METAXPath

1
METAXPath

• Curtis Dyreson
• E.E. and Computer Science
• Washington State University
• USA

Michael Böhlen and Christian S. Jensen Computer
Science Aalborg University Denmark
Nykredit Center for Database Research Aalborg
University, Denmark
2
Outline

• Data
• Data model
• XML
• Query language
• XPath
• Metadata
• METAXPath
• Future work

3
An XML Database Architecture
Database
Client (HTTP browser)
HTTP server
XML data and metadata
4
Database Data Model Evolution

• 60s - Hierarchical data model
• 70s - Network data model
• 80s - Relational data model
• 90s - Object-oriented data model
• 00s - Unstructured/semistructured/XML
• Innovators
• Unstructured data models (UPenn)
• UnQL/Strudel (ATT)
• OEM and Lore (Stanford)
• XML (W3C)

5
Object Exchange Model (OEM)

• Heterogeneous OODBs
• Exchange objects
• Text description

object 1
object 1
object 2
text (XML)
your database
my database
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Object Representation in XML

• Use names and values
• Ignore types
• X denotes object X

lt!ATTLIST person id ID REQUIREDgt lt!ELEMENT
person (name age)gt
// A person class class Person String
name int age // A person
object Person joe new Person(Joe Doe, 25)
ltperson id1gt ltnamegtJoe Doelt/namegt
ltagegt25lt/agegt lt/persongt
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XML (XPath) Data Model

• Each element or attribute is a node
• Edges indicate nesting
• Nodes contain information
• Tree is ordered

root
nameJoe attribute
person element
id1 attribute
ltperson id1 nameJoegt ltagegt25lt/agegt
lt/persongt
age element
/n text
/n text
XML
25 text
XPath
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Semistructured Data Model

• Each element or attribute is a node
• Edges indicate nesting
• Edges are labeled

person
ltperson id1 nameJoegt ltagegt25lt/agegt
lt/persongt
1
name
age
25
Joe
XML
Semistructured
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Data Models Compared

• Insensitive to
• text order,
• whitespace
• attributes vs. elements
• Directed graph (many roots, can contain cycles)

• Captures
• text order,
• whitespace,
• attributes and elements
• A tree (single root, no cycles)

root
nameJoe attribute
person
person element
id1 attribute
1
name
age element
/n text
/n text
age
25
Joe
25 text
Semistructured
XPath
10
Outline

• Data
• Data model
• XML
• Query language
• XPath
• Metadata
• XML - METAXPath
• Future work

11
XPath

• W3C Recommendation 1999
• Used in XQuery, XSLT, and XPointer
• Language for selecting locations in an XML
  document
• Query
• Sequence of location steps separated by /
• Location step
• axisnode_test predicate1predicateN
• Evaluated with respect to a context node
• Results in a node-set (actually a list of nodes!)
• Step continues from nodes reached in previous step

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Descendent Axis Example
root
person element
SSN99 attribute
dateOfBirth element
This comment
name element
last element
first element
month element
year element
initialS attribute
1981 text
January text
Douglas text
Susan text
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Axes that Partition a Tree

• Ancestor, descendent, following, preceding, and
  self partition a tree.

ancestor
self
preceding
following
descendent
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XPath Node Test and Predicates

• Each node in result-set must pass node test
• Is this an element node named person?
• person
• Is this an element node?
• Predicates are further tests (about other nodes)
• Does node have a ssn attribute?
• attributessn

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Example /childperson/child/childlast
root
root
person element
person element
SSN99 attribute
dateOfBirth element
This comment
name element
last element
last element
first element
last element
month element
year element
initialS attribute
1981 text
January text
Douglas text
Susan text
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XPath Examples

• The dateOfBirth children of person nodes
• /descendentperson/childdateOfBirth
• The last text node
• /descendenttext()position()last()

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Abbreviated Syntax

• Think of file path specifications in Unix
• Year child of dateOfBirth
• childdateOfBirth/childyear
• dateOfBirth/year
• name siblings
• parent/childname
• ../name
• All year nodes
• /descendent-or-self/childyear
• //year

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Outline

• Data
• Data model
• XML
• Query language
• XPath
• Metadata
• XML - METAXPath
• Future work

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Metadata

• Database metadata
• Schema, security, transaction time (versions)
• Web metadata
• Author, language, subject, privacy
• Web metadata recommendations
• RDF, RDD, P3P
• Features
• Descriptive, but also exclusionary
• Irregular
• Multiple
• Ad-hoc

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A Movie Database

• Movie data
• Bruce Willis stars in Colour of Night.
• Colour of Night premiered 1/Jul/1995.
• Publication meta-data
• language English
• URL http//www.auc.dk
• publication date 2/Apr/1997
• privacy/security over 18
• publication history v1.2, modified
  31/Jul/1998
• subject Film, Suspense,
  Thriller
• namespace http//www.auc.dk/movieD
  ataDTD.xml

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Movie Database Queries

• Metadata only
• Retrieve information published at Danish web
  sites.
• Metadata compared to data
• Find reviews published in the first week of the
  movies release.
• Metadata and data, but independent
• Get suspense films starring Bruce Willis.

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Properties of a Metadata Data Model

• Goal Same query language for data and metadata
• User learns one language
• Compiler/optimization reuse
• Challenges Data and metadata in different
  dataspaces
• Query on data should not accidently query
  metadata
• Meta-metadata
• Metadata for metadata
• Metadata has semantics
• Data with/without metadata

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METAXPath Data Model

• Data model
• Reuse XPath data model
• Meta attribute points to metadata tree
• Right angle data model
• Features
• Minimal extension of XPath
• Backwards-compatible

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Example

• Data
• lt?xml version"1.0"gt
• ltperson ssn"234"gt
• ltnamegtIchirolt/namegt
• lt/persongt
• URL metadata
• ltsource URLwww.wsu.edu/p.htmgt
• Language metadata of person element
• ltlanguagegtEnglishlt/languagegt
• Author meta-metadata - language metadata author
• ltauthor name"Suzuki"/gt

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Type root
Type element Value person Attributes (ssn, 223)
lt?xml version"1.0"gt ltperson ssn"234"gt
ltnamegtIchirolt/namegt lt/persongt
Type element Value name Attributes
Type text Value \n\t
Type text Value \n
Type text Value Ichiro
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Type root Meta
Type root
Type element Value source Attributes (URL,
www.wsu.edu/p.htm)
Type element Value person Attributes (ssn,
223)
Type element Value name Attributes
Type text Value \n\t
Type text Value \n
Type text Value Ichiro
ltsource URLwww.wsu.edu/p.htmgt
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Type root Meta
Type root
Type element Value source Attributes (URL,
www.wsu.edu/p.htm)
Type element Value person Attributes (ssn,
223) Meta
Type root
Type element Value language Attributes
Type element Value name Attributes
Type text Value \n\t
Type text Value \n
Type text Value English
Type text Value Ichiro
ltlanguagegtEnglishlt/languagegt
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Type root Meta
Type root
Type element Value source Attributes (URL,
www.wsu.edu/p.htm)
Type element Value person Attributes (ssn,
223) Meta
Type root Meta
Type root
Type element Value author Attributes (name,
Suzuki)
Type element Value language Attributes
Type element Value name Attributes
Type text Value \n\t
Type text Value \n
Type text Value English
Type text Value Ichiro
ltauthor name"Suzuki"/gt
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Sharing and Excluding Metadata

• Meta property points to metadata for a node
• Shared pointers gt shared metadata
• To share with child
• Copy pointer
• To exclude from child
• Duplicate excluded portion
• Copy remaining shared pointers

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Type root Meta
Type root
Type element Value source Attributes (URL,
www.wsu.edu/p.htm)
Type element Value person Attributes (ssn,
223) Meta
Type root Meta
Type root
Type element Value author Attributes (name,
Suzuki)
Type element Value language Attributes Meta
Type element Value name Attributes Meta
Type text Value \n\t Meta
Type text Value \n Meta
Type text Value English Meta
Type text Value Ichiro Meta
Share metadata with descendents
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Type root Meta
Type root
Type element Value source Attributes (URL,
www.wsu.edu/p.htm)
Type element Value person Attributes (ssn,
223) Meta
Type root Meta
Type root
Type element Value author Attributes (name,
Suzuki)
Type element Value language Attributes Meta
Type element Value name Attributes Meta
Type text Value \n\t Meta
Type text Value \n Meta
Type text Value English Meta
Ichiro text not authored by Suzuki
Type text Value Ichiro Meta
Type root Meta
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METAXPath Queries

• XPath plus level shift operation
• meta axis
• in abbreviated syntax
• Example - Locate data nodes with URL metadata of
  p.htm
• /descendent-or-self
• meta/childsourceattributeURL"p.htm"
  
• In abbreviated syntax
• //source_at_URL"p.htm"
• Example - Locate the URL metadata
• //source/_at_URL
• Example - Locate data that has metadata authored
  by Suzuki (meta-metadata)
• ////author_at_name"Suzuki"

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Outline

• Data
• Data model
• XML
• Query language
• XPath
• Metadata
• XML - METAXPath
• Future work

34
Metadata Semantics

• Transaction time example

2
name movie
3
name title trans. time 2/Apr/1997
- 31/Jul/1998
Color of Night
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AUCQL Collapse Example

• PropertyCollapse for name is concatenation, for
  trans. time it is temporal intersection.

1
name reviewed trans. time
1/Sep/1999 - uc
2
name movie
3
name title trans. time 1/Aug/1998
- uc
name title trans. time 2/Apr/1997
- 31/Jul/1998
Colour of Night
Color of Night
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AUCQL Additional Operations

• Coalesce - compute a distributed property value

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Thin Layer Impementation
result
METAXPath query
Metadata encoding
METAXPath Compiler
XPath query
XPath Compiler
DB
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Prototype Implementation
result
METAXPath query
METAXPath Compiler
Perl
Evaluation Tree
Query Evaluation Engine
Perl
DBM
Database API
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Summary

• METAXPath website
• http//www.eecs.wsu.edu/cdyreson/pub/MetaXPath
• AUCQL website
• VLDB 99
• Implemented research prototype
• Free, downloadable, Unix environment
• http//www.eecs.wsu.edu/cdyreson/pub/AUCQL
• Interactive query engine
• Tutorials