Pervasive e-commerce with XML Babak Esfandiari Carleton University Ottawa, Canada

XML introduction eXtensible Markup Language “a markup language for documents containing structured information” (Walsh) this structure is defined mainly with a set of tags subset of SGML HTML can be seen as an instance of XML (it is not really though, but that is not important…)

XML example Paris

DTD Document Type Definition Describes the XML tagset <!DOCTYPE Museum [ ]> Not mandatory (!)

XML - what for? content is independent from rendering meta-data makes search easier standard tags enable data interchange across tools format for data and object persistence, human readable and editable no need for a custom parser anymore

TourTags “The purpose of TourTags.org is to foster dialogue within the community in order to arrive at open standards for conducting electronic commerce by settling on common tag sets and methods in which they are to be used.” supports IFITT’s RMSIG

XML and TourTags derive a tagset from RMSIG specs discuss/modify the tagset use the tagset for B2B (ebXML) allow device-neutral access to business info we have a process…

The Acronym Hell Diagram our process is a series of transformations UML XMI XML/ DTD ebXML Web form XML Voice XML WML HTML meta-data registrationdocumentdisplay

Meta-data Why not directly model tags? Tags are not for modeling! Lack of a graphical notation Semantically poor: Hard to represent relationships XML can be seen as one possible mapping of a model The RMSIG has chosen UML… UML XMI XML/ DTD

Meta-data UML: Unified Modeling Language Object-oriented Graphical Covers: Requirements Static representation Activities and processes UML XMI XML/ DTD

Meta-data A UML class diagram: UML XMI XML/ DTD

Meta-data But we need the tags! Is it possible to transform UML into XML? We can use XMI XMI is the direct textual representation of UML using the XML format Most UML tools support XMI UML XMI XML/ DTD

Meta-data A sample XMI document: Museum name UML XMI XML/ DTD

Meta-data We still need to transform XMI into our XML tagset Since a DTD describes the structure of an XML document, it is the ideal target! What is the easiest way to do the concrete transformation? UML XMI XML/ DTD

Transformations Different methods: Parsing: use existing XML parsing libraries based on standard APIs (SAX, DOM) with a programming language Transformations: specify the transformations in a (yet another) XML document called an XSLT stylesheet Use an XSLT processor (Saxon, XT, …)

XSLT example (excerpt) blah

XSLT example The XSLT in the previous slide, applied on the Museum XMI, should generate something like: blah Museum blah name Nothing exciting but you get the idea!

Meta-data Some of the issues in the transformation from XMI to DTD: Ambiguity in choice of attributes and elements -> open for discussion! Inheritance: compound the inherited attributes Composition: recursively add sub- elements, or use separate documents DTDs support for primitive types is limited… XML schema an alternative UML XMI XML/ DTD

Registration The resulting DTDs can now be used for B2B e-commerce We now have a domain “ontology” to base transactions on! We can use this ontology to: Publish/advertize a business Search for a business We need a registry to enable that ebXML Web form

Registration ebXML is one of the leading consortiums for e-business It describes a standard for B2B registries Third parties (TourTags?) have the opportunity to create and host such registries To access such registries and allow publishing and search, Web forms are an intuitive front-end interface Guess what… ebXML Web form

Registration We can use the DTDs and XSLT to generate such web forms! The web forms for publishing and search are very similar Each leaf element or attribute becomes a field to fill in Better support (than DTDs) for data types would allow for a better customization of the data fields ebXML Web form Museum name:

Registration Different deployment scenarios are possible for registries: Traditional Client/server Peer to peer Decentralized Less resource intensive ebXML Web form

Document rendering The result of a registry search is an XML document that follows the structure specified by our DTD Such a document does not contain any instructions for rendering (i.e. display) This is a good thing! XML Voice XML WML HTML

Search and rendering rendering adapted to device: XML -> HTML for web browser XML -> WML for cell phones XML -> VoiceXML for regular phones Yes, we can use XSLT again! No duplication of data! No need to maintain redundant documents! XML Voice XML WML HTML

Conclusion A completely XML-based process that takes us from the inception of a domain ontology to the delivery of business info The process relies on a series of transformations

References xml.org rmsig.org tourtags.org ebxml.org It had to be on the web!