`has` statement

The statement <OWNER VAR> has <ATTRIBUTE VAR> is used to identify the <OWNER VAR> as owning the <ATTRIBUTE VAR>.

Schema for the following examples

#!test[schema]
define
attribute name, value string;
entity person, owns name;

Inserting attribute ownership

The has keyword can be used to attach an attribute to an object.

#!test[write]
#{{
match $person isa person; $name isa name;
#}}
insert $person has $name;

An attribute can be created in-place by providing its type and value.

#!test[write]
#{{
match $person isa person;
#}}
insert $person has name "Alice";

The has keyword is used to remove an attribute from its owner.

#!test[write]
#{{
match $person isa person, has name $name;
#}}
delete has $name of $person;

The has keyword can be used to match attributes of an object.

#!test[read]
match $person has $name;

The attribute type may be provided.

#!test[read]
match $person has name $name;

The attribute can be matched by attribute type and value instead of binding it to a variable.

#!test[read]
match $person has name "Alice";

Alternatively, a comparison can be used to constrain the attribute value.

#!test[read]
match $person has name < "Bob";