Historical Perspective - DICOM Native Models from WG-23

Model Discussions in WG-23  Occurred in over a dozen meetings and t-cons  Began in early 2007, continuing through summer 2008, minor tweaks since then  Leveraged earlier work  Suggestions from Guenther Zeilinger (father of dcm4che, a widely used DICOM toolkit for Java)  David Clunie in his enhanced MR validation suite (also used in PixelMed’s DICOM toolkit)  Dongbau Guo and Oracle’s schemas for DICOM in XML  Lessons learned from other image formats (e.g. NFTI)  Participants from most major vendors, several smaller vendors, and from academia  Ideas presented and feedback solicited at multiple major conferences.

Why DSDL?  ISO/IEC Standard  Politically correct, as DICOM is an ISO Standard  ISO rules say ‘use ISO Standards when possible’  The clarity of the Relax NG Compact form  Part of target audience not well versed in XML  Separating out complex validation rules aids clarity  Rich validation capabilities of Schematron  Simple translation to other schema languages  Several tools available to translate Relax NG into XSDL, DTD, and other languages  Can use Schematron rules independent of schema

Alternatives Considered  Use XML Element names derived from DICOM Data Dictionary names  Similar to suggested schema from Emanuel  Problem with unknown DICOM Data Elements  Use XML Element names derived from numeric tag  Not as easy to work with  Strong validators could fail with unknown DICOM Data Elements – schema skew highly likely  Use VR as XML Element, with tag and name as XML Attributes  Easy to support strong type checking  Not natural to most people

Consensus Reached  Simple grammar matching DICOM encoding  Mechanical, bi-directional translation between binary DICOM and the XML Infoset model  Allows searching by either numeric tag or keyword (i.e., DICOM Attribute Name)  Stable Schema – need not change  Dictionary driven  Allows for private DICOM Data Elements  Leverages VR for potential validation  Separately defined enhanced validation using Schematron rules and assertions

Open to Suggestions, but  Any suggested changes must take into account previous decisions:  Must be bi-directional  Must take into account Private Data Elements (important for research use) without breaking  Must allow transparent pass-through (e.g. through Hosting Systems) of unknown DICOM objects  Must not break if Hosting System and Hosted Application are working off different versions of the DICOM Data Dictionary  Must not be onerous for the uninitiated to use

Possible Suggestion  Instead of a generic “Value” XML Element inside the DICOM Data Element, use a VR-specific XML Element (e.g. PNValue, LOValue, SQValue, etc.)  Still a mechanical, bidirectional translation from binary DICOM, given the UN VR  Allows for VR-specific constructs (e.g. names)  May be better for strong type checking (This was considered by WG-23, but was not incorporated. It could be presented again, if that brings a convergence.)

Should WADO use the WG-23 Model?  Having a consistent methodology for representing DICOM in XML is desirable But  Goals may be different The two WGs should converge, but only if their differing goals can be met with a single methodology.