suggestion for a re-implementation of Bundles in the DSpace data model
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Key: DS-893
URL: https://jira.duraspace.org/browse/DS-893
Project: DSpace
Issue Type: Improvement
Components: DSpace API
Affects Versions: 1.8.0
Reporter: Bill Hays
Preliminary ideas for a new implementation of "Bundle" in the DSpace data model
Current database model relationships:
Item <- Item2Bundle -> Bundle <- Bundle2Bitstream -> Bitstream
Current java object model relationships:
Item <-> Bundle <-> Bitstream
Proposed database model relationships (1):
Item <- Item2Bitstream -> Bitstream(id, ..., bundlename, ...)
or even more succinctly:
Item <- Bitstream(id, item_id, bundlename, ...)
In current DSpace, there is no realized benefit from the container complexity
in the current model for Bundles.
This first step in the proposal removes the Bundle table and directly
associates Bitstream to Item. The concept of "bundle" is replaced by an enum
field in the Bitstream that identifies a bundle type (ORIGINAL, THUMBNAIL,
etc). Functionally this is very similar to what we get now: A bitstream
belongs to one item and is associated with one bundle. The bundle names are
not constrained, but some names are expected in various parts of the codebase.
Proposed database model relationships (2):
Item <- Bitstream -> MBundle(id, name, collection_id, derivative ...)
This variation replaces the bundlename enum with a new class and database table
"MBundle." Here bundles are not implemented as containers but are an
associated type concept for a bitstream. With the association to a collection,
bundles can be managed per collection or use a default set. Other properties
of MBundle can be added to further enhance management capabilities, e.g.:
isDerivative - identify bundles for Thumbnails and DerivativeText
isVisible - indicate that the related bitstreams should be visible in
display contexts
isReserved - such as for very large "source" objects not for display or
filtermedia
[needs work - how complex does bundle "metadata" need to be?]
Issues:
Primary Bitstream Id: This is currently only used for the ORIGINAL bundle, so
conceptually there is one per item. Note that the current model (API and
database) allows for multiple ORIGINAL bundles which therefore allows multiple
primary bitstream ids; however, the implementation doesn't expose this
possibility.
Possible replacement API calls, depending on the implementation:
item.setPrimaryBitstream(Bitstream b)
bitstream.isPrimary(Boolean b)
Various db solutions:
item.primaryBitstreamId - not standard database normalization but
consistent with dspace practice
item2bitstream.primaryBitstream - a boolean, standard normalization but
requires some management to avoid duplicates
mbundle.primaryBitstreamId - not standard database normalization but
consistent with dspace practice
item.primaryBitstream - a boolean, standard normalization but requires some
management to avoid duplicates
In the event that someone has used primaryBitstreamId in non-ORIGINAL
bundles for special purposes, only 3 or 4 would work.
Affected Java code: Item and Bitstream would need to be adjusted. This is
fairly low-level so should not be visible to much of the API. Group
authorizations would need some work (this has not been fully analyzed). Custom
code that uses the API might be affected. Custom SQL such as for reporting
might break, but the replacement is shorter code. Collection management of
bundles types would need a new tab on the collection page (XMLUI).
Upgrading a DSpace instance: The database can be modified with queries. No
affect on assetstores.
Benefits:
Simpler, more concise model which removes unused/unnecessary containership
structure.
Enhanced bitstream management with bundle properties.
Enumeration of names instead of uncontrolled strings, preventing typos in
bundle names (e.g. from ItemImport)
Provides easy solution to making derivative bitstreams visible.
Moving bitstreams between bundles does not require deleting and re-adding
the bitstream.
Fixes data model problem with primary bitstream and multiple bundles with
the same name
Drawbacks:
Not a backwardly compatible change. A fundamental change to the data model.
Custom SQL code connecting using bundles will require rework.
Summary:
Bundles are categories for Bitstreams and do not need to be imlemented as
containers.
Bundles could be improved with added metadata and management features.
The current Bundle implementation may not be a priority issue to merit the
work suggested. However, the ideas
above may be suggestive for other work, including metadata for all DSpace
objects and exposing the data model
to external systems (e.g. Fedora)
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