18.104.22.168 Collection Descriptions
The Collection Description is a subtype of the Package Description that has added structures to better handle the complex Content Information of an AIC. The Collection Description, which is modeled in figure 4-24, contains the information classes that are contained in the Unit Description.
There are two types of Associated Description in a Collection Description:
– There is one Overview Description that describes the collection as a whole.
– There are zero or more Member Descriptions that separately describe each member of the collection.
Figure 4-24: Collection Description
The required Associated Description in a Collection Description provides information for Ordering Aids that provide a user with access to the entire set of Content Information of the associated AIC and the PDI for the AIC, but not necessarily to the individual AIPs contained in the AIC. The Collection Description may contain the Package Descriptions of the AIPs contained in the AIC. This containment relationship is logical in that the AIC may either include the Package Descriptions of member Information Packages directly or, more commonly, use pointers to the Package Descriptions of the member Information Packages.
This list of the Package Descriptions for contained AIPs in an AIC could provide Access Aids with a method to Retrieve or Order individual members of the AIC.
It also allows alternative concepts for the implementation of Finding Aids that enable the Consumer to locate AIPs of interest that are contained in an AIC. The Associated Descriptions that provide data for these Finding Aids could be implemented either in a centralized fashion searching an Associated Description in the Collection Description or in a distributed fashion by searching the Associated Description of each member Package Description.
Another important benefit of the Collection Descriptions is the ability to define new Access Collections. An Access Collection may be based on new data mining results or it may reflect current phenomena or areas of interest that may not be of permanent interest. Examples of an Access Collection in an OAIS for digital movies might be a new arrivals collection or a ‘twenty most popular titles’ collection that is updated periodically. Another example of an Access Collection is a collection based on the results of a pattern recognition algorithm that has not been verified.
To create an Access Collection, an Archive would create a Collection Description that did not have an associated AIC. The Collection Description could have a customized Associated Member Description that documented the newly mined description data for each member AIP. A specialized finding aid could use this new Associated Member Description in conjunction with existing Associated Descriptions in the Package Description information of each member AIP to locate AIPs of interest to the user. The Package Descriptions of contained AIPs would also supply data for an Ordering Aid, which would allow the Consumer to order the Information Packages of interest to the Consumer.
If an OAIS decides that an Access Collection is valuable enough to be preserved for the Long Term, it can store the required Content Information and PDI in Archival Storage thus creating a new AIC.
Another important application of Access Collections is the concept of locating some members of a collection that have been scheduled for ingest at a future time. In this case, the Associated Descriptions supporting a Finding Aid would allow future AIPs to be located. However, the Associated Description for the Ordering Aid and/or the Retrieval Aid would contain the information that this product was not currently available and allow the user to enter an Event Based Order which would be triggered when the AIP of interest became available.