recursive functions creating hierarchical reports date: 9/30/2008 dan mccreary president dan...

Recursive FunctionsCreating Hierarchical Reports

Date: 9/30/2008

Dan McCrearyPresidentDan McCreary & [email protected](952) 931-9198

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Metadata Solutions

Copyright 2008 Dan McCreary & Associates 2

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Module Outline

• Why use recursive functions?

• Sitemap example

• Taxonomy example


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Why Use Recursive Functions?

• Allows developers to create very simple data structures

• Allows hierarchical views of data

• Recursive functions are usually very short

• Allows developers to put different types of data at any level of a document


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What is Recursion?

• Functions that call themselves• Ideal for:

– Containers that contain containers– Folders that contain sub-folders– Collections that contain sub-collections– Groupings that have sub-groupings– Classification systems that have sub-

classification systems (aka Taxonomies)


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For Loop vs. Recursion

root

row

row

row

row

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root

branchbranch

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for-loop

branch

branch

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recursion


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branch

branch

branch

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How Does It Work?

• Imagine a bug crawling up a tree. When it hits a branch it spawns a new bug for each branch.

branch

branch

branch


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Site Map Example

• Sitemaps are web pages that present a summary of the structure of a web site

• Each collection can be associated with a content area

• Collections can be moved at any time so you don’t want to have to manually build a site map


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Site Maps with eXist

• Each collection will be a content area• Create a function that will list all the child-

collections of any given collection• Allow that function to call itself• Start at the site root node and get all child

collections• Use HTML nested lists to display the results


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Sample Web Site Hierarchy

/db

webroot

faqs products support about

xquery

training

xformstei

Start here

eXist rest


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Using oXygen to Create Collections

right clickover collection


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get-child-collections()

• This function takes a single input collection path returns a a set of strings, each string is a child of the current collection

xmldb:get-child-collections($collection as xs:string) as xs:string*

let $children := xmldb:get-child-collections(‘/db/webroot’)

From documentation:

Example:


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Testing get-child-collections

xquery version "1.0";

let $children := xmldb:get-child-collections('/db/webroot')

return<results> <children>{$children}</children></results>

<results> <children>about faqs training products support</children></results>

Output:

XQuery:


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For Loop

<results> <child>about</child> <child>faqs</child> <child>training</child> <child>products</child> <child>support</child></results>


<results>{ for $child in xmldb:get-child-collections('/db/webroot') return <child>{$child}</child>}</results>

XQuery:

Output:


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Declare Sitemap Function

declare function local:sitemap($collection as xs:string) as node()* {

for $child in xmldb:get-child-collections($collection) return <ul> <li>{$child}</li> {local:sitemap(concat($collection, '/', $child))} </ul>};


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Test Function


declare function local:sitemap($collection as xs:string) as node()* { for $child in xmldb:get-child-collections($collection) return <ul> <li>{$child}</li> {local:sitemap(concat($collection, '/', $child))} </ul>}; <site>{local:sitemap('/db/webroot')}</site>


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Results

<site> <ul> <li>about</li> </ul> <ul> <li>faqs</li> </ul> <ul> <li>training</li> <ul> <li>xforms</li> </ul> <ul> <li>rest</li> </ul>

<ul> <li>xquery</li> </ul> </ul> <ul> <li>products</li> </ul> <ul> <li>support</li> </ul></site>


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HTML Output

<html> <head> <title>Sitemap</title> </head> <body> {local:sitemap('/db/webroot')} </body></html>


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HTML UL Output


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Adding HTML Links

declare function local:sitemap($collection as xs:string) as node()* {

for $child in xmldb:get-child-collections($collection) return <ul> <li><a href="{concat('/exist/rest', $collection, '/', $child)}">{$child}</a></li> {local:sitemap(concat($collection, '/', $child))} </ul>};


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Output

http://localhost:8080/exist/rest/db/webroot/about


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Adding Level

• Add another parameter called “level” to the sitemap function that is of type integer. Start the root with level 0 and increment the level each time you call yourself

<body> {local:sitemap('/db/webroot')}</body>


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Adding Titles

• Most Sitemaps create a “user friendly” title that might include mixed case and spaces.

• Create a lookup table that stores a label or title for each collection. The title might include spaces and other special characters that are not used in collection names.

<code-table> <item> <path>/db/webroot/training</path> <title>Training</title> </item> <item> <path>/db/webroot/faqs</path> <title>Frequently Asked Questions</title> </item></code-table>

$title := $code-table/item[$path=path]/title


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Output


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Taxonomy

• A hieratical classification system based on subject areas

Thing

PersonLocationEvent Publication

Book BlogArticle


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Taxonomy Lab

• Create a simple hierarchical taxonomy management system similar to the Dewey decimal system for libraries.

• Put individual items in XML files.• Call the root item “Thing”. Create narrower terms for “Person”,

“Event”, “Organization”, “Place” and “Publication”• Each “item” has one-and-only-one broader term.• Create functions for get-narrower-items(), and get-hierarchy()

<item> <id>3</id> <label>Person</label> <definition>An individual Human Being</definition> <broader-id>1</broader-id></item>


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Thank You!

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

Dan McCreary, PresidentDan McCreary & Associates

Metadata Strategy [email protected]

(952) 931-9198

recursive functions creating hierarchical reports date: 9/30/2008 dan mccreary president dan...

Documents

collection return

existeach collection

web siteeach collection

html output sitemap

collectionsthis function

single input collection

site root node

subclassification systems