问题

我正在编写一个在家庭关系上操作的[Souffle](https://souffle-lang.github.io/)查询：

.decl Parent(x: symbol, y: symbol)
.input Parent

.decl Descendant(x: symbol, y: symbol)
.output Descendant
.printsize Descendant

Descendant(x, y) :- Parent(x, y).
Descendant(x, y) :- Parent(z, y), Descendant(x, z).

.decl Qslow(x: symbol)
.output Qslow
.printsize Qslow

Qslow(x) :- Descendant("Alice", x).

我有一些事实在一个TSV文件`Parent.facts`中：

"Alice" "john"
"john" "mary"
"mary" "elizabeth"
"Bob" "charles"

运行`souffle`似乎为`Descendant`关系生成了正确的输出（对于"Alice"有三个后代）：

hickory% souffle -F. -D. descendants.dl
Descendant 7
Qslow 0
hickory%

然而，`Qslow`产生了**零**结果。我本来希望有**三**个结果。这让我怀疑`Qslow`的定义，但我不确定问题是什么。我是否在符号语法上做了一些奇怪的事情？看起来我使用的语法与[文档中的](https://souffle-lang.github.io/types#float-type)相同。

如果我尝试在连接中添加另一个子句，仍然会得到零结果：

Qslow(x) :- Descendant(y, x), y="Alice".

<details>
<summary>英文:</summary>

I am writing a [Souffle](https://souffle-lang.github.io/) query that operates on family relationships:

.decl Parent(x: symbol, y: symbol)
.input Parent

.decl Descendant(x: symbol, y: symbol)
.output Descendant
.printsize Descendant

Descendant(x, y) :- Parent(x, y).
Descendant(x, y) :- Parent(z, y), Descendant(x, z).

.decl Qslow(x: symbol)
.output Qslow
.printsize Qslow

Qslow(x) :- Descendant("Alice", x).

I have some facts in a TSV file `Parent.facts`:

"Alice" "john"
"john" "mary"
"mary" "elizabeth"
"Bob" "charles"

And running `souffle` seems to generate the right output for the `Descendant` relation (three descendants for "Alice"):

hickory% souffle -F. -D. descendants.dl
Descendant 7
Qslow 0
hickory%

However, `Qslow` produces **zero** results. I would instead expect **three** results. This makes me suspicious of the definition of `Qslow`, but I am not sure what the issue is. Am I doing something weird with symbol syntax? It looks like I am using the same syntax as [in the docs](https://souffle-lang.github.io/types#float-type).

If I try adding another clause to the conjunction, I still get zero results:

Qslow(x) :- Descendant(y, x), y="Alice".

</details>


# 答案1
**得分**: 2

您已经在错误的数据格式中指定了文件 `Parent.facts`。它应该是

```Alice	john
john	mary
mary	elizabeth
Bob	charles

不带双引号，并且使用制表符来分隔元组的元素。程序中只有事实使用双引号。

john	mary
mary	elizabeth
Bob	charles