Introduction to XSLT
As a tool for humanities computing
4 XPath
ALLC/ACH 2002, Tübingen
21-22 July 2002
C. M. Sperberg-McQueen
Wendell Piez
- I.1. Overview
- I.2. XPath
- I.3. XPath: an addressing language
- I.4. XPath data model
- I.5. Data model example
- I.6. Data model example
- I.7. XPath expressions
- I.8. XPath steps
- I.9. XPath selection axes
- I.10. XPath long syntax: simple
- I.11. Long syntax: more complex
- I.12. Long syntax: predicates
- I.13. XPath short syntax
- I.14. XPath as query language
- I.15. Examples: searching
I. Sunday afternoon 2: XPath
Overview |    1 of 15 |
- Sunday a.m.: introductions
- Sunday a.m.: basics (simple transformations, if, choose, selection by attribute values)
- Sunday p.m.: modes (e.g. tables of contents)
- Sunday p.m.: XPath
- Monday a.m.: functions, numbering
- Monday a.m.: near-identity transformations
- Monday p.m.: named templates, recursion
- Monday p.m.: sorting and grouping
XPath | 2 of 15 |
- What is XPath?
- XPath data model
- Expressions as location ladders
- Axes
- Long syntax, short syntax
XPath: an addressing language | 3 of 15 |
Many applications need to ‘address’ parts of
XML documents:
- formatting (e.g. XSLT)
- hyperlinking
- document construction
- query / search and retrieval
- schema / language specification
- ...
XSLT select and
match values are XPath expressions.
XPath data model | 4 of 15 |
A document is an ordered tree with
- a root node
- element nodes
- text nodes
- attribute nodes
- namespace nodes
- processing instructions
- comment nodes
Data model example | 5 of 15 |
Data model example | 6 of 15 |
XPath expressions | 7 of 15 |
An expression is a sequence of steps:
/step/step/step/step ...
Each step
- starts from some current node(s),
- moves to some result node(s).
XPath steps | 8 of 15 |
A step is
where
E.g. descendant::figure[@rend="svg"]
axis::node test
[predicate]
[predicate] ...
axis says what direction to move
node test says which nodes go into result
predicate adds further constraints
XPath selection axes | 9 of 15 |
- child (→ e, t, c, p)
- parent (→ e)
- attribute (→ a)
- following, following-sibling (→ e, t, c, p)
- preceding, preceding-sibling (→ e, t, c, p)
- self
- namespace (→ n)
- ancestor, ancestor-or-self (→ e)
- descendant, descendant-or-self (→ e, t, c, p)
XPath long syntax: simple | 10 of 15 |
- child::para
- child::* (all element children)
- child::text() (all text node children)
- child::node() (all children)
- attribute::name
- attribute::*
- descendant::para
- ancestor::div
- ancestor-or-self::div
- descendant-or-self::para
Long syntax: more complex | 11 of 15 |
- self::para (context node if para, otherwise nothing)
- child::chapter/descendant::para
- child::*/child::para (all para grandchildren)
- /
- /descendant::para (all para elements in the document)
- /descendant::olist/child::item
Long syntax: predicates | 12 of 15 |
- child::para[position()=1]
- child::para[position()=last()]
- child::para[position()=last()-1]
- child::para[position()>1]
- following-sibling::chapter[position()=1]
- preceding-sibling::chapter[position()=1]
- /descendant::figure[position()=42]
- /child::doc/child::chapter[position()=5]/child::section[position()=2]
- child::para[attribute::type="warning"]
- child::para[attribute::type='warning'][position()=5]
- child::para[position()=5][attribute::type="warning"]
- child::chapter[child::title='Introduction']
- child::chapter[child::title]
- child::*[self::chapter or self::appendix]
- child::*[self::chapter or self::appendix][position()=last()]
XPath short syntax | 13 of 15 |
- para
- * (all element children)
- text() (all text node children)
- node() (all children)
- @name
- @*
- //para
- chapter/descendant::para
- */para (all para grandchildren)
- para[1]
- /doc/chapter[5]/section[2]
- para[@type="warning"]
- para[@type='warning'][5]
- para[5][@type="warning"]
- chapter[title='Introduction']
- chapter[title]
- *[self::chapter or self::appendix]
XPath as query language | 14 of 15 |
XPath and XSLT already widely used for queries.
- select elements, attributes, strings, numbers
- select by position in tree, generic identifier, attribute name, value, content
- co-occurrence constraints
- no data types
- no type safety
Examples: searching | 15 of 15 |
- An XSLT-driven search engine.
- Exercises from Greenstein, A historian's guide to computing. (See exercises page.)