<s>
Document	B-General_Concept
Definition	I-General_Concept
Markup	I-General_Concept
Language	I-General_Concept
(	O
DDML	B-General_Concept
)	O
is	O
an	O
XML	B-Language
schema	I-Language
language	O
proposed	O
in	O
1999	O
by	O
various	O
contributors	O
from	O
the	O
xml-dev	O
electronic	O
mailing	O
list	O
.	O
</s>
<s>
DDML	B-General_Concept
began	O
as	O
XSchema	O
,	O
a	O
reformulation	O
of	O
XML	B-Language
DTDs	I-Language
as	O
full	O
XML	O
documents	O
,	O
so	O
that	O
elements	O
and	O
attributes	O
,	O
rather	O
than	O
declarations	O
,	O
could	O
be	O
used	O
to	O
describe	O
a	O
schema	O
.	O
</s>
<s>
As	O
development	O
continued	O
,	O
the	O
name	O
was	O
changed	O
to	O
DDML	B-General_Concept
,	O
reflecting	O
a	O
shift	O
away	O
from	O
the	O
goal	O
of	O
replicating	O
all	O
DTD	B-Language
functionality	O
,	O
in	O
order	O
to	O
concentrate	O
on	O
providing	O
a	O
robust	O
framework	O
for	O
describing	O
basic	O
element/attribute	O
hierarchy	O
.	O
</s>
<s>
DDML	B-General_Concept
offered	O
no	O
datatypes	O
or	O
functionality	O
beyond	O
what	O
DTDs	O
already	O
provided	O
,	O
so	O
there	O
was	O
not	O
much	O
advantage	O
to	O
using	O
DDML	B-General_Concept
instead	O
of	O
DTDs	O
.	O
</s>
<s>
DDML	B-General_Concept
did	O
,	O
however	O
,	O
inform	O
the	O
development	O
of	O
the	O
next	O
generation	O
of	O
XML-based	O
schema	O
languages	O
,	O
including	O
the	O
more	O
successful	O
XML	B-Language
Schema	I-Language
and	O
RELAX	B-Language
NG	I-Language
.	O
</s>
