Extensive use of fx:anySlot - query not terminating

[enridaga]

We stumbled on one query using fx:anySlot extensively, which does not terminate.

The query:

PREFIX fx: <http://sparql.xyz/facade-x/ns/>
PREFIX xyz: <http://sparql.xyz/facade-x/data/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX tsub: <http://sparql.xyz/example/tate/topic/>
PREFIX schema: <http://schema.org/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

CONSTRUCT {
	?artwork schema:about ?topic .
	?topic schema:name ?name .
} WHERE {
  SERVICE <x-sparql-anything:location=./a00002-1036.xml> {
	[] a xyz:children; fx:anySlot [a xyz:item; fx:anySlot [ a xyz:id; fx:anySlot ?topicId]; fx:anySlot [ a xyz:name; fx:anySlot ?name ]] .
#     The alternative without fx:anySlot works
#	[] a xyz:children; ?li1 [a xyz:item; ?li2 [ a xyz:id; ?li3 ?topicId]; ?li4 [ a xyz:name; ?li5 ?name ]] .
#     This pattern uses fx:anySlot once but does not seem to create problems (leaving this one only works)
	[] a xyz:url; fx:anySlot ?artworkUrl .
	BIND(IRI(?artworkUrl) as ?artwork) .
	BIND(IRI(CONCAT(STR(tsub:),STR(?topicId))) AS ?topic) .
	FILTER (?topicId != xyz:id) .
	FILTER (?name != xyz:name) .
	FILTER (?artworkUrl != xyz:url) .
  }
}

The data:

<artwork>
	<acno>A00002</acno>
	<acquisitionYear>1922</acquisitionYear>
	<creator>
		<name>Robert Blake</name>
		<birthYear>1762</birthYear>
		<gender>Male</gender>
		<id>38</id>
	</creator>
	<creditLine>Presented by Mrs John Richmond 1992</creditLine>
	<height>213</height>
	<id>1036</id>
	<medium>Graphite on paper</medium>
	<topics>
		<children>
			<children>
				<children>
					<item>
						<id>273</id>
						<name>comforting</name>
					</item>
					<item>
						<id>544</id>
						<name>embracing</name>
					</item>
					<item>
						<id>2653</id>
						<name>recoiling</name>
					</item>
				</children>
				<item>
					<id>177</id>
					<name>actions: expressive</name>
				</item>
			</children>
			<children>
				<children>
					<item>
						<id>451</id>
						<name>figure</name>
					</item>
				</children>
				<item>
					<id>95</id>
					<name>adults</name>
				</item>
			</children>
			<children>
				<children>
					<item>
						<id>799</id>
						<name>group</name>
					</item>
				</children>
				<item>
					<id>97</id>
					<name>groups</name>
				</item>
			</children>
			<item>
				<id>91</id>
				<name>people</name>
			</item>
		</children>
		<children>
			<children>
				<children>
					<item>
						<id>2815</id>
						<name>fear</name>
					</item>
				</children>
				<item>
					<id>31</id>
					<name>emotions and human qualities</name>
				</item>
			</children>
			<item>
				<id>29</id>
				<name>emotions, concepts and ideas</name>
			</item>
		</children>
		<item>
			<id>1</id>
			<name>topicRoot</name>
		</item>
	</topics>
	<title>Two Drawings of Frightened Figures, Probably for 'The Approach of Doom'</title>
	<units>mm</units>
	<url>https://www.tate.org.uk/art/artworks/blake-two-drawings-of-frightened-figures-probably-for-the-approach-of-doom-a00002</url>
	<width>311</width>
</artwork>

The query plan:

  (filter (exprlist (!= ?topicId <http://sparql.xyz/facade-x/data/id>) (!= ?name <http://sparql.xyz/facade-x/data/name>) (!= ?artworkUrl <http://sparql.xyz/facade-x/data/url>))
    (extend ((?topic (iri (concat "http://sparql.xyz/example/tate/topic/" (str ?topicId)))))
      (extend ((?artwork (iri ?artworkUrl)))
        (bgp
          (triple ??0 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://sparql.xyz/facade-x/data/children>)
          (triple ??0 <http://sparql.xyz/facade-x/ns/anySlot> ??1)
          (triple ??1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://sparql.xyz/facade-x/data/item>)
          (triple ??1 <http://sparql.xyz/facade-x/ns/anySlot> ??2)
          (triple ??2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://sparql.xyz/facade-x/data/id>)
          (triple ??2 <http://sparql.xyz/facade-x/ns/anySlot> ?topicId)
          (triple ??1 <http://sparql.xyz/facade-x/ns/anySlot> ??3)
          (triple ??3 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://sparql.xyz/facade-x/data/name>)
          (triple ??3 <http://sparql.xyz/facade-x/ns/anySlot> ?name)
          (triple ??4 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://sparql.xyz/facade-x/data/url>)
          (triple ??4 <http://sparql.xyz/facade-x/ns/anySlot> ?artworkUrl)
        )))))

[luigi-asprino]

The engine instantiated the triple pattern for evaluating the fx:anySlot property wrongly (subject and object were considered wildcards even if they were blank nodes).