Augmenting Traditional Conceptual Models to Accommodate XML Structures Stephen W. Liddle Information...

Augmenting Traditional Conceptual Models to Accommodate XML Structures

Stephen W. LiddleInformation Systems Department

Reema Al-Kamha & David W. EmbleyComputer Science Department

Brigham Young University, Provo, Utah

2 of 255 November 2007 ER 2007, Auckland, New Zealand

Outline

Background XML modeling criteria Missing modeling constructs C-XML Augmenting ER and UML Conclusion


The Need for Greater Abstraction

The history of modeling and programming languages is the history of our attempts to scale the mountain of abstraction

XML needs better abstractions


XML Schema/Model Mismatch

XML features not explicitly supported in traditional conceptual models: Ordered lists of concepts Choice of concept from among several Nested information hierarchies Mixed content Use of content from another model


Our Contributions

Proposed conceptual representation for XML structures

Representation of these concepts in ER and UML


XML Modeling Criteria

Graphical notation Formal foundation Structure independence Reflection of the mental model N-ary relationship sets Logical level mapping Cardinality for all participants Irregular & heterogeneous structure Document-centric data

Views Constraints Ordering


Missing Modeling Constructs (1)

Sequence structure Parent concept Ordered child concepts Constrained recurrence of children Constrained recurrence of sequence itself

<xs:sequence minOccurs="1" maxOccurs="2"> <xs:element name="FirstName" type="xs:string"/> <xs:element name="MiddleName" type="xs:string“ minOccurs="0" maxOccurs="2"/> <xs:element name="LastName" type="xs:string"/></xs:sequence>



Choice structure Parent concept Choose one child concept from several

alternatives Constrained recurrence of chosen child Constrained recurrence of choice itself

<xs:choice maxOccurs="2"> <xs:element name="PhoneNumber" type="xs:string" minOccurs="1" maxOccurs="2" /> <xs:element name="Email" type="xs:string"/> <xs:element name="Fax" type="xs:string"/></xs:choice>



Mixed attribute Allows character and element data to be

intertwined <xs:complexType mixed="true">

Any and anyAttribute structures Insert structures from other namespaces Constrained recurrence <xs:any namespace="##other" minOccurs="0"/> <xs:anyAttribute namespace="##any"/>



Nesting of hierarchical structures Key organizational characteristic of XML Arbitrarily complex nesting possible


C-XML Augmentations

C-XML foundation proposed at ER 2004 Augmented hypergraph of relationship sets

and object sets Sequence Choice Any/anyAttribute Mixed content


C-XML Example


C-XML Modeling Sufficiency

Graphical notation

Formal foundation

Structure independence

Reflection of the mental model

N-ary relationship sets

Logical level mapping

Cardinality for all participants

Irregular & heterogeneous structure

Document-centric data

Views

Constraints

Ordering


C-XML Advantages w.r.t. XML

Structure independence Associate multiple sequences/choices with a single

concept Intermix ordinary relationship sets with

sequences/choices Generalized sequence, choice, mixed content

Reflection of mental model Represent hierarchical and non-hierarchical structure No attribute vs. element decision Both ordered and unordered related concepts Choice distinguished from generalization/specialization Full range of cardinality constraints


Other Conceptual Models for XML

We are not the only ones working on this See surveys by Sengupta & Wilde (2003) and

Necasky (2006) XML Schema itself responds in part to the

need for better conceptual models of XML But there is more to be done


Methodology

The market wants standards Consider popular conceptual models

ER UML (class diagrams)

Find related work that maps those models to XML XER (XML for ER) by Sengupta et al. Conrad et al. work on UML

Compare their work with C-XML to identify problems Extend their work to XML Schema

XER ER-XML Conrad UML-XML


XER (Best Attempt)


XER Issues

Lacks some cardinality constraints Missing any and anyAttribute constructs No representation for composite keys Can only apply key designation to attributes Combines notions of choice and

generalization/specialization in one construct This is a conceptual mismatch for various reasons

Need to allow for anonymous entities We made many assumptions to present a cleaned up

version of XER as ER-XML


ER-XML (XER++)


Conrad UML/XML (Best Attempt)


Conrad UML/XML Issues

Key construct: Extended UML aggregation to map choice and

sequence structures Lack of anyAttribute construct Lack of mixed content construct Lacks key constraints

Unless you count OCL Sequence/choice representation can only be

applied to classes, not attributes


UML-XML (Conrad++)


C-XML Advantages Formal foundation

XER not formally defined UML formal description not fully developed

Reflection of mental model No attribute/element distinction required

Views Hypergraphs are amenable to view translations C-XML has high-level views (object sets and relationship

sets) as a first-class construct Logical level mapping

We have mapped both XML Schema C-XML and C-XML XML Schema

Cardinality for all participants C-XML handles cardinality constraints for more participants

even than than XML Schema supports


Conclusion

Problem: some XML Schema concepts are missing in traditional conceptual models

Solution: enrich conceptual models with ability to Order a list of concepts Choose alternatives from among several Specify mixed content Use content data from another data model


Conclusion

C-XML answers the need Our solution can be adapted to ER and UML

languages Though these adaptations aren’t quite as good

at satisfying modeling requirements as C-XML

Augmenting Traditional Conceptual Models to Accommodate XML Structures Stephen W. Liddle Information...

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