I am looking for some external feedback regarding the OSGi filter
syntax. We are investigating if we should address some of the
shortcomings in R5 or if this is not worth the required version
change.
The OSGi filter syntax is compatible with the LDAP filter syntax. This
syntax has a few shortcomings that we inherited. For example, the
syntax does not have operators for more (>) and less (<). There are
work arounds for this because >= and <= as well as not (!) are
supported.
(a>b) <=> (!(a<=b))
Today there is very little reason to not add these operators to the
filter, it is likely to safe newcomers a few hours. The change is
backward compatible but not forward compatible. Newer bundles that
will use the new syntax will not run on older frameworks.
If we decide add the > and < operators, we could afford to add more
operators. The filter is used in many different places and a more
powerful syntax would have its value. This mail is trying to start a
discussion what kind of operators could be added.
!= not equal
Additionally, we should consider adding regular expressions. Regular
expressions are extremely powerful and play a major role in most
mainstream languages like perl and php. We could consider using the /
operator for regular expressions:
/ regular expression (requires java.util.regex)
Working on OBR, I found I needed set operators: subset and superset:
*> super set ( key *> {1,2,3} : the value of key, an array or
collection must contain at least 1,2,3
<* subset ( key <* {1,2,3} : key (which is a Collection or array)
must contain at most 1,2,3 )
The exact syntax and escaping needs to be worked upon.
During initial discussion on the CPEG call the idea was brought up to
create an extension model for the filter. This would allow third
parties to add operators. I am not fond of this idea because it makes
the presence of operators very fuzzy, it is hard to get popular
operators when the presence of the operator depends on other installed
bundles.
Kind regards,
Peter Kriens
--
Peter Kriens Tel +33467542167
9C, Avenue St. Drézéry AOL,Yahoo: pkriens
34160 Beaulieu, France ICQ 255570717
Skype pkriens Fax +1 8153772599
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