Ontotext are pleased to announce the second BETA release of OWLIM
version 5.0 <http://www.ontotext.com/owlim> featuring:
* *Transaction management and isolation mechanisms* have been
completely refactored. The previous strategy used lazy writing of
modified database pages, such that dirty pages were only flushed to
disk when further updates occur and no more memory is available.
While extremely fast, the problem with this approach is that there
is a considerable recovery time associated with replaying the
transaction log after an abnormal termination. The new mechanism
uses two modes: 'bulk-loading' (fast) with similar behaviour to
previous versions and 'normal' (safe) where database modifications
are flushed to disk as part of the commit operation. When running in
safe mode, *database recovery is instant* and there is a
*significant improvement in concurrency between updates and queries*.
* *New context indices* can be used to improve query performance when
data is modelled using many named graphs. These are switched on and
off using a single configuration parameter enable-context-index
* The *SPARQL 1.1 Graph Store HTTP Protocol* is now supported
according to the W3C Working Draft
<http://www.w3.org/TR/sparql11-http-rdf-update/> from the 12th May
2011. This provides a REST interface for managing collections of
graphs, using either directly or indirectly named graphs.
* *Sesame <http://www.openrdf.org>**2.6.5* with many bug-fixes and
updates to bring SPARQL 1.1 Query
<http://www.w3.org/TR/2012/WD-sparql11-query-20120105/> support up
to the latest W3C Working Draft from the 5th January 2012. NOTE:
This beta release is bundled with a snapshot version of Sesame. The
final release of OWLIM will coincide with the official Sesame 2.6.5
release
* *Significant reduction in disk-space requirements* is achieved with
the following modifications:
o *Index compression* can now be used to reduce disk storage
requirements by using zip compression on database pages. This
feature if off by default, but can be switched on when creating
a new repository. The configuration parameter
index-compression-ratio can be set to -1 (the default value
indicating no compression) or a value in the range 10-50
<https://confluence.ontotext.com/pages/createpage.action?spaceKey=OWLIMint&title=10-50&linkCreation=true&fromPageId=16191743>
indicating the desired percentage reduction in page sizes. Any
pages that can not be compressed by the specified amount are
stored uncompressed. Therefore a compression ratio that is too
aggressive will not bring many benefits. Experiments have shown
that for large datasets a value of about 30% is close to optimal
and can lead to storage space savings of 50%.
o *Restructuring of the triple indices* has also led to a
reduction in disk-space requirements of around 18% independent
of the compression functionality
o *Entity compression* is a modification that reduces the storage
requirements for the lookup table that maps between internal
identifiers and resources. This is transparent to the user and
happens automatically. More disk space reductions are apparent
using this version.
* A new *literal index* is created automatically for numeric and
date/time data-types. The index is used during query evaluation if a
query or a subquery (e.g. union) has a filter that is comprised of a
conjunction of literal constraints, e.g. FILTER(?x >= 3 && ?y <= 5
&& ?start > "2001-01-01"^^xsd:date). Other patterns, including those
that use negation, will not use the index for this version of OWLIM.
* All *control queries now use SPARQL Update syntax* (used mostly to
control the Lucene-based full-text search, RDF Rank and geo-spatial
plug-ins). This has a number of advantages, namely:
o No special control query pseduo-graph is required by the
Replication Cluster master in order to identify control queries
that must be pushed to all worker nodes
o SPARQL Updates use the corresponding SPARQL update protocol, so
they can be automatically processed by load-balancers that
examine URL patterns
o It is more consistent with the SPARQL language, since these
'control queries' cause a change of state in OWLIM
* *Incremental Lucene-based full-text search index* for updating the
index for specific resources or all un-indexed resources. Using this
technique can avoid the more expensive approach of rebuilding the
whole index frequently.
* *Incremental RDF Rank* allows the RDF rank for specific resources to
be (re-)computed as directed by the user. This technique can avoid
the more expensive approach of rebuilding all RDF Rank values
frequently.
* The *getting started* application has been restructured so that it
now works with remote repositories.
*Known problems*
* There are several outstanding fixes to be done in Sesame, which can
cause incorrect query results when using sub-queries.
* The behaviour of the 'include inferred' checkbox in the Sesame
Workbench is unpredictable when using OWLIM repositories.
* This version of OWLIM is *not backwardly compatible* with any
previous version. This means that images created with OWLIM 4.3 and
before will not work correctly with OWLIM 5.0 and must be
re-created. There have been a great many modifications to the
storage files, indexing structures, etc, and upgrade mechanisms have
proven too complex and probably slower than re-loading the database
anyway. Please *do not attempt to upgrade to OWLIM 5.0 unless you
drop and recreate all databases*. A migration tool, which allows for
automated re-loading of data from any Sesame-accessible repository,
will be provided to ease the transition.
Full documentation for all OWLIM editions is available online
<http://owlim.ontotext.com> (click on the OWLIM 5.0 beta link on the
left hand side).
The OWLIM team
March 2012
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