<s>
Rel	B-Application
is	O
an	O
open-source	B-Application
true	O
relational	B-Application
database	I-Application
management	I-Application
system	I-Application
that	O
implements	O
a	O
significant	O
portion	O
of	O
Chris	O
Date	O
and	O
Hugh	O
Darwen	O
's	O
Tutorial	O
D	O
query	B-Language
language	I-Language
.	O
</s>
<s>
Primarily	O
intended	O
for	O
teaching	O
purposes	O
,	O
Rel	B-Application
is	O
written	O
in	O
the	O
Java	B-Language
programming	I-Language
language	I-Language
.	O
</s>
