使用iSPARQL使用相似性度量来比较值

您可以使用这样的查询来查找名称类似于“Londn”的城市,并按相似性(一个度量)对它们进行排序.其余的答案解释了这是如何工作的：

select ?city ?percent where {
  ?city a dbpedia-owl:City ;
        rdfs:label ?label .
  filter langMatches( lang(?label),'en' )

  bind( replace( concat( 'x',str(?label) ),"^x[^Londn]*([L]?)[^ondn]*([o]?)[^ndn]*([n]?)[^dn]*([d]?)[^n]*([n]?).*$",'$1$2$3$4$5' ) as ?match )
  bind( xsd:float(strlen(?match))/strlen(str(?label)) as ?percent )
}
order by desc(?percent)
limit 100

SPARQL results

city                                  percent
----------------------------------------------
http://dbpedia.org/resource/London    0.833333
http://dbpedia.org/resource/Bonn      0.75
http://dbpedia.org/resource/Loudi     0.6
http://dbpedia.org/resource/Ladnu     0.6
http://dbpedia.org/resource/Lonar     0.6
http://dbpedia.org/resource/Longnan   0.571429
http://dbpedia.org/resource/Longyan   0.571429
http://dbpedia.org/resource/Luoding   0.571429
http://dbpedia.org/resource/Lodhran   0.571429
http://dbpedia.org/resource/Lom%C3%A9 0.5
http://dbpedia.org/resource/Andong    0.5

计算字符串相似性度量

Note: the code in this part of this answer works in Apache Jena. There’s actually an edge case that causes this to (correctly) fail in Virtuoso. The update at the end addresses this issue.

SPARQL中没有内置计算字符串匹配距离,但您可以使用SPARQL中的正则表达式替换机制来完成其中的一些操作.假设您想在某些字符串中匹配序列“cat”.然后你可以使用这样的查询来计算出“cat”序列中给定字符串的多少：

select ?string ?match where {
  values ?string { "cart" "concatenate" "hat" "pot" "hop" }
  bind( replace( ?string,"^[^cat]*([c]?)[^at]*([a]?)[^t]*([t]?).*$","$1$2$3" ) as ?match )
}

-------------------------
| string        | match |
=========================
| "cart"        | "cat" |
| "concatenate" | "cat" |
| "hat"         | "at"  |
| "pot"         | "t"   |
| "hop"         | ""    |
-------------------------

通过检查字符串和匹配的长度,您应该能够计算一些不同的相似性度量.作为使用您提到的“Londn”输入的更复杂的示例.百分比列是与输入匹配的字符串的百分比.

select ?input
       ?string
       (strlen(?match)/strlen(?string) as ?percent)
where {
  values ?string { "London" "Londn" "London Fog" "Lando" "Land Ho!"
                   "concatenate" "catnap" "hat" "cat" "chat" "chart" "port" "part" }

  values (?input ?pattern ?replacement) {
    ("cat"   "^[^cat]*([c]?)[^at]*([a]?)[^t]*([t]?).*$"                              "$1$2$3")
    ("Londn" "^[^Londn]*([L]?)[^ondn]*([o]?)[^ndn]*([n]?)[^dn]*([d]?)[^n]*([n]?).*$" "$1$2$3$4$5")
  }

  bind( replace( ?string,?pattern,?replacement) as ?match )
}
order by ?pattern desc(?percent)

--------------------------------------------------------
| input   | string        | percent                    |
========================================================
| "Londn" | "Londn"       | 1.0                        |
| "Londn" | "London"      | 0.833333333333333333333333 |
| "Londn" | "Lando"       | 0.6                        |
| "Londn" | "London Fog"  | 0.5                        |
| "Londn" | "Land Ho!"    | 0.375                      |
| "Londn" | "concatenate" | 0.272727272727272727272727 |
| "Londn" | "port"        | 0.25                       |
| "Londn" | "catnap"      | 0.166666666666666666666666 |
| "Londn" | "cat"         | 0.0                        |
| "Londn" | "chart"       | 0.0                        |
| "Londn" | "chat"        | 0.0                        |
| "Londn" | "hat"         | 0.0                        |
| "Londn" | "part"        | 0.0                        |
| "cat"   | "cat"         | 1.0                        |
| "cat"   | "chat"        | 0.75                       |
| "cat"   | "hat"         | 0.666666666666666666666666 |
| "cat"   | "chart"       | 0.6                        |
| "cat"   | "part"        | 0.5                        |
| "cat"   | "catnap"      | 0.5                        |
| "cat"   | "concatenate" | 0.272727272727272727272727 |
| "cat"   | "port"        | 0.25                       |
| "cat"   | "Lando"       | 0.2                        |
| "cat"   | "Land Ho!"    | 0.125                      |
| "cat"   | "Londn"       | 0.0                        |
| "cat"   | "London"      | 0.0                        |
| "cat"   | "London Fog"  | 0.0                        |
--------------------------------------------------------

更新

上面的代码在Apache Jena中有效,但在Virtuoso中失败,因为模式可以匹配空字符串.例如,如果您在DBpedia的端点(由Virtuoso提供支持)上尝试以下查询,您将收到以下错误：

select (replace( "foo",".*","x" ) as ?bar) where {}

Virtuoso 22023 Error The regex-based XPATH/XQuery/SPARQL replace()
function can not search for a pattern that can be found even in an
empty string

这令我感到惊讶,但replace的规范说它基于XPath fn:replace.fn：replace的文档说：

An error is raised [07003] if the pattern matches a zero-length
string,that is,if the expression fn:matches(“”,$pattern,$flags)
returns true. It is not an error,however,if a captured substring is
zero-length.

但是,我们可以通过在模式和字符串的开头添加一个字符来解决这个问题：

select ?input
       ?string
       (strlen(?match)/strlen(?string) as ?percent)
where {
  values ?string { "London" "Londn" "London Fog" "Lando" "Land Ho!"
                   "concatenate" "catnap" "hat" "cat" "chat" "chart" "port" "part" }

  values (?input ?pattern ?replacement) {
    ("cat"   "^x[^cat]*([c]?)[^at]*([a]?)[^t]*([t]?).*$"                              "$1$2$3")
    ("Londn" "^x[^Londn]*([L]?)[^ondn]*([o]?)[^ndn]*([n]?)[^dn]*([d]?)[^n]*([n]?).*$" "$1$2$3$4$5")
  }

  bind( replace( concat('x',?string),?replacement) as ?match )
}
order by ?pattern desc(?percent)

--------------------------------------------------------
| input   | string        | percent                    |
========================================================
| "Londn" | "Londn"       | 1.0                        |
| "Londn" | "London"      | 0.833333333333333333333333 |
| "Londn" | "Lando"       | 0.6                        |
| "Londn" | "London Fog"  | 0.5                        |
| "Londn" | "Land Ho!"    | 0.375                      |
| "Londn" | "concatenate" | 0.272727272727272727272727 |
| "Londn" | "port"        | 0.25                       |
| "Londn" | "catnap"      | 0.166666666666666666666666 |
| "Londn" | "cat"         | 0.0                        |
| "Londn" | "chart"       | 0.0                        |
| "Londn" | "chat"        | 0.0                        |
| "Londn" | "hat"         | 0.0                        |
| "Londn" | "part"        | 0.0                        |
| "cat"   | "cat"         | 1.0                        |
| "cat"   | "chat"        | 0.75                       |
| "cat"   | "hat"         | 0.666666666666666666666666 |
| "cat"   | "chart"       | 0.6                        |
| "cat"   | "part"        | 0.5                        |
| "cat"   | "catnap"      | 0.5                        |
| "cat"   | "concatenate" | 0.272727272727272727272727 |
| "cat"   | "port"        | 0.25                       |
| "cat"   | "Lando"       | 0.2                        |
| "cat"   | "Land Ho!"    | 0.125                      |
| "cat"   | "Londn"       | 0.0                        |
| "cat"   | "London"      | 0.0                        |
| "cat"   | "London Fog"  | 0.0                        |
--------------------------------------------------------