Modelling

1
Modelling

• Hachim Haddouti
• Al Akhawayn University
• SSE
• H.Haddouti_at_alakhawayn.ma
• http//mail.alakhawayn.ma/H.Haddouti

2
TOC

• Intro
• DTD, XML Schmea
• Derivation of Schemainformationen from XML
  Documents
• Metrics
• Recommendations

3
Schema for XML Documents

• DTDs
• ( SGML, simple, compact, easily readable, no XML
  Syntax)
• XML Schema
• (more presentation possibilties, Data types,
  exact cardinalities, ...)

4
Document Type Definitions

• See slides of first chapter

5
XML Schema /2

• In May 2001, XML Schema officially
• More presentation possibilities,
• Simpler schema language
• More built-in datatypes
• Ability to define own datatypes
• Ability to restrict datatype values,
• Syntax closer to that of XML
• more complexity than DTD

6
Built-in Types
www.w3.org/TR/2001/REC-xmlschema-2-20010502
7
Extensibility of XML schemas

• Namespace a collection of type definitions and
  element declarations.
• Can be shared between different schema to aid in
  the reuse of types and constructs.
• Expand more on you own (Namespace Qualification,
  target namespaces, importing/inlcuding/redefining
  namespaces

8
Definition von Integrity Check

• Integrity Conditions to be met in XML Documents
• uniqueness
• key
• Referential integrity (keyref).  
• Definition of Elements and Attributes using Xpath
  expression.

9
Referential integrity

• Recall ID, IDREF
• can these serve as primary/foreign keys?

10
Referential integrity

• Uniqueness
• XML Schema enables us to indicate that any
  attribute or element value must be unique within
  a certain scope
• Fields defined as unique cannot contain null
  values
• Still not a candidate for primary/foreign key

11
Relationship constraints, cont.

• KEY, KEYREF
• like unique, key must be unique within a certain
  scope
• key can be based on multiple fields
• key can be referenced
• analogous to primary/foreign key
• Compare ID in DTD to key in XML Schema? Global
  Uniqueness?

12
Example

• ltxskey name"Hotel_key"gt
• ltxsselector xpath"/Hotelinformationen/Hotel"
  /gt
• ltxsfield xpath"_at_HotelID/"/
• lt/xskeygt
•  
• ltxskeyref name"Hotel_directory_keyref"
  refer"Hotel_keygt
• ltxsselector xpath"/ Hotel_directory
  /Location/Hotels"/gt
• ltxsfield xpath"_at_HotelID"/gt
• lt/xskeyrefgt
• selector indicate a node set, that has to be
  unique.
• With field you specify exactly, which element
  value or Attribut should be unique.

13
Key, Keyref Defining a combined key
ltxselement name"vehicle"gt ltxscomplexTypegtlt!--
begin anonymous type--gt . . . ltxsattribute
name"plateNumber" type"xsinteger"/gt
ltxsattribute name"state" type"twoLetterCode"/gt
lt/xscomplexTypegt lt/xselementgt
14
Key, Keyref Defining a combined key
ltxselement name"person"gtlt!--new global
element--gt ltxscomplexTypegt ltxssequencegt .
. . ltxselement name"car"gtlt!-- begin local
element--gt ltxscomplexTypegt
ltxsattribute name"regState" type"twoLetterCode"
/gt ltxsattribute name"regPlate"
type"xsinteger"/gt lt/xscomplexTypegt
lt/xselementgt lt/xssequencegt
lt/xscomplexTypegt lt/xselementgt
15
Key, Keyref Defining a combined key
ltxskey name"regKey"gt lt!-- vehicles are keyed
by a pair of state and plate --gt ltxsselector
xpath".//vehicle"/gt lt!--node group -gt scope --gt
ltxsfield xpath"_at_state"/gt ltxsfield
xpath"_at_plateNumber"/gt lt!-- combination must
be unique--gt lt/xskeygt ltxskeyref
name"carRef" refer"regKey"gt ltxsselector
xpath".//car"/gt ltxsfield xpath"_at_regState"/gtlt!
-- order and type important --gt ltxsfield
xpath"_at_regPlate"/gt lt/xskeyrefgt
16
Tradeoffs

• DTDs
• Large Amount of Tool Support
• Established
• Non-XML Syntax
• No typing of values
• Difficult to specify unordered sets of
  subelements
• For high speed validation, DTDs may outperform
  Schema
• XML Schema
• More control over scope of elements and where
  they can be used
• XML syntax
• Datatypes
• Namespaces
• Able to specify sets more precisely
• Less Tool Support
• More complicated language

17
XML Schema vs. DTD

• XML Schema contains all modelling abilities of
  DTD, except Entities.
• Conversion DTD in XML Schema lossless, Entities
  will be expanded.
• Conversion XML Schema in DTDs with loss

18
Usage of XML Schema

• Data centric Applications
• Import in and Export from DBs
• Use data types and integrity checks
• XML Databases SQL/XML

19
Tools

• Editors
• XMLSpy (www.xmlspy.com)
• XML Authority (www.extensibility.com/xml_resources
  /modeling.htm)
• XML Writer
• XML-Prozessors
• XML Schema Quality Checker of IBM alphaworks
  (www.alphaworks.ibm.com/tech/xmlsqc)
• XML Schema Validator of Oracle (technet.oracle.com
  /tech/xml/)