<s>
The	O
Hierarchy	B-Architecture
Open	I-Architecture
Service	I-Architecture
Interface	I-Architecture
Definition	I-Architecture
(	O
OSID	B-Architecture
)	O
is	O
an	O
Open	O
Knowledge	O
Initiative	O
specification	O
.	O
</s>
<s>
OSIDs	B-Architecture
are	O
programmatic	O
interfaces	O
which	O
comprise	O
a	O
Service	O
Oriented	O
Architecture	O
for	O
designing	O
and	O
building	O
reusable	B-Application
and	O
interoperable	O
software	O
.	O
</s>
<s>
The	O
Hierarchy	B-Architecture
OSID	I-Architecture
which	O
provides	O
a	O
means	O
of	O
creating	O
and	O
traversing	O
hierarchical	O
structures	O
of	O
various	O
types	O
.	O
</s>
<s>
These	O
types	O
include	O
trees	B-Application
,	O
forests	O
,	O
directed	O
graphs	O
with	O
multiple	O
parents	O
,	O
and	O
directed	O
acyclic	O
graphs	O
.	O
</s>
<s>
The	O
Hierarchy	B-Architecture
OSID	I-Architecture
creates	O
a	O
common	O
tools	O
for	O
viewing	O
and	O
maintaining	O
this	O
type	O
of	O
structure	O
.	O
</s>
<s>
While	O
these	O
data	O
collections	O
have	O
rich	O
structures	O
themselves	O
,	O
the	O
Hierarchy	B-Architecture
OSID	I-Architecture
is	O
concerned	O
only	O
with	O
the	O
hierarchical	O
relationship	O
among	O
nodes	O
and	O
not	O
what	O
the	O
nodes	O
represent	O
.	O
</s>
