XML: How can we use it as a Logical Data Model

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XML How can we use it as a Logical Data Model?

• Murali Mani
• Sep 18, 2003

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Outline

• XML 101
• Database Design 101
• XML Schemas How to specify structures and
  constraints.
• Why use XML for database applications?
• ERex (Entity Relationship extended for XML)
  conceptual model
• Translating ERex schemas to XML schemas
• Conclusions and Future Work.

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What is XML?

• ltbookgt
• ltauthorgtJ. E. Hopcroftlt/authorgt
• ltauthorgtJ. D. Ullmanlt/authorgt
• ltpublisher nameAddison-Wesley/gt
• lt/bookgt

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XML for information exchange
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XML Publishing
XML
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XML for Data Modeling
Location ? location (_at_val, _at_time, GPS) GPS ?
gps (_at_satellite)
Location ? location (_at_val, _at_time,
Bstation) Bstation ? bstation (_at_id,
_at_sigStrength)
Location ? location (_at_val, _at_time, (GPS
Bstation))
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XML as a logical data model
Location ? location (_at_val, _at_time, (GPS
Bstation))

• Use data modeling features provided by XML
• Union types
• Recursive types
• Ordered relationships
• Easier to Query?
• Problems
• What is a good XML schema for an application?
• How do we store the data in relational databases?

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XML for data integration
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Database Design Stages
Application Requirements
Conceptual Design
Conceptual Schema
Logical Design
Logical Schema
Physical Design
Physical Schema
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Logical Data Model and Redundancy
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Specifying Structures for XML

• G (N, T, P, S)
• N Book, Author, Publisher, PCDATA
• T book, author, publisher, pcdata
• S Book
• Book ? book (Author , Publisher)
• Author ? author (PCDATA)
• Publisher ? publisher (_at_nameString)
• PCDATA ? pcdata (?)

Regular Tree Grammar Every production rule is of
the form A ? a X A ? N, a ? T, X is a regular
expression over N
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Specifying Constraints for XML
(Library, Person, lt_at_namegt) (Library, Book,
lt_at_ISBNgt) (Library, Paper, lt_at_titlegt) (Person,
Review, lt_at_articlegt)
_at_articleIDREF references (Book Paper)
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Why use XML as logical data model?
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Path Expressions vs Joins
Query Give names of students of professors of
age 40
?name ((?age40 (Professor)) ? Student)
professor _at_age40/student/_at_sname
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Union Types - attributes
Person ? person (_at_name, ((_at_city, _at_state) _at_zip))
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Union Types - Relationships
Person ? person (_at_name, _at_zip, (Book
Paper))
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Union Types - Relationships
Conference ? conference (_at_name, _at_venue,
Paper) Journal ? journal (_at_name, _at_publisher,
Paper)
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Recursive Types
Query What are subparts of bike?
WITH RECURSIVE SubPart (name) AS (SELECT name
FROM Assembly WHERE superPartbike)
UNION (SELECT R2.name FROM SubPart R1,
Assembly R2 WHERE R2.superPart R1.name) SELECT
FROM SubPart
part_at_namebike//part/_at_name
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IDREF vs Foreign Keys
_at_PRefIDREF references (Professor)
Query Give names of students of professors of
age 40
student_at_PRef?professor/_at_age40/_at_name
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IDREF as union of foreign keys
Book
Person
Paper
Review
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IDREF as union of foreign keys
_at_articleIDREF references (Book Paper)
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Conceptual Model ERex (ER extended for XML)
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From ER model
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From ER Model
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Ordered Relationships
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Categories and Set Constraints
PersonCity ? PersonZip ? PersonCity ? PersonZip
Person
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Categories
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Set constraints on Roles
personBook ? personPaper ?
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Set Constraints on Roles
confPaper ? journalPaper ? confPaper ?
journalPaper Paper
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Translating ERex schemas to XML schemas
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System Architecture
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1n relationships
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Representing 1n Relationships - subelement
University ? university (Professor) Professor ?
professor (_at_name, _at_age, Student) Student ?
student (_at_name, _at_year) (University, Professor,
lt_at_namegt) (University, Student, lt_at_namegt)
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Representing 1n Relationships - IDREF
University ? university (Professor,
Student) Professor ? professor (_at_name, _at_age,
_at_PID) Student ? student (_at_name, _at_year,
_at_PRef) (University, Professor,
lt_at_namegt) (University, Student, lt_at_namegt) _at_PRefIDR
EF references (Professor)
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Representing 1n Relationships foreign keys
University ? university (Professor,
Student) Professor ? professor (_at_name,
_at_age) Student ? student (_at_name, _at_year,
_at_advisor) (University, Professor,
lt_at_namegt) (University, Student, lt_at_namegt) (Universit
y, Student, lt_at_advisorgt) references (University,
Professor, lt_at_namegt)
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mn relationships
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Representing mn relationships
Library ? library (Person, Book) Person ?
person (_at_name, Review) Book ? book (_at_ISBN,
_at_title, _at_BID) Review ? review (_at_article,
_at_rating) (Library, Person, lt_at_namegt) (Library,
Book, lt_at_ISBNgt) (Person, Review,
lt_at_articlegt) _at_articleIDREF references (Book)
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Representing mn relationships
Book
Person
Review
Query What is the rating given by RRM for book T1
?rating ((?titleT1 (Book)) ? (?pnameRRM
(Review)))
person_at_nameRRM/review_at_article?Book/titleT1/_at_
rating
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N-ary relationships
(Root, Company, lt_at_namegt) (Root, Product,
lt_at_namegt) (Root, City, lt_at_namegt) (Company, Supply,
lt_at_ProdRef, _at_CityRefgt) _at_ProdRefIDREF
references (Product) _at_CityRefIDREF references
(City)
Root ? root (Company, Product, City) Company ?
company (_at_name, Supply) Supply ? supply
(_at_ProdRef, _at_CityRef, _at_qty) Product ? product
(_at_name, _at_ProdID) City ? city (_at_name, _at_CityID)
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Recursive Relationships
Assembly ? assembly (Part) Part ? part (_at_name,
_at_qty, Part) (Assembly, Part, lt_at_namegt)
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Ordered Relationships
Library ? library (Person) Person ? person
(_at_name, _at_zip, Book) Book ? book (_at_ISBN, _at_title)
(Library, Person, lt_at_namegt) (Library, Book,
lt_at_ISBNgt)
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Categories and set constraints
PersonCity ? PersonZip ? PersonCity ? PersonZip
Person
Person ? person (_at_name, ((_at_city, _at_state) _at_zip))
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Categories and Set Constraints
Root ? root (Person, Book, Paper) Person ?
person (_at_name, Review) Review ? review
(_at_article, _at_rating) (Root, Person,
lt_at_namegt) (Person, Review, lt_at_articlegt) _at_articleID
REF references (Book Paper)
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Set constraints on Roles
personBook ? personPaper ?
Person ? person (_at_name, (Book Paper))
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Set Constraints on Roles
confPaper ? journalPaper ? confPaper ?
journalPaper Paper
Conference ? conference (_at_name, _at_venue,
Paper) Journal ? journal (_at_name, _at_publisher,
Paper)
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Converting ERex ? XML

• Goals
• Maximize relationships represented using
  subelement.
• Others try to represent using IDREF

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Algorithm ERex ? XML

• A non-terminal symbol for each
• entity type with key
• mn relationship
• n-ary relationship
• Root non-terminal symbol
• Represent attributes
• Represent relationships and identify top nodes
• 11 and 1n relationships
• mn relationships
• n-ary relationships
• Identify key and IDREF constraints.

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personBook ? personPaper ? PersonCity ?
PersonZip ? PersonCity ? PersonZip Person
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Person ? person (Book Paper) Person ? person
(Review) Review ? review (_at_rating, _at_article)
Root ? root (Person)
N Root, Person, Book, Paper, Review Book ?
book (_at_ISBN, _at_btitle, _at_year) Paper ? paper
(_at_ptitle, _at_year, _at_journal) Person ? person
(_at_name, ((_at_city,
_at_state) _at_zip))
(Root, Person, lt_at_namegt) (Root, Book,
lt_at_ISBNgt) (Root, Paper, lt_at_ptitlegt) (Person,
Review, lt_at_articlegt) _at_articleIDREF references
(Book Paper)
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Conclusions

• Obtained good XML Schema from ERex schemas
• XML for DB applications
• Single-type tree grammars
• Constraints specified on types

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Open Problems

• Publishing relational databases/storing XML as
  relational
• Formalizing operations for XML (XPath, XQuery,
  XSLT)
• Translation of XML operations to SQL
• XML used for text/document publishing
• Keyword Search in XML documents
• Storing data consisting of structured and
  unstructured portions integrating relational and
  XML stores.

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Thank You !

• URL http//www.cs.wpi.edu/mmani
• Email mmani_at_cs.wpi.edu

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XML Schema Language Proposals

• W3C DTD local tree grammar
• W3C XML Schema single type tree grammar
• ISO/OASIS RELAX NG full-fledged regular tree
  grammar

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Properties of different Regular Tree Grammar
classes

• Expressiveness
• Regular tree grammar strictly more expressive
  than single type tree grammar
• Single type tree grammar strictly more expressive
  than local tree grammar
• Closure properties
• Regular tree grammar closed under union,
  intersection and difference
• Single type tree grammar/local tree grammar
  closed only under intersection
• Type assignment
• Type assignment can be ambiguous for regular tree
  grammar.
• Type assignment is unambiguous for local tree
  grammar/single type tree grammar.

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Ambiguous Type Assignment

• G (N, T, P, S)
• N Book, Author1, Author2, Publisher, PCDATA
• T book, author, publisher, pcdata
• S Book
• Book ? book (Author1, Author2, Publisher)
• Author1 ? author (PCDATA)
• Author2 ? author (PCDATA)
• Publisher ? publisher (_at_nameString)
• PCDATA ? pcdata (?)

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Constraint Specification for XML why?
If we represent all relationships only by
hierarchies, then the logical model will have
redundancy.

• What constraint specification?
• Key, Foreign Key
• ID/IDREF

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Specifying Constraints for XML Example
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Specifying Constraints for XML

• Keys are specified using (rel, sel, field)
• rel is relative axis
• sel is selector axis
• field is a set of path expressions
• For any element that belongs to rel, sel will
  give a set of elements. For this set of elements,
  field is the key.
• rel and sel can be types or path expressions
• Foreign keys are specified as (rel1, sel1,
  field1) references (rel2, sel2, field2)

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Constraint Specification Proposals

• W3C XML Schema
• Relative axis type
• Selector axis path expression
• Keys for XML WWW10
• Relative axis path expression
• Selector axis path expression
• UCM WWW10
• No relative axis
• Selector axis type

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Our proposal

• Relative axis type
• Selector axis type
• IDREF and IDREFS identify target types