1 / 25

CIS 550

CIS 550. Handout 7 -- XPATH and Quilt. XPath. Primary goal = to permit to access some nodes from a given document XPath main construct : axis navigation An XPath path consists of one or more navigation steps, separated by /

fausto
Télécharger la présentation

CIS 550

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CIS 550 Handout 7 -- XPATH and Quilt

  2. XPath • Primary goal = to permit to access some nodes from a given document • XPath main construct : axis navigation • An XPath path consists of one or more navigation steps, separated by / • A navigation step is a triplet: axis + node-test + list of predicates • Examples • /descendant::node()/child::author • /descendant::node()/child::author[parent/attribute::booktitle = “XML”][2] • XPath also offers some shortcuts • no axis means child • // º /descendant-or-self::node()/ • XPath/XSL-T quickref http://www.mulberrytech.com/quickref/index.html

  3. context node aaa aaa ccc ccc aaa 2 3 1 bbb bbb 4 5 6 7 XPath- child axis navigation • author is shorthand for child::author. Examples: • aaa -- all the child nodes labeled aaa (1,3) • aaa/bbb -- all the bbb grandchildren of aaa children (4) • */bbb all the bbb grandchildren of any child (4,6) • . -- the context node • / -- the root node

  4. XPath- child axis navigation (cont) • /doc -- all the doc children of the root • ./aaa -- all the aaa children of the context node (equivalent to aaa) • text() -- all the text children of the context node • node() -- all the children of the context node (includes text and attribute nodes) • .. -- parent of the context node • .// -- the context node and all its descendants • // -- the root node and all its descendants • //para-- all the para nodes in the document • //text() -- all the text nodes in the document • @font the font attribute node of the context node

  5. Predicates • [2] -- the second child node of the context node • chapter[5] -- the fifth chapter child of the context node • [last()] -- the last child node of the context node • chapter[title=“introduction”] -- the chapter children of the context node that have one or more title children whose string-value is “introduction” (the string-value is the concatenation of all the text on descendant text nodes) • person[.//firstname = “joe”] -- the person children of the context node that have in their descendants a firstname element with string-value “Joe” • From the XPath specification: NOTE: If $x is bound to a node set then $x = “foo” does not mean the same as not ($x != “foo”) ...

  6. Unions of Path Expressions • employee consultant -- the union of the employee and consultant nodes that are children of the context node • For some reason person/(employeeconsultant) --as in regular path expressions -- is not allowed • However person/node()[boolean(employeeconsultant)] is allowed!! • From the XPATH specification: • The boolean function converts its argument to a boolean as follows: • a number is true if and only if it is neither positive or negative zero nor NaN • a node-set is true if and only if it is non-empty • a string is true if and only if its length is non-zero • an object of a type other than the four basic types is converted to a boolean in a way that is dependent on that type

  7. Axis navigation • So far, nearly all our expressions have moved us down the by moving to child nodes. Exceptions were • . -- stay where you are • / go to the root • // all descendants of the root • .// all descendants of the context node • All other expressions have been abbreviations for child::… e.g. child::para. child:is an example of an axis • XPath has several axes: ancestor, ancestor-or-self, attribute, child, descendant, descendant-or-self, following, following-sibling, namespace, parent, preceding, preceding-sibling, self • Some of these (self, parent) describe single nodes, others describe sequences of nodes.

  8. XPath Navigation Axes(merci, Arnaud) ancestor preceding-sibling following-sibling self child attribute preceding following namespace descendant

  9. XPath abbreviated syntax (nothing) child:: @ attribute:: // /descendant-or-self::node() . self::node() .// descendant-or-self::node .. parent::node() / (document root)

  10. XPath • Reasonably widely adopted -- in XML-Schema and query languages. • Neither more expressive nor less expressive than regular path expressions (can’t do (ab)* ) • Particularly messy in some areas: • defining order of results • overloading of operations, • e.g. [chapter/title = “Introduction”] • why not [ “Introduction” IN chapter/title] ?

  11. Quilt proposed by Chamberlin, Robbie and Florescu (from the authors’ slides) • Leverage the most effective features of several existing and proposed query languages • Design a small, clean, implementable language • Cover the functionality required by all the XML Query use cases in a single language • Write queries that fit on a slide • Design a quilt, not a camel

  12. Quilt/Kweelt URLs Quilt (the language) http://www.almaden.ibm.com/cs/people/chamberlin/quilt_lncs.pdf Kweelt (the implementation) http://db.cis.upenn.edu/Kweelt/ http://db.cis.upenn.edu/Kweelt/useCases (examples in these notes)

  13. bind variables where <pattern> in <XML-expression> <pattern> in <XML-expression> … <condition> construct <expression> use variables bind variables for x in <XPath-expression> y in <XPath-expression> … where <condition> return <expression> use variables Quilt = XPath + “comprehension” syntax • XML -QL • Quilt

  14. Examples of Quilt(from http://db.cis.upenn.edu/Kweelt/useCases/R/Q1.qlt ) Relational data -- two DTDs: <?xml version="1.0" ?> <!DOCTYPE items [ <!ELEMENT items (item_tuple*)> <!ELEMENT item_tuple (itemno, description, offered_by, start_date?, end_date?, reserve_price? )> <!ELEMENT itemno (#PCDATA)> <!ELEMENT description (#PCDATA)> <!ELEMENT offered_by (#PCDATA)> <!ELEMENT start_date (#PCDATA)> <!ELEMENT end_date (#PCDATA)> <!ELEMENT reserve_price (#PCDATA)> ]> <?xml version="1.0" ?> <!DOCTYPE bids [ <!ELEMENT bids (bid_tuple*)> <!ELEMENT bid_tuple (userid, itemno, bid, bid_date)> <!ELEMENT userid (#PCDATA)> <!ELEMENT itemno (#PCDATA)> <!ELEMENT bid (#PCDATA)> <!ELEMENT bid_date (#PCDATA)> ]>

  15. The data <items> <item_tuple> <itemno>1001</itemno> <description>Red Bicycle</description> <offered_by>U01</offered_by> <start_date>1999-01-05</start_date> <end_date>1999-01-20</end_date> <reserve_price>40</reserve_price> </item_tuple> <item_tuple> <itemno>1002</itemno> <description>Motorcycle</description> <offered_by>U02</offered_by> <start_date>1999-02-11</start_date> <end_date>1999-03-15</end_date> <reserve_price>500</reserve_price> </item_tuple> … </items> <bids> <bid_tuple> <userid>U02</userid> <itemno>1001</itemno> <bid>35</bid> <bid_date>99-01-07</bid_date> </bid_tuple> <bid_tuple> <userid>U04</userid> <itemno>1001</itemno> <bid>40</bid> <bid_date>99-01-08</bid_date> </bid_tuple> … </bids>

  16. Query 1 FUNCTION date() { "1999-02-01" } <result> ( FOR $i IN document("items.xml")//item_tuple WHERE $i/start_date LEQ date() AND $i/end_date GEQ date() AND contains($i/description, "Bicycle") RETURN <item_tuple> $i/itemno , $i/description </item_tuple> SORTBY (itemno) ) </result> simple function definitions XPath expressions inorange dates are formatted so that lexicographic ordering gives the right result

  17. Output from Q1 <?xml version="1.0" ?> <result> <item_tuple> <itemno> 1003 </itemno> <description> Old Bicycle </description> </item_tuple> <item_tuple> <itemno> 1007 </itemno> <description> Racing Bicycle </description> </item_tuple> </result>

  18. Query Q2 For all bicycles, list the item number, description, and highest bid (if any), ordered by item number. <result> ( FOR $i IN document("items.xml")//item_tuple LET $b := document("bids.xml")//bid_tuple[itemno = $i/itemno] WHERE contains($i/description, "Bicycle") RETURN <item_tuple> $i/itemno , $i/description , IF ($b) THEN <high_bid> NumFormat("#####.##", max(-1, $b/bid)) </high_bid> ELSE "" </item_tuple> SORTBY (itemno) ) </result> use of variable in Xpath lots of coercion

  19. Output from Q2 <result> <item_tuple> <itemno> 1001 </itemno> <description> Red Bicycle </description> <high_bid> 55 </high_bid> </item_tuple> <item_tuple> <itemno> 1003 </itemno> <description> Old Bicycle </description> <high_bid> 20 </high_bid> </item_tuple> <item_tuple> <itemno> 1007 </itemno> <description> Racing Bicycle </description> <high_bid> 225 </high_bid> </item_tuple> <item_tuple> <itemno> 1008 </itemno> <description> Broken Bicycle </description> </item_tuple> </result>

  20. Query Q3 Find cases where a user with a rating worse (alphabetically greater than "C" ) offers an item with a reserve price of more than 1000. <result> ( FOR $u IN document("users.xml")//user_tuple, $i IN document("items.xml")//item_tuple WHERE $u/rating GT 'C' AND $i/reserve_price GT 1000 AND $i/offered_by = $u/userid RETURN <warning> <user_name>$u/name/text()</user_name>, <user_rating>$u/rating/text()</user_rating>, <item_description>$i/description/text()</item_description>, $i/reserve_price </warning> ) </result> Comparing sets with singletons Same rules as in XPath? In this case the DTD gives uniqueness

  21. Quilt -- Attributes and IDs <census> <person name = "Bill" job = "Teacher"> <person name = "Joe" job = "Painter" spouse = "Martha"> <person name = "Sam" job = "Nurse"> <person name = "Fred" job = "Senator" spouse = "Jane"> </person> </person> <person name = "Karen" job = "Doctor" spouse = "Steve"> </person> </person> <person name = "Mary" job = "Pilot"> <person name = "Susan" job = "Pilot" spouse = "Dave"> </person> </person> </person> <person name = "Frank" job = "Writer"> <person name = "Martha" job = "Programmer" spouse = "Joe"> <person name = "Dave" job = "Athlete" spouse = "Susan"> </person> </person> ... </person> </census> <?xml version="1.0" ?> <!DOCTYPE census [ <!ELEMENT census (person*)> <!ELEMENT person (person*)> <!ATTLIST person name ID #REQUIRED spouse IDREF #IMPLIED job CDATA #IMPLIED > ]>

  22. Query Q1 Find Martha's spouse: FOR $m IN document("census.xml")//person[@name="Martha"] RETURN shallow($m/@spouse->{person@name}) A hack. Kweelt does not read the DTD The shallow function strips an element of its subelements. Dereferencing

  23. Query Q6 Find Bill's grandchildren. <result> ( FOR $b IN document("census.xml")//person[@name = "Bill"] , $c IN $b/person | $b/@spouse->{person@name}/person , $g IN $c/person | $c/@spouse->{person@name}/person RETURN shallow($g) ) </result>

  24. Status of XML types • DTDs -- widely used, but limited • lack of base types • untyped pointers (IDs and IDREFs) • no tuple types (hence no record subtyping or inheritance) • XML-schema -- lots of hoopla, but • not stable • too complex • Others: RDF (not really types for XML) SOX, Relax, Schematron • Opinions: • None of these is good for database design. • Something new is needed (some core of XML-schema)

  25. Status of XML Query languages • None of them are really typed (by a DTD or anything else). • Type errors show up as empty answers • XML-QL probably the most elegant, but too powerful. • XSL and descendants are working (in IE 5) • Quilt -- nice extension of XPath, but XPath is quite complex. • Nothing like an “algebra” for any of these (though some ideas are now emerging) • Nothing like database optimization yet exists. • Do we need something simpler?

More Related