Monthly Archives: May 2012

Setting up a local DBpedia 3.7 mirror with Virtuoso 6.1.5+

Newer version available: Setting up a Linked Data mirror from RDF dumps (DBpedia 2015-04, Freebase, Wikidata, LinkedGeoData, …) with Virtuso 7.2.1 and Docker (optional)

Nearly 1.5 years after i initially published a post about how to setup a local DBpedia mirror i recently revisited the problem myself to setup a local mirror of the DBpedia 3.7.

Unlike the previous updates so many things have changed that I decided to put them into a separate post instead of continuing to update the old one making it more and more complicated.
Two of the most severe changes are that Virtuoso 6.1.5+ includes a setting making the importer more robust so the repacking of the files isn’t needed anymore and the changes of DBpedia 3.7 to also provide internationalized versions causing a couple of problems / inconsistencies.

In this step by step guide I’ll tell you how to install a local mirror of the DBpedia 3.7 hosting a combination of the regular English and the i18n German datasets adding up to nearly half a billion triples!!!
Let’s jump in.


DBpedia 3.7 + 3.7-i18n dataset. Virtuoso 6.1.5+ (Actually it’s a 6.1.6-dev version with some bugfixes for the DBpedia VAD files, as detailed below). Ubuntu 12.04 LTS.


A strong machine with root access and enough RAM: We used a VM with 4 Cores and 32 GBs of RAM. For installing i recommend more than 128 GB free HD space, especially for downloading and repacking the datasets, as well as the growing database file when importing (mine grew to 45 GBs).

Let’s go

Download and install virtuoso

Go and download virtuoso opensource:

Initially i started this guide with virtuoso-opensource-6.1.5 from, but later on in the process i ran into problems with the DBpedia VAD file which is used for resolving and content negotiation of instances via http. If you only intend to use the sparql endpoint you can download that version, but if you want to be able to actually resolve the local versions of the pages with content negotiation, you need a version with some bugfixes from github: If at the time of you reading this 6.1.6 is officially released, I’d probably use the official release.

To get that version from github do the following:

cd ~
git clone git:// virtuoso-opensource
cd virtuoso-opensource
# the following command will actually set your working directory to the
# correct revision
git checkout 674df8668d7dd3018b3a8a14c23702c583d64961

(Skip the following if you got the version from github.)

If you downloaded one of the release .tar.gz files instead: Put the file in your home dir on the server, then do the following.

cd ~
tar -xvzf virtuoso-*
cd virtuoso-opensource-6.1.5 # or 6.1.6, depending what you got

Alright, now no matter how you got that virtuoso version do the following to install the prerequisites and then build virtuoso:

sudo aptitude install libxml2-dev libssl-dev autoconf libgraphviz-dev
     libmagickcore-dev libmagickwand-dev dnsutils gawk bison flex gperf
export CFLAGS="-O2 -m64"
./configure --with-layout=debian
# NOTICE: this will _not_ install into /usr/local but into /usr
# (so might clash with packages by your distribution if you install
# "the" virtuoso package)
# You'll find the db in /var/lib/virtuoso/db !
# check output for errors and FIX THEM! (e.g., install missing packages)
make -j5

This will take about 1 hour. In parallel, you might want to start with downloading the DBpedia files (next section) and come back.

sudo make install

Now change the following values in /var/lib/virtuoso/db/virtuoso.ini, the performance tuning stuff is according to

# note: virtuoso ignores lines starting with whitespace
# you need to include the directory where your datasets will be downloaded
# to, in our case /usr/local/data/datasets:
DirsAllowed = ., /usr/share/virtuoso/vad, /usr/local/data/datasets
# IMPORTANT: for performance also do this
# the following two are as suggested by comments in the original .ini
# file in order to use the RAM on your server:
NumberOfBuffers = 2720000
MaxDirtyBuffers = 2000000
# each buffer caches a 8K page of data and occupies approx. 8700 bytes of
# memory. It's suggested to set this value to 65 % of ram for a db only server
# so if you have 32 GB of ram: 32*1000^3*0.65/8700 = 2390804
# default is 2000 which will use 16 MB ram ;)
# Make sure to remove whitespace if you uncomment existing lines!
MaxCheckpointRemap = 625000
# set this to 1/4th of NumberOfBuffers
# I like to increase the ResultSetMaxrows, MaxQueryCostEstimationTime
# and MaxQueryExecutionTime drastically as it's a local store where we
# do quite complex queries... up to you (don't do this if a lot of people
# use it).
# In any case for the importer to be more robust add the following setting
# to this section:
ShortenLongURIs = 1

The next step installs an init-script (autostarts) and starts the virtuoso server. (If you’ve changed directories to edit /var/lib/virtuoso/db/virtuoso.ini, go back to the virtuoso source dir!):

sudo cp debian/init.d /etc/init.d/virtuoso-opensource &&
sudo chmod a+x /etc/init.d/virtuoso-opensource &&
sudo bash debian/virtuoso-opensource.postinst.debhelper

Downloading the DBpedia dump files and a word about problems / inconsistencies in them

The DBpedia 3.7 is split into two separate datasets: one standard version and one i18n version. The standard version mints URIs by going through all English Wikipedia articles. For all of these the cross-language links are used to extract corresponding labels for the en URIs. This is problematic as for example articles which are only in the German Wikipedia won’t be extracted. To solve this problem the i18n version exists and creates IRIs in the form of for every article in the German Wikipedia. There also are interlinking datasets providing owl:sameAs between the new URIs and the ones in corresponding other datasets. Note that the i18n IDs for concepts are IRIs, while the ones in the English Wikipedia are URIs. Also even though the i18n dataset includes all languages, only the Greek (el), German (de) and Russian (ru) Wikipedia have minted their own IRIs. The others are broken… they use URIs start with but are linked to their corresponding language codes in the interlanguage links (e.g., the French interlanguage links falsely point to ). So it’s a mess! If you have a cleaned version of the datasets let us know or just wait for DBpedia 3.8 as we all do 😉

Besides that, the el, de and ru i18n files ending in .nt.gz are actually not valid NT files, because the IRIs are UTF-8 encoded. After finding this out I simply renamed all the German files to .n3.gz. and as n3 is a subset of turtle (TTL) and as virtuoso actually uses a TTL-parser (also for NT which is a subset of n3), I guess that renaming wasn’t all that important for Virtuoso. Still I had a bad feeling of having files with wrong endings flying around.

We have decided that we only needed the German and English files in (NT) format. If you need something different do so (and maybe report back if there were problems and how you solved them). If you decide to download the all-languages tar then make sure to exclude the NQ files from the later importing steps. One simple way to do this is to move everything you don’t want to import out of the directory. Also don’t forget to import the dbpedia_3.*.owl file (last step in the script below)!
Another hint: Virtuoso can only import plain (uncompressed) or gzipped files, the DBpedia dumps are bzipped, so you either repack them into gzip format or extract them. On our server the importing procedure was reasonably slower from extracted files than from gzipped ones (ignoring the vast amount of wasted disk space for the extracted files). File access becomes a bottleneck if you have 4 cores idling. This is why I decided on repacking all the files from bz2 to gz. As you can see I do the en and de repacking in parallel, if that’s not suitable for you, feel free to change it. You might also want to change this if you want to do it in parallel to downloading. The repackaging process below took about 1 hour but was worth it in the end. The more CPUs you have, the more you can parallelize this process.

sudo -i # get root
# see comment above, you could also get the all_language.tar or another DBpedia version...
mkdir -p /usr/local/data/datasets/dbpedia/3.7/3.7/en
cd /usr/local/data/datasets/dbpedia/3.7/3.7/en
wget -r -np -nd -nc -A'*.nt.bz2'

# if you want to save space do this:
for i in *.bz2 ; do bzcat $i | gzip > ${i%.bz2}.gz && rm $i ; done &
# else do:
#bunzip2 *&

cd ..

mkdir ../3.7-i18n/de && cd ../3.7-i18n/de
wget -r -np -nd -nc -A'*.nt.bz2'
# if you want to save space do this:
for i in *.nt.bz2 ; do bzcat $i | gzip > ${i%.nt.bz2}.n3.gz && rm $i ; done &
# else do:
#bunzip2 *

# notice that the extraction (and repacking) of *.bz2 takes quite a while (about 1 hour)
# gzipped data is reasonably packed, but still very fast to access (in contrast to bz2), so maybe this is the best choice.

Data Cleaning and The bulk loader scripts

In contrast to the previous version of this article the virtuoso import will take care of shortening too long IRIs itself. Also it seems the bulk loader script is included in the more recent Virtuoso versions, so as a reference only: see the old version for the cleaning script and VirtBulkRDFLoaderExampleDbpedia and
for info about the bulk loader scripts.

Importing DBpedia dumps into virtuoso

Now AFTER the re-/unpacking of the DBpedia dumps we will register all files in the dbpedia dir (recursively ld_dir_all) to be added to the dbpedia graph. As mentioned above: If you use this method make sure that only files reside in the given subtree that you really want to import.
If you only want one directory’s files to be added (non recursive) use ld_dir.
If you manually want to add some files, use ld_add.
See the VirtBulkRDFLoaderScript file for args to pass.

Be warned that it might be a bad idea to import the normal and i18n dataset into one graph if you didn’t select specific languages, as it might introduce a lot of duplicates. In order to keep track what was selected and imported into which graph (see Note 2 below), we linked (ln -s) the files from the English (orig) and German (i18n) into a directory structure beneath /usr/local/data/datasets/dbpedia/3.7/importedGraphs/ and imported from there instead. To make sure you think about this, I use that path below, so it won’t work if you didn’t pay attention. If you really want, just import /usr/local/data/datasets/dbpedia/3.7/.

Note: in the following i will assume that your virtuoso isql command is called isql. If you’re in lack of such a command it might be called isql-vt.
Note2: in our case we actually decided not to import all the files into just one graph but instead used separated graphs for en and de as well as for the pagelinks, infoboxprops, extlinks and interlanguage_links dumps. Be warned though that only a certain amount of triples from the graph will be shown in case you visit the local pages with your browser.

isql # enter virtuoso sql mode
-- we are in sql mode now
ld_dir_all('/usr/local/data/datasets/dbpedia/3.7/importedGraphs/', '*.*', '');
-- do the following to see which files were registered to be added:
-- if unsatisfied use:
-- delete from DB.DBA.LOAD_LIST;

OK, now comes the fun (and long part: about 7 hours)… We registered the files to be added, now let’s finally start the process. Fire up screen (see comment) if you didn’t already.

sudo aptitude install screen
screen isql
-- (I had some warnings about a possibly corrupt db in the log,
-- when I visited the virtuoso conducter during the first run...)
-- you can watch the progress from another isql session with:
-- select * from DB.DBA.LOAD_LIST;
-- if you need to stop the loading for any reason: rdf_load_stop ();
-- if you want to force stopping: rdf_load_stop(1);
commit WORK;

After this:
Take a look into var/lib/virtuoso/db/virtuoso.log file. Should you find any errors in there… FIX THEM! You might use the dump, but it’s incomplete then. Any error quits out of the loading of the corresponding file and continues with the next one, so you’re only using the part of that file up to the place where the error occurred. (Should you find errors you can’t fix in the way I did above, please leave a comment.)

Final polishing

You can & should now install the DBpedia and RDF Mappers packages from the Virtuoso Conductor.

login: dba
pw: dba

Go to System Admin / Packages. Install the dbpedia and rdf_mappers packages (takes about 5 minutes).

Testing your local mirror

Go to the sparql-endpoint of your server http://your-server:8890/sparql (or in isql prefix with: SPARQL)

SELECT COUNT(*) WHERE { ?s ?p ?o } ;

This might take about 15 minutes and then returns 437,768,995. Subsequent queries are a lot faster (if you find another way (preferably automatic) to warm up the caches, please leave me a note).
I also like this query showing all the graphs and how many triples are in them:

SELECT ?g COUNT(*) { GRAPH ?g {?s ?p ?o.} } GROUP BY ?g ORDER BY DESC 2;
g                                                          callret-1
LONG VARCHAR                                               LONG VARCHAR
___________________________________________________________                                         131477215                               118039661                    83705116                            41397135                                31354613                                      19748791                 11076144                   694064 256065
http://localhost:8890/DAV                                  4009                 2066                                1480                             1226                           937                                  857                804               696              691                       661
virtrdf-label                                              638                 613                                 557                                   553                     482               426               386                           332                   311                        252                     225                    183                  172                             167                              160                   144                   143                           139                        117                  103           102                    90                      87                85                     79              68                      41                  26                    23       21                    21                  12
dbprdf-label                                               6

52 ROWS. -- 1711753 msec.

Congratulations, you just imported nearly half a billion triples.

Backing up this initial state

Now is a good moment to backup the whole db (takes about half an hour):

sudo -i
cd /
/etc/init.d/virtuoso-opensource stop &&
tar -cvf - /var/lib/virtuoso | gzip --fast > virtuoso-6.1.6-dev-DBDUMP-dbpedia-3.7-en_de-$(date '+%F').tar.gz &&
/etc/init.d/virtuoso-opensource start

Yay, done 😉
As always, feel free to leave comments to tell us about your problems or how happy you are :D.


Many thanks to the DBpedia team for their endless efforts of providing us all with a great dataset. Also many thanks to the Virtuoso crew for releasing an opensource version of their DB; especially to Hugh Williams and Patrick van Kleef for helping me out with a couple of problems in the newer version.