1 / 13

XPath Help

XPath Help. Karl Lieberherr. Source of information / Plan. http://www.w3.org/TR/2005/WD-xpath20-20050915/ Complex definition We want to extract the “static” part of XPath Objective: Use / and /+/ (//) to build sequences and use operators: union, intersection and except to combine them.

ldidomenico
Download Presentation

XPath Help

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. XPath Help Karl Lieberherr

  2. Source of information / Plan • http://www.w3.org/TR/2005/WD-xpath20-20050915/ • Complex definition • We want to extract the “static” part of XPath • Objective: Use / and /+/ (//) to build sequences and use operators: union, intersection and except to combine them.

  3. Mismatches • XPath can work without schema. • But we want to visualize XPath expression in schema. • Works only for “static” XPath expressions • XPath views meaning of expression as a sequence. • Strategies views the meaning of an expression as a function that maps objects to object graph slices. Traversing slice: sequence of nodes.

  4. Mismatches • But we can also view the meaning of a strategy and a class graph as another graph: TraversalGraph

  5. XPath data model • In the data model, a value is always a sequence. • A sequence is an ordered collection of zero or more items. • An item is either an atomic value or a node. • singleton, empty sequence. Sequences are never nested.

  6. EBNF for XPath • [26]   PathExpr   ::=   ("/" RelativePathExpr?)| ("//" RelativePathExpr)| RelativePathExpr • [27]   RelativePathExpr   ::=   StepExpr (("/" | "//") StepExpr)* • [28]   StepExpr   ::=   AxisStep | FilterExpr

  7. Class dictionaries / EBNF • exercise3.txt • class dictionaries are both a simplification and extension of EBNF.

  8. EBNF for XPath • [30]   ForwardStep   ::=   (ForwardAxisNodeTest) | AbbrevForwardStep • [31]   ForwardAxis   ::=   <"child" "::">| <"descendant" "::">| <"attribute" "::">| <"self" "::">| <"descendant-or-self" "::">| <"following-sibling" "::">| <"following" "::">| <"namespace" "::">

  9. EBNF for XPath • 3.3.3 Combining Node Sequences • [14]   UnionExpr   ::=   IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )* • [15]   IntersectExceptExpr   ::=   InstanceofExpr ( ("intersect" | "except") InstanceofExpr )* • [16]   InstanceofExpr::=   PathExpr

  10. sequence operations • XPath provides the following operators for combining sequences of nodes: • The union and | operators are equivalent. They take two node sequences as operands and return a sequence containing all the nodes that occur in either of the operands. • The intersect operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in both operands. • The except operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in the first operand but not in the second operand.

  11. sequence operations $seq1 is bound to (A, B) $seq2 is bound to (A, B) $seq3 is bound to (B, C) Then: $seq1 union $seq2 evaluates to the sequence (A, B). $seq2 union $seq3 evaluates to the sequence (A, B, C). $seq1 intersect $seq2 evaluates to the sequence (A, B). $seq2 intersect $seq3 evaluates to the sequence containing B only. $seq1 except $seq2 evaluates to the empty sequence. $seq2 except $seq3 evaluates to the sequence containing A only.

  12. Declare context node type • what is meaning of / B and /+/ B?

  13. Mixing strategies and XPath?? • what would the meaning be of: • s1 : from A via B to C • s2 : A /+/ D • union (s1 s2)

More Related