UML class diagrams and XML schemas

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UML class diagramsand XML schemas

• Karl Lieberherr
• UBS AG
• Northeastern University

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Overview

• Translation from UML cds to XML schemas
• Other standards beyond XML Structure-shy object
  pattern
• Navigation through XML documents (and object
  structures) Structure-shy traversal pattern

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Comparison

• XML schema
• defines
• language
• structure of objects (documents)

• UML class diagram
• defines
• structure of objects
• summarizes program
• all classes
• interfaces

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Processing of Objects

• XML
• XSLT, JSP
• programs (Java etc.)
• Document Object Model
• provides a standard set of objects for
  representing XML documents
• Fine grained model one element - one class
• SAX

• UML
• programs (Java etc.)

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What brings XML?

• Agreement at syntax level
• several proposals to write schemas
• useful to have unified, simple approach to define
  mark-up languages
• Still need agreement at semantic level
• hard data integration problems not eliminated

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Commonality
Generate a visitor library from class graph for
copying, displaying, printing, checking,
comparing and tracing of objects.
XML schemas
UML class diagrams
structure of objects, Java processing
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What can OO designers learn from XML?

• It is useful to separate the structure of your
  design from the implementation
• E.g., XSLT descriptions are distinct from schemas
• It is useful to view an OO design as a grammar
  that defines application specific objects

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What are the basic elements of XML?

• Sequence
• lt!ELEMENT Compound (Op , Exp , Exp )gt
• Disjunction
• lt!ELEMENT Exp (Simple Compound )gt
• Repetition
• lt!ELEMENT Author (Person , Publication )gt

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What are the basic elements of UML class
diagrams?

• Sequence - Concrete Classes
• Compound (op Op , arg1 Exp , arg2 Exp )
• Disjunction - Abstract Classes
• Exp (Simple Compound )
• Repetition - Collection classes
• Author (Person , Publication )

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Avoid duplication!

• We should define a systematic process to generate
  XML schemas from UML class diagrams
• Has many benefits
• more flexible
• easier to maintain

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How do we have to write UML class diagrams?

• To make the translation easy (and to improve the
  UML class diagram)
• Classes are partitioned into abstract classes and
  concrete classes. Abstract classes have at least
  one subclass.
• Follow the Abstract Super Class rule (ASR). That
  means that all superclasses should be abstract.

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UML Cd to XML Schema

• The translation algorithm roughly proceeds as
  follows
• Flatten the UML class diagram, i.e., push all
  parts of abstract classes down to concrete
  classes. Replace undirected associations by two
  directed associations.Follow the ordering of
  parts and the ordering policy.
• Concrete classes are translated into a schema
  element A of the form (B1, B2, B3, ...).
• Abstract classes are translated into a schema
  element of the form A (B1 B2 B3 ...).
• An optional part B is represented as B?. A
  repeated part B is represented as B or B.