15
Single Type SDTDs
•
One more restriction: if E’ contains two
occurrences of
s
2
S
, then they have the
same “type”.
–
Formally: there are no two occurrences of
s
1
’
and
s
2
’ in any regular expression E’ s.t.
m
(
s
1
’)
=
m
(
s
2
’)
•
The XML Schema standard has such a
requirement