<s>
Database	B-General_Concept
theory	I-General_Concept
encapsulates	O
a	O
broad	O
range	O
of	O
topics	O
related	O
to	O
the	O
study	O
and	O
research	O
of	O
the	O
theoretical	O
realm	O
of	O
databases	O
and	O
database	O
management	O
systems	O
.	O
</s>
<s>
Theoretical	O
aspects	O
of	O
data	O
management	O
include	O
,	O
among	O
other	O
areas	O
,	O
the	O
foundations	O
of	O
query	O
languages	O
,	O
computational	O
complexity	O
and	O
expressive	B-Language
power	I-Language
of	O
queries	O
,	O
finite	O
model	O
theory	O
,	O
database	B-General_Concept
design	I-General_Concept
theory	O
,	O
dependency	O
theory	O
,	O
foundations	O
of	O
concurrency	B-Operating_System
control	I-Operating_System
and	O
database	O
recovery	O
,	O
deductive	B-General_Concept
databases	I-General_Concept
,	O
temporal	O
and	O
spatial	B-Algorithm
databases	I-Algorithm
,	O
real-time	B-Application
databases	I-Application
,	O
managing	O
uncertain	B-Algorithm
data	I-Algorithm
and	O
probabilistic	B-General_Concept
databases	I-General_Concept
,	O
and	O
Web	O
data	O
.	O
</s>
<s>
Most	O
research	O
work	O
has	O
traditionally	O
been	O
based	O
on	O
the	O
relational	B-Architecture
model	I-Architecture
,	O
since	O
this	O
model	O
is	O
usually	O
considered	O
the	O
simplest	O
and	O
most	O
foundational	O
model	O
of	O
interest	O
.	O
</s>
<s>
Corresponding	O
results	O
for	O
other	O
data	O
models	O
,	O
such	O
as	O
object-oriented	O
or	O
semi-structured	B-General_Concept
models	I-General_Concept
,	O
or	O
,	O
more	O
recently	O
,	O
graph	O
data	O
models	O
and	O
XML	B-Protocol
,	O
are	O
often	O
derivable	O
from	O
those	O
for	O
the	O
relational	B-Architecture
model	I-Architecture
.	O
</s>
<s>
Database	B-General_Concept
theory	I-General_Concept
helps	O
one	O
to	O
understand	O
the	O
complexity	O
and	O
power	O
of	O
query	O
languages	O
and	O
their	O
connection	O
to	O
logic	O
.	O
</s>
<s>
Starting	O
from	O
relational	B-Algorithm
algebra	I-Algorithm
and	O
first-order	O
logic	O
(	O
which	O
are	O
equivalent	O
by	O
Codd	B-Application
's	I-Application
theorem	I-Application
)	O
and	O
the	O
insight	O
that	O
important	O
queries	O
such	O
as	O
graph	O
reachability	O
are	O
not	O
expressible	O
in	O
this	O
language	O
,	O
more	O
powerful	O
language	O
based	O
on	O
logic	B-Language
programming	I-Language
and	O
fixpoint	O
logic	O
such	O
as	O
datalog	B-Language
were	O
studied	O
.	O
</s>
<s>
The	O
theory	O
also	O
explores	O
foundations	O
of	O
query	B-Language
optimization	I-Language
and	O
data	B-General_Concept
integration	I-General_Concept
.	O
</s>
<s>
Here	O
most	O
work	O
studied	O
conjunctive	O
queries	O
,	O
which	O
admit	O
query	B-Language
optimization	I-Language
even	O
under	O
constraints	O
using	O
the	O
chase	B-Algorithm
algorithm	O
.	O
</s>
<s>
The	O
main	O
research	O
conferences	O
in	O
the	O
area	O
are	O
the	O
ACM	O
Symposium	O
on	O
Principles	O
of	O
Database	O
Systems	O
(	O
PODS	O
)	O
and	O
the	O
International	O
Conference	O
on	O
Database	B-General_Concept
Theory	I-General_Concept
(	O
ICDT	O
)	O
.	O
</s>
