sparql - SPARQL - 计算对象中子字符串的出现次数

Question

我对链接数据相当陌生，SPARQL但我了解这个概念和一些查询，因为我确实了解 SQL。使用来自 rdfdata.org 的一些示例数据，我设法使用Elvis impersonator repo设置了一个 GraphDB 实例。

使用一些基本查询 SELECT * WHERE {?s ?p ?o}，如对象值过滤，我能够在表中获得一些可见的基本数据。我有使用正则表达式的经验，所以我决定将它与 SPARQL 一起使用来计算Elvis对象中出现的次数。但是，无论我做什么，我都无法得到这个。

这是一个问题，因为我有包含elvis不止一次形式的三元组：

 s: http://www.gigmasters.com/elvis/bobjames/
 p: ep:influences
 o: Elvis Elvis Elvis! I also do a Neil Diamond tribute as well, and have 
     been a DJ, MC, and musician for many years.

如您所见，出现 3 次Elvis仅计为 1。

这是用于选择三元组并计算出现次数的 SPARQL 查询：

SELECT ?s ?p ?o (count(regex( ?o ,"[Ee]lvis")) as ?count)
WHERE {
    ?s ?p ?o.
    filter(regex( ?o ,"([Ee]lvis.){3}")) //only return the triple above
}
GROUP BY ?s ?p ?o

这些事件怎么可能不计算在内？我尝试使用str(?o)但因为该对象是一个以字符串文字开头的字符串，这无关紧要。

预期结果：

具有 4 列的 le 表：| ?s | ?p | ?o | count |，其中 count 应该是"3"^^xsd:integer

Answer 1

您可以通过获取输入字符串（例如，"A B A C"），将出现的目标（例如，"A"）替换为空字符串（""）来获得更新的字符串（例如，" B C"）来完成此操作。然后，计算更新字符串的长度与输入字符串的长度之差。将其除以目标的长度，这就是目标在输入中出现的次数。例如：

@prefix : <urn:ex:>

:a :hasString "I like Elvis." .
:b :hasString "Elvis's name was Elvis." .
:c :hasString "Not mentioned here" .
:d :hasString "daybydaybyday" .

prefix : <urn:ex:>

select ?x ?s ?t ?count where {
  values ?t { "Elvis" "daybyday" }
  ?x :hasString ?s .
  bind(((strlen(?s) - strlen(replace(?s, ?t, ""))) / strlen(?t)) as ?count)
}

-------------------------------------------------------
| x  | s                         | t          | count |
=======================================================
| :a | "I like Elvis."           | "Elvis"    | 1.0   |
| :b | "Elvis's name was Elvis." | "Elvis"    | 2.0   |
| :c | "Not mentioned here"      | "Elvis"    | 0.0   |
| :d | "daybydaybyday"           | "Elvis"    | 0.0   |
| :a | "I like Elvis."           | "daybyday" | 0.0   |
| :b | "Elvis's name was Elvis." | "daybyday" | 0.0   |
| :c | "Not mentioned here"      | "daybyday" | 0.0   |
| :d | "daybydaybyday"           | "daybyday" | 1.0   |
-------------------------------------------------------

这里有几个警告。

• 目标字符串必须是“普通”字符串。例如，如果它是一个真正的正则表达式模式，可以扩展到不同长度的文本，那么这个方法就行不通。
• 您需要了解它如何处理重叠字符串。例如，如果您的输入文本是“daybydaybyday”并且目标是“daybyday”，您希望计算一次还是两次？使用这种方法，您只会得到一个，因为一旦替换了一个匹配项，剩下的字符串就不再存在了。

Answer 2

SPARQL 计数用于计算 RDF 数据中匹配的可能绑定的数量，或者简单地说，匹配的行数。实际上只有一个对象与 REGEX 匹配，因此只有一行。不幸的是，SPARQL 没有任何从单行创建多行的爆炸概念（或者更好地说，我不知道）。

作为一种解决方法，我使用 REGEX + String hacks 编写了一个 SPARQL 查询。这个想法是

1. Elvis用一些希望不会出现的特殊字符替换每次出现的。我选择 Å 在这里进行演示。
2. 删除文本中的其他字符
3. 计算剩余字符串的长度

询问

PREFIX ep: <http://www.snee.com/ns/ep>
SELECT ?s ?p ?o ?cnt
WHERE {

  ?s ?p ?o.
  filter(regex( str(?o) ,"([Ee]lvis.)")) 
  bind(
    strlen(
        replace(
            replace(str(?o), "([Ee]lvis.)", "Å")
            , "[^Å]", ""
        )
    ) as ?cnt) 
}

输出（样本）

+-----------------------------------------------+-------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------+
|                       s                       |                  p                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                               o                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | cnt  |
+-----------------------------------------------+-------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------+
| http://www.gigmasters.com/elvis/ChuckBaril/   | http://www.snee.com/ns/epinfluences | Elvis, Donny Osmond, Barry Manilow, Pebo Bryson, James Ingram, George Benson, and George Strait                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |    1 |
|  http://www.gigmasters.com/elvis/DukeHicks/   |  dc:description                     | Been performing Elvis tribute shows for 10 yrs. Having been in the music business for twenty years Duke knows how to please the audience. Duke started doing his tribute shows after several request from the audience members to do more and more of Elvis' songs and a request for him to do an Elvis Tribute Show. Duke has been asked several times if he is lip-syching to Elvis' songs and the answer is absolutely NO. The sound and stage presence is so close to 'The King' that it has startled many.                                                                                                                                                                                                                                                                                                                                                                                                                                                |    4 |
|  http://www.gigmasters.com/elvis/DukeHicks/   | http://www.snee.com/ns/epcategory   | Elvis Impersonator, Tribute Band                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |    1 |
|  http://www.gigmasters.com/elvis/DukeHicks/   | http://www.snee.com/ns/epinfluences | Elvis Presley                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |    1 |
|  http://www.gigmasters.com/elvis/ElvisByDano/ |  dc:description                     | For a great time at your next event, how about ELVIS by Dano? His main goal is to provide a show that reflects the raw energy, passion, and humor that The King once shared with us. Dano, being a huge Elvis fan since his eleventh year, has loved singing along with The Man his entire adult life. He started to impersonate Elvis in public about 1995, and his first long solo performance, with a full set of songs, was at a church social in 2002. Dano was also a seven year member of a classic rock band and often contributed an Elvis act that audiences always truly enjoyed. Starting in February, 2004 he has performed in many solo shows for benefits, auctions, various parties , a Theme Park, as well as much time donated to entertain the elderly. He uses quality audio equipment with great sounding background tracks. Longer travel distances will be considered. Contact Dano today if you want your next party 'all shook up'!!! |    3 |
+-----------------------------------------------+-------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------+