针对wikidata优化聚合查询

Question

我正在运行一个针对wiki数据的聚合查询。该查询试图计算电影的平均持续时间，按其类型和出版年份分组。

查询中的多个分组/子查询旨在保留从电影到分组标准(年份和类型)的n-1关系，以及电影与其持续时间之间的1-1关系。这样做的原因是有大致正确的聚合( OLAP和数据仓库实践者熟悉的n-1关系)。

查询中嵌入了更多解释。因此，我不能放下在子查询和if语句或组连接中完成的分组。此查询在Wikidata SPARQL端点上超时。

问题

我需要一些提高绩效的建议.有优化暗示吗？如果这是不可能的，任何人都知道认证的方式(让他们知道我没有在玩)来查询维基数据，这样就可以增加超时时间，或者使用的方式增加超时(通常是)

    # Average duration of films, grouped by their genre and the year of publication       
SELECT  
        ?genre1                    # film genre
        ?year1                     # film year of publication
        (AVG(?duration1) AS ?avg)   # film average duration

WHERE
        {      
            # Calculating the average duration for each single film.
            # As there are films with multiple duration, these durations are 
            # averagred by grouping aggregating durations by film.
            # Hence, a single duration for each film is projected out from the subquery.
            {
              select ?film (avg(?duration) as ?duration1)  
              where{
                ?film   <http://www.wikidata.org/prop/direct/P2047>   ?duration .    
              }group by ?film
            }

            # Here the grouping criteria (genre and year) are calculated.
            # The criteria is grouped by film, so that in case multiple 
            # genre/multiple year exist for a single film, all of them are
            # group concated into a single value.
            # Also in case of a lack of a value of year or genre for some
            # specific film, a dummy value "OtherYear"/"OtherGenre" is generated.
            {
              select ?film (
                                IF
                                (
                                    group_concat(distinct ?year ; separator="-- ") != "", 
                                    # In case multiple year exist for a single film, all of them are group concated into a single value.
                                    group_concat(distinct ?year ; separator="-- "), 
                                   # In case of a lack of a value of year for some specific film, a dummy value "OtherYear" is generated.
                                    "OtherYear"                                        
                                )
                                as ?year1
                              )
                                (
                                IF
                                (
                                    group_concat(distinct ?genre ; separator="-- ") != "",
                                    # In case multiple genre exist for a single film, all of them are group concated into a single value.
                                    group_concat(distinct ?genre ; separator="-- "), 
                                    # In case of a lack of a value of genre for some specific film, a dummy value "OtherGenre" is generated.
                                    "OtherGenre"  
                                )
                                as ?genre1
                              ) 

              where 
              {
                ?film  <http://www.wikidata.org/prop/direct/P31>  <http://www.wikidata.org/entity/Q11424> .
                 optional {
                   ?film   <http://www.wikidata.org/prop/direct/P577>  ?date .
                   BIND(year(?date) AS ?year)
                 }
                 optional {
                   ?film <http://www.wikidata.org/prop/direct/P136>  ?genre .
                 }
              } group by ?film              
          }

        } GROUP BY ?year1 ?genre1

Answer 1

在将两个IF表达式替换为一个简单的sample (从组中选择一个任意值)之后，该查询似乎可以工作：

    (sample(?year) as ?year1)
    (sample(?genre) as ?genre1) 

因此，group_concat的费用问题似乎是主要问题。我不觉得这很直观，也没有任何解释。

也许带有sample的版本足够好，或者至少它可以为您提供一个进一步改进的基准点。