Overview of XPath Author: Dan McCreary Date: October, 2008 Version: 0.2 with TEI Examples M D.

Overview of XPath

Author: Dan McCreary

Date: October, 2008

Version: 0.2 with TEI ExamplesM

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Copyright 2008 Dan McCreary & Associates 2

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Objectives

• Provide a short overview of XPath

• Describe why knowledge of XPath is important for:– Business analysts

– Project managers

– Report developers

– Programmers

• Demonstrate XPath using TEI document


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Definition XPath

• XPath: "A language for addressing parts of an XML document"

• Similar to a DOS or UNIX "file system path" but with powerful expressions

• XPath is to XML what the SQL "select" statement is to SQL

• XPath is not a full programming language or a query language.


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XPath Related Standards

• XSLT – XPath is used to tell XSLT how to match tags• XLink – similar to HTML links <a> but more powerful• XPointer - a standard manner for identifying document

fragments• XQuery – a newer, more comprehensive standard that

includes XPath 2.0 and allows more complex searches and data types include relational database searches. Includes clauses for "for, let, where, order-by, return"


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Versions

• Version 1.0– W3C Recommendation November, 16 1999– http://www.w3.org/TR/xpath

• Version 2.0– W3C Working Draft October, 29 2004– http://www.w3.org/TR/xpath20/


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Other Familiar Path Names

• DOS:– C:\Program Files\Altova\XMLSPY2004\Examples\Tutorial

• Web– http://www.google.com/search?hl=en&lr=lang_en&&q=XPath

• Unix– /usr/local/lib/mylib/myprogram.jar

• Similarities– Absolute path starts with "/"

– Relative paths express do not start with "/"


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XPath Has Relative Expressions

self

child

parent

ancestor

sibling

descendant

sibling

preceding following

ancestorancestor

following-sibling

child child

descendantdescendant

preceding-sibling


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Location Steps

• An XPath expression contains one or more "location steps", separated by slashes. Each location step has the following unabbreviated form:– axis-name :: node-test [predicate]*

• The abbreviated form is more commonly used, so that is what this example uses. It refers to the child axis:– node-test [predicate]*


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XPath Also Provides

• XPath has functions for manipulation of:– Nodes and sets of nodes (elements-NameTest,

KindTest)– Strings (substring, contains etc.)– Numbers (position etc.)– Booleans (and/or/not etc.)


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Disclaimer

• Example was chosen for teaching purposes only

• Not necessarily indicative of a full actual TEI structure


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oXygen XPath Builder

Perspective > Show View > XPath Builder


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Sample XML Document<TEI xmlns="http://www.tei-c.org/ns/1.0"

xmlns:frus="http://history.state.gov/2008/frus">

<teiHeader>

<fileDesc>

<titleStmt>

<title type="complete">Foreign Relations of the United States, 1969-1976, Volume

E-13: Documents on China, 1969-1972</title>

<title type="series">Foreign Relations of the United States</title>

<title type="subseries">1969-1976</title>

<title type="volumenumber">Volume E-13</title>

<title type="volume">Documents on China, 1969-1972</title>

<editor role="primary">Steven E. Phillips</editor>

<editor role="general">Edward C. Keefer</editor>

</titleStmt>


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TEI Tree

text

TEI namespace

teiHeader

front body

div type="compilation"

head pb

div type=“document"

pbdiv type=“document"


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90/10 rule for XPath

• 90% of the time your XPath expressions will be very simple.

• They will be just getting subsets of all the data in the document

• They will use the default “child” selector


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Sample XPath Child Expressions

• Find the root element of any document–/

• Find the root element–/TEI

• Find the TEI Header–/TEI/teiHeader

• Find the text body–/TEI/text/body

• Find the text body headers–/TEI/text/body/div/head

• Find the text body sub headers–/TEI/text/body/div/head/div/head


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Selecting Attributes

• To select an attribute you must add the @ symbol to the expression

• Example: select only the divs that have an attribute type="document"– //div[@type="document"]


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Getting Data with //

• Get all the person names in the document– //persName

• Get all the dates or notes in the document– //date

• Get all the notes of type summary

//note[@type='summary']


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Sample Counts

• Count of the number of paragraphs in the document– count(//p)

• Count of the number of divs– count(//div)

• Count of the number of person names– count(//persName)


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What’s the Context?

• XPath evaluates expressions relative to a context.– Usually specified by one of the technologies

that extend XPath, such as XSLT and XPointer.– Includes context node, context size, context

position, etc.

• In XSLT, the context node is the current node being evaluated.


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Sample XPath Syntax

• Test for equality– node=‘value’

• [ ] – predicate, e.g. First in sequence: [1] • Last: last()• * - wildcards• @ - attributes• // - all children of the context node• . – context node itself• .. – parent of the context node


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XPath String Operations

concat

starts-with

ends-with

contains

substring

string-length

substring-before

substring-after

normalize-space

normalize-unicode

upper-case

lower-case

translate

string-pad

matches

replace

tokenize

escape-uri


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Boolean Operators

• boolean(1 and 1) returns true• (1 and 0) returns false• (1 or 0) returns true• (1 and 1 and (1 or 0)) returns true


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Contains()

• Returns true if the first string passed contains the second string passed

• Example:– //p[contains(.,'President')]


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Benefits of XPath

• Business analysts– Precise specification of constraints, support for graphical representation of

rules, easy to change.

• Project managers– Shorten development cycle, easier to change business logic.

• Report developers– Pattern matching language for routing of documents based on rules,

platform and language neutral.

• Programmers– Functions available for manipulating nodes, sets of nodes, strings, numbers,

or boolean. Based on regular expressions and mathematical model. Good for mapping and transforming documents from one type to another.


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To Find Out More

• XPath 2.0 Programmer's Reference– by Michael Kay

• Definitive XSLT and XPath– by G. Ken Holman

• XSLT and XPath– John Robert Gardner and Zarella L. Rendon


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Thank You!

Please contact me for more information:• XML Development• Metadata Management Services• Web Services• Service Oriented Architectures• Business Intelligence and Data Warehouse• Metadata Registries• Semantic Web

Dan McCreary, PresidentDan McCreary & Associates

Metadata Strategy [email protected]

(952) 931-9198

Overview of XPath Author: Dan McCreary Date: October, 2008 Version: 0.2 with TEI Examples M D.

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