Grakn中出现“规则图不可分层”错误

Question

我正在尝试插入此规则(数据被屏蔽)：

when {
    $d isa person; 
    $a isa animal; 
    $r (role-1: $d, role-2: $a) isa relation-1, has attr $ds; 
    not {$r1 (role-3: $d, role-4: $a) isa relation-2; };
    $ds > 0.5;
}, then {
    (role-3: $a, role-4: $d, role-5: $ds) isa relation-2;
};

然而，在我执行commit之后，我一直收到这个结构验证错误。请帮帮忙

INVALID_ARGUMENT: InvalidKBException-A structural validation error has occurred. Please correct the [`1`] errors found. 
The rule graph is not stratifiable - it contains following cycles with negation: [[[Base Type [RELATION_TYPE] - Id [V65648]  - Label [relation-2] ]]]
. Please check server logs for the stack trace.
All uncommitted data is cleared

Answer 1

在Grakn中不允许出现导致循环的规则-例如，在when子句中否定结论。

这里有一个例子来说明原因。

define
person sub entity, plays employee;
employment sub relation, relates employee;

there-are-no-unemployed sub rule,
when {
    $p isa person;
    not {
        (employee: $p) isa employment;
    };
}, then {
    (employee: $p) isa employment;
}

如果我们有一个人不在employment关系中，那么他们就是在employment关系中。但现在，我们已经反驳了规则的最初前提-它们不在employment关系中。因此，我们有一个逻辑上的矛盾。