Query. Ewan Klein. MASWS 12 February Multi-agent Semantic Web Systems: Query. Ewan Klein. Outline. Introduction RSS.

Transcription

1 ing with ing with MASWS 12 February 2008

2 1 ing with ing with 2 3 ing with 4 ing with 5

3 ing RDF Data ing is crucial to being able to use RDF data. ing with ing with

4 ing RDF Data ing with ing is crucial to being able to use RDF data. Allows data across different data repositories to be combined. ing with

5 ing RDF Data ing with ing with ing is crucial to being able to use RDF data. Allows data across different data repositories to be combined. Allows selected data to be re-used and re-presented.

6 ing RDF Data ing with ing with ing is crucial to being able to use RDF data. Allows data across different data repositories to be combined. Allows selected data to be re-used and re-presented. Compare and.

7 ing with ing with feed (or channel) is a kind of document. Typically consists of a summary of content from a web site Rich Site Summary 0.90, 1.0 RDF Site Summary 2.0: Really Simple Syndication Also Atom See (file format)

8 Node Tree for the del.icio.us Feed rss:title text: del.icio.us/recent?min=2 rss:channel rss:link text: %3Fmin%3D2... ing with ing with rdf:rdf rss:item rss:title rss:link... rdf:li text: SimpleFlickr Plugin... text: attribute: rdf:resource dc:topics rdf:bag rdf:li attribute: rdf:resource rss:item rdf:li attribute: rdf:resource...

9 Pick a path A path expression: /rdf:rdf/rss:item/dc:topics/rdf:bag/rdf:li ing with ing with

10 Pick a path A path expression: /rdf:rdf/rss:item/dc:topics/rdf:bag/rdf:li Reading from right to left: ing with ing with

11 Pick a path ing with A path expression: /rdf:rdf/rss:item/dc:topics/rdf:bag/rdf:li Reading from right to left: Select every node with tag rdf:li ing with

12 Pick a path ing with ing with A path expression: /rdf:rdf/rss:item/dc:topics/rdf:bag/rdf:li Reading from right to left: Select every node with tag rdf:li that s the direct child of an rdf:bag element

13 Pick a path ing with ing with A path expression: /rdf:rdf/rss:item/dc:topics/rdf:bag/rdf:li Reading from right to left: Select every node with tag rdf:li that s the direct child of an rdf:bag element that s the direct child of a dc:topics element

14 Pick a path ing with ing with A path expression: /rdf:rdf/rss:item/dc:topics/rdf:bag/rdf:li Reading from right to left: Select every node with tag rdf:li that s the direct child of an rdf:bag element that s the direct child of a dc:topics element that s the direct child of an rss:item element

15 Pick a path ing with ing with A path expression: /rdf:rdf/rss:item/dc:topics/rdf:bag/rdf:li Reading from right to left: Select every node with tag rdf:li that s the direct child of an rdf:bag element that s the direct child of a dc:topics element that s the direct child of an rss:item element that s the direct child of the rdf:rdf element

16 Pick a path ing with ing with A path expression: /rdf:rdf/rss:item/dc:topics/rdf:bag/rdf:li Reading from right to left: Select every node with tag rdf:li that s the direct child of an rdf:bag element that s the direct child of a dc:topics element that s the direct child of an rss:item element that s the direct child of the rdf:rdf element at the root of the document ( / ).

17 The path through the node tree rss:title text: del.icio.us/recent?min=2 rss:channel rss:link text: %3Fmin%3D2... ing with ing with rdf:rdf rss:item rss:title rss:link... rdf:li text: SimpleFlickr Plugin... text: attribute: rdf:resource dc:topics rdf:bag rdf:li attribute: rdf:resource rss:item rdf:li attribute: rdf:resource...

18 Parsing and ing with Python s ElementTree ing with ing with Parse the Tree from urllib import urlopen import xml.etree.elementtree as ET #tree = ET.parse(urlopen(" tree = ET.parse(open( dlcs-rss-recent.xml )) # Find the root element of the tree root = tree.getroot()

19 Parsing and ing with Python s ElementTree ing with ing with the Tree # path is dc:topics/rdf:bag/rdf:li path = %s/%s/%s/%s % (( item ), DCTAX( topics ), for li in root.findall(path): print li.get(rdf( resource )) findall() returns a list of Elements. get(<attrib>) returns an Element s value for the attribute <attrib>.

20 Get the whole subtree rss:title text: del.icio.us/recent?min=2 rss:channel rss:link text: %3Fmin%3D2... ing with ing with rdf:rdf rss:item rss:title rss:link... rdf:li text: SimpleFlickr Plugin... text: attribute: rdf:resource dc:topics rdf:bag rdf:li attribute: rdf:resource rss:item rdf:li attribute: rdf:resource...

21 Parsing and ing with Python s ElementTree ing with ing with Results from

22 Remarks on Basic idea: search along paths in an tree. ing with ing with

23 Remarks on Basic idea: search along paths in an tree. XPath provides an exact syntax for this. ing with ing with

24 Remarks on ing with ing with Basic idea: search along paths in an tree. XPath provides an exact syntax for this. Most modern programming languages provide rich support for parsing and querying.

25 Remarks on ing with ing with Basic idea: search along paths in an tree. XPath provides an exact syntax for this. Most modern programming languages provide rich support for parsing and querying. ElementTree is a Pythonic variant; not meant to be the only or even the best way to do query.

26 ing with ing with A pattern is matched against the RDF data. Each way a pattern can be matched yields a solution. The sequence of solutions can be filtered. Four kinds of result forms, depending on query: SELECT, CONSTRUCT, ASK, (DESCRIBE) (Some material based on

27 Patterns ing with ing with Based on triples. Combination of URIs/QNames, literals and variables. Variable names:?var, $var cannot start with an integer, or contain :, - or..

28 SELECT Example ing with ing with foaf: < _:a foaf:name "Ewan". _:a foaf:mbox _:b foaf:name "Harry". PREFIX foaf: < SELECT?name WHERE {?x foaf:name?name. } Results (as Python List) ["Ewan", "Harry"]

29 Matching ing with ing with matches the graph: find a set of variable value bindings, such that result of replacing variables by values is a triple in the graph. Solution 1: variable?x has value blank node :a and variable?name has value "Ewan" Triple ( :a foaf:name "Ewan") is in the graph. Solution 2: variable?x has value blank node :b and variable?name has value "Harry" Triple ( :b foaf:name "Harry") is in the graph.

30 Multiple Patterns, 1 ing with ing with foaf: < _:a foaf:name "Ewan". _:a foaf:mbox <mailto:ewan@inf.com>. _:b foaf:name "Harry". PREFIX foaf: < SELECT?name WHERE {?x foaf:name?name.?x foaf:mbox <mailto:ewan@inf.com>. } Results ["Ewan"]

31 More on patterns ing with ing with Dots. separate patterns in the query. Can use N3 abbreviatory syntax PREFIX foaf: < SELECT?name WHERE {?x foaf:name?name ; foaf:mbox <mailto:ewan@inf.com>. }

32 Multiple Patterns, 2 ing with ing with foaf: < _:a foaf:name "Ewan". _:a foaf:knows _:b. _:b foaf:name "Harry". PREFIX foaf: < SELECT?name1?name2 WHERE {?x foaf:name?name1 ; foaf:knows?y.?y foaf:name?name2. } Results [("Ewan", "Harry")]

33 Example ing with ing with PREFIX dlcstag: < PREFIX dc8: < SELECT?post?tag WHERE {?post dc8:topics?bag.?bag?li?tag. } Results [(< dlcstag:e-learning), (< dlcstag:reference), (< dlcstag:web2.0), (< dlcstag:wiki), (< dlcstag:mindmapping), (< dlcstag:cartes_heuristique),...]

34 Forms ing with ing with SELECT: Like SQL; returns a tuple of values. CONSTRUCT: Builds a new graph by inserting values into a triple pattern. ASK: Asks whether a query has a solution in a graph.

35 -based query depends on paths through the node tree. ing with ing with

36 -based query depends on paths through the node tree. matches triple patterns in the RDF graph. ing with ing with

37 -based query depends on paths through the node tree. matches triple patterns in the RDF graph. -based query depends on knowing the syntactic structure of the serialization. ing with ing with

38 ing with -based query depends on paths through the node tree. matches triple patterns in the RDF graph. -based query depends on knowing the syntactic structure of the serialization. There are different but equivalent serializations of RDF in ; ing with

39 ing with ing with -based query depends on paths through the node tree. matches triple patterns in the RDF graph. -based query depends on knowing the syntactic structure of the serialization. There are different but equivalent serializations of RDF in ; these would require different queries.

40 ing with ing with -based query depends on paths through the node tree. matches triple patterns in the RDF graph. -based query depends on knowing the syntactic structure of the serialization. There are different but equivalent serializations of RDF in ; these would require different queries. query depends on knowing the graph structure of the RDF store.

41 ing with ing with -based query depends on paths through the node tree. matches triple patterns in the RDF graph. -based query depends on knowing the syntactic structure of the serialization. There are different but equivalent serializations of RDF in ; these would require different queries. query depends on knowing the graph structure of the RDF store. There are different but equivalent serializations of RDF (in, N3,... );

42 ing with ing with -based query depends on paths through the node tree. matches triple patterns in the RDF graph. -based query depends on knowing the syntactic structure of the serialization. There are different but equivalent serializations of RDF in ; these would require different queries. query depends on knowing the graph structure of the RDF store. There are different but equivalent serializations of RDF (in, N3,... ); these can all be matched using the same query.

43 ing with ing with -based query depends on paths through the node tree. matches triple patterns in the RDF graph. -based query depends on knowing the syntactic structure of the serialization. There are different but equivalent serializations of RDF in ; these would require different queries. query depends on knowing the graph structure of the RDF store. There are different but equivalent serializations of RDF (in, N3,... ); these can all be matched using the same query. We ll have some exercises in the next assignment :-)