Keywords

Any programming language has its own set of reserved words (keywords) that cannot be used as identifiers. For instance, the keyword ``if'' cannot be used as a variable in a C program.
OQL also has its own set of keywords. But OQL is one part among others in the information system: for instance, there are an Object Model, an Object Definition Language (ODL) and Language bindings. The Object Model does not introduce any keyword, while ODL has its own set of keywords which are different from the OQL keywords. For instance, a class can include an attribute whose name is ``if'' as it is not a ODL keyword. If one wants to access this attribute in OQL, using for instance the path expression ``x.if'', we will get a syntax error. This is not acceptable.
We introduce in OQL (and in ODL) a way to neutralize any keyword: the token ``@'' used as a prefix keyword neutralizes the keyword and makes it a valid identifier. For instance, ``x.@if'', denotes the attribute ``if'' of the instance ``x''.
More generaly, ``@identifier'' denotes the identifier ``identifier'' whether ``identifier'' is a keyword or not.

OQL introduces the following keywords:

add	all	append	array	as
asc	bag	bodyof	break	by
char	classof	contents	define	delete
desc	distinct	do	element	else
empty	eval	except	exists	false
float	for	from	function	group
having	ident	if	import	in
int	intersect	is	isset	like
list	mod	new	nil	not
oid	order	pop	print	push
refof	return	scopeof	select	set
string	struct	structof	suppress	then
throw	to	true	typeof	union
unset	unval	valof	where	while