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https://issues.apache.org/jira/browse/JENA-2006?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17244038#comment-17244038
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ASF subversion and git services commented on JENA-2006:
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Commit 3ca8d0346049cae0bd764e66388b1991c7cd110b in jena's branch
refs/heads/master from Andy Seaborne
[ https://gitbox.apache.org/repos/asf?p=jena.git;h=3ca8d03 ]
Merge pull request #880 from afs/dataset-prefixes
JENA-2006: DatasetGraph prefixes
> Dataset prefixes
> ----------------
>
> Key: JENA-2006
> URL: https://issues.apache.org/jira/browse/JENA-2006
> Project: Apache Jena
> Issue Type: Improvement
> Reporter: Andy Seaborne
> Assignee: Andy Seaborne
> Priority: Major
> Fix For: Jena 3.18.0
>
> Time Spent: 1h
> Remaining Estimate: 0h
>
> Summary:
> Add API calls:
> {{DatasetGraph.prefixes()}} -> {{PrefixMap}}
> {{Dataset.getPrefixMapping()}} -> {{PrefixMapping}}
> Rework internal implementation code to reflect this.
> Clearup the different handling of prefixes; switch to a consistent provision
> of a dataset prefix map. Remove {{DatasetPrefixStorage}} (multiple prefix
> maps per dataset).
> My first attempt of this work was to use {{DatasetPrefixStorage}}
> consistently but it ended up as a lot of classes mirroring PrefixMap
> implementations. Because input formats only have prefixes by datasets, not
> individual graph, the extra feature of multiple prefix maps can only be used
> by API and it just doesn't seem worth the effort and extra code. It was
> quicker doing the final form - "one prefix map per dataset" than the more
> complicated form.
> More details:
> "TDB" means both TDB1 and TDB2.
> The main use case for prefixes is set as part of data parsing and use for
> output to abbreviate URIs.
> For output, we know that URI->prefixed name is a performance critical
> operation. It is optimized in {{PrefixMapStd}}. This does not change. The
> writers copy prefixes into a {{PrefixMapStd}} which has a fast-path for the
> common case of split at last "/" or "#" and a reverse map from URI to prefix.
> Mostly, up to now, implementation has been "store the prefixes in the default
> graph" and while TDB stores multiple set of prefixes for each dataset so that
> here is the possibility of graphs in the same dataset having different
> prefixes, it used the default graph as well. Output has never made use of
> multiple prefixes per dataset.
> The {{PrefixMapping}} API presumes a reverse mapping and the API contract is
> part of the Model API (Model extends PrefixMapping). The other odd feature of
> {{PrefixMapping}} is that there is no direct access to the prefixes as a map,
> only a copy form.
> {{PrefixMap}} is simpler with the needs of parsers and storage implementation
> in mind.
> The idea is that {{PrefixMapping}} is to be considered to be part of the
> Dataset/Model/Statement/Resource APIs. There is a legacy quirk that Graph has
> "getPrefixMapping".
> There will be adapters between the two viewpoints. Aside from the implicit
> contract of {{PrefixMapping}} following XML qname rules, while Turtle is less
> restrictive, the functionality can be mapped both ways.
> Mostly the XML-rules contract has been moved into the writers themselves in
> previous iterations of implementation improvement. The adapters are
> lightweight objects, with no state other than the object that adapt and
> "double adapting" actually removes wrappers and returns the underlying
> prefixes object.
> The improved way:
> Basic datasets (DatasetGraphMap and DatasetGraphMapLink) - dataset prefixes
> are the default graph prefixes.
> TIM: All graphs in the dataset have the same prefix map. The PrefixMap is
> thread-safe but isn't transactional (possible future work if needed).
> TDB1, TDB2: These have there own, more general prefix storage but the
> additional feature is not exposed. All graphs in the dataset have the same
> prefix map. There is no change to on-disk format.
> SDB: As before. There is no change to on-disk format.
> The nulls (DatasetGraphZero and DatasetGraphSink): Sink is "forget updates",
> Zero is "empty, no updates": Suitably misbehaved implemented of the
> {{PrefixMap}} API.
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