIPs typically go through popularity swings and the OAIS may need to provide different levels of access performance to meet Consumer demands over time. This is likely to be satisfied by moving some AIPs to different media that provide increased or decreased levels of access performance. Finally, the Designated Community for a given AIP may be broadened, resulting in the need to revise AIP forms so as to be understandable and usable by this broader community. All of these can result in the migration of AIPs within an OAIS.
	5.1.1 DIGITAL MIGRATION MOTIVATORS
			== 5.1.1 DIGITAL MIGRATION MOTIVATORS ==


	Three major motivators are seen to drive Digital Migrations of AIPs within an OAIS. These are:		Three major motivators are seen to drive Digital Migrations of AIPs within an OAIS. These are:
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	The ways in which AIPs are implemented will have a major influence on both the level of automation and the probability of information loss during migrations. Good AIP designs can both increase migration automation and reduce information loss probabilities. To better understand the impacts of these factors on AIP migrations it is useful to categorize migrations into several types and then to consider some issues associated with selected implementation approaches.		The ways in which AIPs are implemented will have a major influence on both the level of automation and the probability of information loss during migrations. Good AIP designs can both increase migration automation and reduce information loss probabilities. To better understand the impacts of these factors on AIP migrations it is useful to categorize migrations into several types and then to consider some issues associated with selected implementation approaches.

	5.1.3 MIGRATION TYPES
			== 5.1.3 MIGRATION TYPES ==


	Based on the models and concepts above, it is possible to identify four primary Digital		Based on the models and concepts above, it is possible to identify four primary Digital
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	The number of correctable bit errors on a CD-ROM disk has reached a dangerous point and the decision is made to replace it with an exact copy. Once the equivalence between the two has been checked, the new CD-ROM replaces the old CD-ROM and Refreshment has taken place. All AIP components on the CD-ROM are unaltered.		The number of correctable bit errors on a CD-ROM disk has reached a dangerous point and the decision is made to replace it with an exact copy. Once the equivalence between the two has been checked, the new CD-ROM replaces the old CD-ROM and Refreshment has taken place. All AIP components on the CD-ROM are unaltered.

	5.1.3.2 Replication
			== 5.1.3.2 Replication ==


	A migration involves Replication when there are no bit changes to the Packaging Information, the Content Information, and the PDI. Ensuring that none of these bits has changed may be a significant effort, depending on the implementation. The following scenario is an example of Replication:		A migration involves Replication when there are no bit changes to the Packaging Information, the Content Information, and the PDI. Ensuring that none of these bits has changed may be a significant effort, depending on the implementation. The following scenario is an example of Replication:
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	5.1.3.3 Repackaging
			== 5.1.3.3 Repackaging ==


	A migration involves Repackaging when there is some change to the Packaging Information during the transfer. The Packaging Information plays the critical role of delimiting and relating, at a minimum, the Content Information and PDI. If the Content Information and PDI are themselves composed of multiple components, the Packaging Information may be asked to delimit and relate these as well. These are implementation decisions that the OAIS needs to explicitly recognize. The following scenario is an example of Repackaging:		A migration involves Repackaging when there is some change to the Packaging Information during the transfer. The Packaging Information plays the critical role of delimiting and relating, at a minimum, the Content Information and PDI. If the Content Information and PDI are themselves composed of multiple components, the Packaging Information may be asked to delimit and relate these as well. These are implementation decisions that the OAIS needs to explicitly recognize. The following scenario is an example of Repackaging:
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	The Content Information and PDI bits for an AIC are defined to be an aggregation of AIUs where each AIU consists of the body of three files on a CD-ROM together with their file names, file attributes, and directory names. The Packaging Information is the bits used to implement the file and directory structure that provides access to each of the three file instances, but does not include the actual file and directory names. There may be thousands of AIU instances on a single CD-ROM. The transfer of this AIC to a new media type that employs a new representation for the file and directory structure that has fewer file attributes may result in a Non-Reversible Transformation type of Migration as well as a Repackaging migration. This is a Transformation because the Content Information that originally was stored in the file and directory structures must be re-distributed among the new file and directory structures and probably within the body of the files themselves. This is a Non-Reversible Transformation if there is no algorithmic one-to-one mapping between the resulting file and directory structures and file contents, and the original file and directory structures. It is a Repackaging because there is a new implementation of the directory and file structure, which was taken to be part of the packaging. The practice of encoding Content Information into a file or directory name increases the risk of information loss because evolution of a data management environment is facilitated by being able to update directory and file names as needed.		The Content Information and PDI bits for an AIC are defined to be an aggregation of AIUs where each AIU consists of the body of three files on a CD-ROM together with their file names, file attributes, and directory names. The Packaging Information is the bits used to implement the file and directory structure that provides access to each of the three file instances, but does not include the actual file and directory names. There may be thousands of AIU instances on a single CD-ROM. The transfer of this AIC to a new media type that employs a new representation for the file and directory structure that has fewer file attributes may result in a Non-Reversible Transformation type of Migration as well as a Repackaging migration. This is a Transformation because the Content Information that originally was stored in the file and directory structures must be re-distributed among the new file and directory structures and probably within the body of the files themselves. This is a Non-Reversible Transformation if there is no algorithmic one-to-one mapping between the resulting file and directory structures and file contents, and the original file and directory structures. It is a Repackaging because there is a new implementation of the directory and file structure, which was taken to be part of the packaging. The practice of encoding Content Information into a file or directory name increases the risk of information loss because evolution of a data management environment is facilitated by being able to update directory and file names as needed.

	5.1.3.5 Distinguishing AIP Versions, AIP Editions and Derived AIPs
			== 5.1.3.5 Distinguishing AIP Versions, AIP Editions and Derived AIPs ==


	Unless a Digital Migration involves Transformation, it is not considered to create a new AIP Version and it is not required that its PDI be updated. In other words, the AIP version is considered to be independent of Refreshment, Replication, and Repackaging that does not affect the Content Information or PDI. This does not mean that the OAIS does not track such migrations; rather it is not required to update the PDI as part of such tracking. It is expected that the OAIS will verify that such migration have not altered the Content Information or PDI and that any repackaging still binds the same components with the same relationships. It is also expected that the OAIS will track the existence of these events, including the verifications made, as a part of its larger operational provenance as this will lend additional evidence concerning the Authenticity of its holdings. If such migration processes are carried out entirely within Archival Storage, the AIP ID remains the same and there is no implied impact to Associated Descriptions or Access Aids.		Unless a Digital Migration involves Transformation, it is not considered to create a new AIP Version and it is not required that its PDI be updated. In other words, the AIP version is considered to be independent of Refreshment, Replication, and Repackaging that does not affect the Content Information or PDI. This does not mean that the OAIS does not track such migrations; rather it is not required to update the PDI as part of such tracking. It is expected that the OAIS will verify that such migration have not altered the Content Information or PDI and that any repackaging still binds the same components with the same relationships. It is also expected that the OAIS will track the existence of these events, including the verifications made, as a part of its larger operational provenance as this will lend additional evidence concerning the Authenticity of its holdings. If such migration processes are carried out entirely within Archival Storage, the AIP ID remains the same and there is no implied impact to Associated Descriptions or Access Aids.

Hlhours at 07:53, 13 August 2015

2015-08-13T07:53:49Z

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Hlhours: Created page with "Digital Migration is defined to be the transfer of digital information, while intending to preserve it, within the OAIS. It is distinguished from transfers in general by three..."

2015-08-12T13:40:30Z

Created page with "Digital Migration is defined to be the transfer of digital information, while intending to preserve it, within the OAIS. It is distinguished from transfers in general by three..."

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Digital Migration is defined to be the transfer of digital information, while intending to preserve it, within the OAIS. It is distinguished from transfers in general by three attributes:

– a focus on the preservation of the full information content intended for preservation;

– a perspective that the new archival implementation of the information is a replacement for the old; and

– full control and responsibility over all aspects of the transfer resides with the OAIS.

It should be noted that ‘transfer’ as found in the definition of Digital Migration is used in a broad way such that when any changes are made to Content Information or to PDI bits for the purpose of information preservation, then this is a Digital Migration even if it appears the changes occurred ‘in place’.