<s>
The	O
Vadalog	B-Language
system	O
is	O
a	O
Knowledge	B-Application
Graph	I-Application
Management	O
System	O
(	O
KGMS	O
)	O
that	O
offers	O
a	O
language	O
for	O
performing	O
complex	O
logic	B-Language
reasoning	O
tasks	O
over	O
knowledge	B-Application
graphs	I-Application
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
Vadalog	B-Language
delivers	O
a	O
platform	O
to	O
support	O
the	O
entire	O
spectrum	O
of	O
data	O
science	O
tasks	O
:	O
data	B-General_Concept
integration	I-General_Concept
,	O
pre-processing	O
,	O
statistical	O
analysis	O
,	O
machine	O
learning	O
,	O
algorithmic	O
modeling	O
,	O
probabilistic	O
reasoning	O
and	O
temporal	O
reasoning	O
.	O
</s>
<s>
Its	O
language	O
is	O
based	O
on	O
an	O
extension	O
of	O
the	O
rule-based	B-Language
language	O
Datalog	B-Language
,	O
Warded	O
Datalog±	O
,	O
a	O
high-performance	O
language	O
using	O
an	O
aggressive	O
termination	O
control	O
strategy	O
.	O
</s>
<s>
Vadalog	B-Language
can	O
support	O
the	O
entire	O
spectrum	O
of	O
data	O
science	O
activities	O
and	O
tools	O
.	O
</s>
<s>
The	O
system	O
can	O
read	O
from	O
and	O
connect	O
to	O
multiple	O
sources	O
,	O
from	O
relational	O
databases	O
,	O
such	O
as	O
PostgreSQL	B-Application
and	O
MySQL	B-Application
,	O
to	O
graph	B-Application
databases	I-Application
,	O
such	O
as	O
Neo4j	B-Language
,	O
as	O
well	O
as	O
make	O
use	O
of	O
machine	O
learning	O
tools	O
(	O
e.g.	O
,	O
Weka	B-Language
and	O
scikit-learn	B-Application
)	O
,	O
and	O
a	O
web	O
data	O
extraction	O
tool	O
,	O
OXPath	O
.	O
</s>
<s>
Vadalog	B-Language
is	O
the	O
result	O
of	O
a	O
joint	O
effort	O
between	O
University	O
of	O
Oxford	O
,	O
the	O
Knowledge	B-Application
Graph	I-Application
Lab	O
of	O
Technische	O
Universität	O
Wien	O
and	O
Bank	O
of	O
Italy	O
.	O
</s>
<s>
A	O
knowledge	B-Application
graph	I-Application
management	O
system	O
(	O
KGMS	O
)	O
has	O
to	O
manage	O
knowledge	B-Application
graphs	I-Application
,	O
which	O
incorporate	O
large	O
amounts	O
of	O
data	O
in	O
the	O
form	O
of	O
facts	O
and	O
relationships	O
.	O
</s>
<s>
Big	O
Data	O
,	O
which	O
is	O
the	O
need	O
of	O
handling	O
large	O
amounts	O
of	O
data	O
,	O
especially	O
when	O
considering	O
that	O
knowledge	B-Application
graphs	I-Application
have	O
been	O
thought	O
as	O
a	O
solution	O
for	O
integrating	O
multiple	O
data	O
sources	O
,	O
both	O
corporate	O
and	O
public	O
knowledge	O
,	O
which	O
can	O
be	O
integrated	O
into	O
large	O
knowledge	B-Application
graphs	I-Application
,	O
</s>
<s>
definition	O
of	O
a	O
language	O
and	O
a	O
formalism	O
with	O
high	O
expressive	B-Language
power	I-Language
,	O
</s>
<s>
cost-effective	O
data	B-General_Concept
wrangling	I-General_Concept
,	O
in	O
all	O
its	O
steps	O
,	O
from	O
data	O
cleaning	O
to	O
web	O
data	O
extraction	O
and	O
big	O
data	O
access	O
from	O
many	O
different	O
sources	O
,	O
</s>
<s>
interfaces	O
(	O
APIs	B-Application
)	O
to	O
access	O
many	O
heterogeneous	O
data	O
sources	O
,	O
such	O
as	O
corporate	O
RDBMS	O
,	O
NoSQL	B-General_Concept
or	O
RDF	O
stores	O
,	O
the	O
web	O
,	O
machine-learning	O
and	O
analytics	O
packages	O
.	O
</s>
<s>
Other	O
requirements	O
may	O
include	O
more	O
typical	O
DBMS	B-General_Concept
functions	O
and	O
services	O
,	O
as	O
the	O
ones	O
proposed	O
by	O
Codd	O
.	O
</s>
<s>
Vadalog	B-Language
offers	O
a	O
platform	O
that	O
fulfills	O
all	O
the	O
requirements	O
of	O
a	O
KGMS	O
listed	O
above	O
.	O
</s>
<s>
It	O
is	O
able	O
to	O
perform	O
rule-based	B-Language
reasoning	O
tasks	O
on	O
top	O
of	O
knowledge	B-Application
graphs	I-Application
and	O
it	O
also	O
supports	O
the	O
data	O
science	O
workflow	O
,	O
such	O
as	O
data	O
visualization	O
and	O
machine	O
learning	O
.	O
</s>
<s>
The	O
most	O
widespread	O
form	O
of	O
knowledge	O
that	O
has	O
been	O
adopted	O
over	O
the	O
last	O
decades	O
has	O
been	O
in	O
the	O
form	O
of	O
rules	O
,	O
be	O
it	O
in	O
rule-based	B-Language
systems	O
,	O
ontology-based	O
systems	O
or	O
other	O
forms	O
and	O
it	O
can	O
be	O
typically	O
captured	O
in	O
knowledge	B-Application
graphs	I-Application
.	O
</s>
<s>
The	O
nature	O
of	O
knowledge	B-Application
graphs	I-Application
also	O
makes	O
the	O
presence	O
of	O
recursion	O
in	O
these	O
rules	O
a	O
particularly	O
important	O
aspect	O
.	O
</s>
<s>
The	O
Vadalog	B-Language
language	O
allows	O
to	O
answer	O
reasoning	O
queries	O
that	O
also	O
include	O
recursion	O
.	O
</s>
<s>
It	O
is	O
based	O
on	O
Warded	O
Datalog±	O
,	O
which	O
belongs	O
to	O
the	O
Datalog±	O
family	O
of	O
languages	O
that	O
extends	O
Datalog	B-Language
with	O
existential	B-Algorithm
quantifiers	I-Algorithm
in	O
rule	O
heads	O
and	O
at	O
the	O
same	O
time	O
restricts	O
its	O
syntax	O
in	O
order	O
to	O
achieve	O
decidability	O
and	O
tractability	O
.	O
</s>
<s>
or	O
,	O
alternatively	O
,	O
in	O
Datalog	B-Language
syntax	O
,	O
it	O
can	O
be	O
written	O
as	O
follows:Variables	O
in	O
Vadalog	B-Language
are	O
like	O
variables	O
in	O
first-order	O
logic	B-Language
and	O
a	O
variable	O
is	O
local	O
to	O
the	O
rule	O
in	O
which	O
it	O
occurs	O
.	O
</s>
<s>
Warded	O
Datalog±	O
overcomes	O
this	O
issue	O
asking	O
that	O
for	O
every	O
rule	O
defined	O
in	O
a	O
set	O
,	O
all	O
the	O
variables	O
in	O
the	O
rule	O
bodies	O
must	O
coexist	O
in	O
at	O
least	O
one	O
atom	O
in	O
the	O
head	O
,	O
called	O
a	O
ward	O
.	O
</s>
<s>
Although	O
this	O
is	O
a	O
limit	O
in	O
terms	O
of	O
expressive	B-Language
power	I-Language
,	O
with	O
this	O
requirement	O
and	O
thanks	O
to	O
its	O
architecture	O
and	O
termination	O
algorithms	O
,	O
Warded	O
Datalog±	O
is	O
able	O
to	O
find	O
answers	O
to	O
a	O
program	O
in	O
a	O
finite	O
number	O
of	O
steps	O
.	O
</s>
<s>
It	O
also	O
exhibits	O
a	O
good	O
trade-off	O
between	O
computational	O
complexity	O
and	O
expressive	B-Language
power	I-Language
,	O
capturing	O
PTIME	O
data	O
complexity	O
while	O
allowing	O
ontological	O
reasoning	O
and	O
the	O
possibility	O
of	O
running	O
programs	O
with	O
recursion	O
.	O
</s>
<s>
Vadalog	B-Language
replicates	O
in	O
its	O
entirety	O
Warded	O
Datalog±	O
and	O
extends	O
it	O
with	O
the	O
inclusion	O
in	O
the	O
language	O
of	O
:	O
</s>
<s>
Adopting	O
an	O
in-memory	B-General_Concept
processing	I-General_Concept
architecture	O
and	O
a	O
pull	O
stream-based	B-Operating_System
approach	O
,	O
which	O
limits	O
the	O
memory	O
consumption	O
or	O
make	O
it	O
predictable	O
.	O
</s>
<s>
The	O
Vadalog	B-Language
system	O
is	O
therefore	O
able	O
to	O
perform	O
ontological	O
reasoning	O
tasks	O
,	O
as	O
it	O
belongs	O
to	O
the	O
Datalog	B-Language
family	O
.	O
</s>
<s>
Reasoning	O
with	O
the	O
logical	O
core	O
of	O
Vadalog	B-Language
captures	O
OWL	B-Language
2	I-Language
QL	I-Language
and	O
SPARQL	B-Language
(	O
through	O
the	O
use	O
of	O
existential	B-Algorithm
quantifiers	I-Algorithm
)	O
,	O
and	O
graph	O
analytics	O
(	O
through	O
support	O
for	O
recursion	O
and	O
aggregation	O
)	O
.	O
</s>
<s>
The	O
declarative	B-Language
nature	O
of	O
the	O
language	O
makes	O
the	O
code	O
easy-to-read	O
and	O
manageable	O
.	O
</s>
<s>
Consider	O
the	O
following	O
set	O
of	O
Vadalog	B-Language
rules:ancestor(Y,X )	O
:	O
-	O
person(X )	O
.	O
</s>
<s>
ancestor(Y,Z )	O
:	O
-	O
ancestor(Y,X )	O
,	O
parent(X,Z )	O
.The	O
first	O
rule	O
states	O
that	O
for	O
each	O
person	O
there	B-Algorithm
exists	I-Algorithm
an	O
ancestor	O
.	O
</s>
<s>
Note	O
the	O
existential	B-Algorithm
quantification	I-Algorithm
in	O
the	O
first	O
position	O
of	O
the	O
ancestor	O
predicate	O
in	O
the	O
first	O
rule	O
,	O
which	O
will	O
generate	O
a	O
null	O
νi	O
in	O
the	O
chase	O
procedure	O
.	O
</s>
<s>
The	O
integration	O
of	O
Vadalog	B-Language
with	O
data	O
science	O
tools	O
is	O
achieved	O
by	O
means	O
of	O
data	B-General_Concept
bindings	I-General_Concept
primitives	I-General_Concept
and	O
functions	O
.	O
</s>
<s>
Data	B-General_Concept
binding	I-General_Concept
primitives	O
:	O
bindings	O
allow	O
to	O
connect	O
to	O
external	O
data	O
sources	O
or	O
systems	O
like	O
a	O
database	O
,	O
a	O
framework	O
or	O
a	O
library	O
and	O
tell	O
the	O
system	O
how	O
to	O
deal	O
with	O
them	O
.	O
</s>
<s>
This	O
includes	O
connections	O
with	O
relational	O
database	O
systems	O
as	O
PostgreSQL	B-Application
or	O
MySQL	B-Application
,	O
and	O
graph	B-Application
databases	I-Application
,	O
such	O
as	O
Neo4j	B-Language
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
integrate	O
machine	O
learning	O
libraries	O
(	O
Weka	B-Language
,	O
scikit-learn	B-Application
,	O
Tensorflow	B-Language
)	O
and	O
a	O
web	O
data	O
extraction	O
tool	O
,	O
OXPath	O
,	O
which	O
allows	O
to	O
retrieve	O
data	O
directly	O
from	O
the	O
web	O
.	O
</s>
<s>
The	O
system	O
also	O
provides	O
an	O
integration	O
with	O
the	O
JupyterLab	O
platform	O
,	O
where	O
Vadalog	B-Language
programs	O
can	O
be	O
written	O
and	O
run	O
and	O
the	O
output	O
can	O
be	O
read	O
,	O
exploiting	O
the	O
functionalities	O
of	O
the	O
platform	O
.	O
</s>
<s>
It	O
gives	O
also	O
the	O
possibility	O
to	O
evaluate	O
the	O
correctness	O
of	O
the	O
program	O
,	O
run	O
it	O
and	O
analyse	O
the	O
derivation	O
process	O
of	O
output	O
facts	O
by	O
means	O
of	O
tools	O
as	O
syntax	O
highlighting	O
,	O
code	O
analysis	O
(	O
checking	O
whether	O
the	O
code	O
is	O
correct	O
or	O
there	O
are	O
errors	O
)	O
and	O
explanations	O
of	O
results	O
(	O
how	O
the	O
result	O
has	O
been	O
obtained	O
)	O
:	O
all	O
these	O
functionalities	O
are	O
embedded	O
in	O
the	O
notebook	O
and	O
help	O
in	O
writing	O
and	O
analyzing	O
Vadalog	B-Language
code	O
.	O
</s>
<s>
The	O
Vadalog	B-Language
system	O
can	O
be	O
employed	O
to	O
address	O
many	O
real-world	O
use	O
cases	O
from	O
distinct	O
research	O
and	O
industry	O
fields	O
.	O
</s>
<s>
These	O
rules	O
can	O
be	O
written	O
in	O
a	O
Vadalog	B-Language
program	O
that	O
will	O
derive	O
all	O
control	O
edges	O
like	O
the	O
following:control(X,X )	O
:	O
-	O
company(X )	O
.	O
</s>
<s>
This	O
scenario	O
consists	O
in	O
determining	O
whether	O
there	B-Algorithm
exists	I-Algorithm
a	O
link	O
between	O
two	O
entities	O
in	O
a	O
company	O
ownerships	O
graph	O
.	O
</s>
<s>
These	O
rules	O
can	O
be	O
written	O
in	O
a	O
Vadalog	B-Language
program	O
that	O
will	O
derive	O
all	O
close	O
link''	O
edges	O
like	O
the	O
following:The	O
first	O
rule	O
states	O
that	O
two	O
companies	O
and	O
connected	O
by	O
an	O
ownership	O
edge	O
are	O
possible	O
close	O
links	O
.	O
</s>
<s>
The	O
second	O
rule	O
states	O
that	O
,	O
if	O
and	O
are	O
possible	O
close	O
links	O
with	O
a	O
share	O
and	O
there	B-Algorithm
exists	I-Algorithm
an	O
ownership	O
edge	O
from	O
to	O
a	O
company	O
with	O
a	O
share	O
,	O
then	O
also	O
and	O
are	O
possible	O
close	O
links	O
with	O
a	O
share	O
.	O
</s>
