XML Standards & Tools for Detector Description

May 8, 2000 ATLAS Collaboration Page 1

XML Standards & Toolsfor Detector Description

Frank Olken

Lawrence Berkeley National Laboratory

presented to ATLAS Collaboration

May 8, 2000


Outline to Talk

• XML Standards Family– XML, XML Namespaces, XML Schema,

XSLT, SVG, …

• Express to XML mappings – (ISO TC 184 STEP)

• XML Tools – Parsers, editors, DB load/unload, …


Purposes of XML

• Intended for document structure mark up

• Intended for data exchange

• Mediocre data modeling facilities

• Not intended for data storage representation

• Portability paramount

• Tends to be verbose (due to mnemonic tags)


Significance of XML

• Modest technical improvements over prior art

• Major advantage: industry consensus– IBM, Oracle, Microsoft, Sun, Informix, ...

• Implication: lots of tools, portability


XML 1.0

• Simplified version of SGML (like HTML)

• Markup metalanguage

• Application specific tag sets

• Uses DTDs (Document Type Defn) to specify document structure

• No built-in semantics

• Standard approved several years ago


XML Namespaces

• Provides segmented address space

• Avoids collisions of tag names

• Full namespaces are URI references (URLs)

• Abbreviated namespace references are “<abbrev:tagname>”

• Hot debate of usage as values (references)

• Approved as W3C recommendation (tags)– usage as data values still being debated


XML Schema Language

• Will replace DTDs (Doc. Type Def’n.)

• Uses XML syntax– hence can be created and processed with XML

tools

• Has basic datatypes:– integer, float, double, datetime, string, URIref

• Currently in last call, candidate rec. in June


XML Schema Language (cont.)

• Deficiencies:– Lacks collection types (set, bag, sequence)– Lacks vector, array types– Lacks complex number types– Lacks measurement units– Lacks multiple inheritance– Lacks versioning– Limited extensibility mechanisms


XML Schema Language (cont.)

• New standards should use XML Schema instead of DTDs !!!

• Advantages:– more, better tools– schema-driven validating parsers can check

basic data types– new tools are emerging now, throughout

summer and fall


XSLT

• Extensible Style Language (Translation)

• Language to describe XML to XML mappings (or to HTML, or to text)

• Uses XML syntax

• Useful for styling XML (e.g., to HTML)

• Useful for message format translation, etc.

• Standard is in last call.


DSSSL: Document Style Semantics and Specification

Language

• Developed for formatting SGML

• Can be used with XML

• Based on Scheme (a LISP dialect)

• See Jade (James Clark’s DSSSL Engine)

• See Open Jade project


Scalable Vector Graphics

• Standard for encoding 2D vector graphics

• Browser plug-ins available now to render – e.g., Adobe, ...

• Allows browser to pan/zoom

• Standard is in last call

• Ugly syntax


XMI = XML Metadata Interchange Format

• Originally, encoding of UML models in XML

• For exchange of UML models and data stored in UML specified

• Developed by Object Management Group

• Now in version 1.1 (uses namespaces)

• V 1.2 (XML Schema based) in development


STEP to XML Mappings

• Standard for the Exchange of Product Data

• Includes several geometry representations

• EXPRESS = modeling language – (extended entity relationship model)

• STEP Part 28 – maps STEP datasets/schemas into XML

• Currently being drafted by ISO TC 184


STEP to XML Mappings (cont.)• XML encoding of EXPRESS schemas

• Multiple encodings of STEP data to XML

• Late binding STEP data to XML– generic XML DTD, not schema specific– limited utility

• Early Binding STEP to XML– attribute-based encoding (poor)– element-based encoding (preferred)


STEP to XML Mappings (cont.)

• EXPRESS to UML mapping– UML = Unified Modeling Language– UML popular modeling methdology

• UML to XML mapping– Called XMI by Object Mgt. Group– Hence: EXPRESS -> UML -> XMI– Advantage: exploits UML to XMI tools– Disadvantage: complex, verbose XML


XML Tools

• XML Schema editors

• Structured XML document editors

• XSLT Stylesheet editors/debuggers

• XML Parsers

• XSLT engines

• Storage/query engines


XML DTD / Schema Editors

• Structured editors for XML DTDs, Schemas

• Used to create document structure specs

• XML Authority schema editor– from Extensibility– handles multiple DTD/schema languages

• IBM’s alphaWorks Schema Editor

• XML Spy, et al. …


XML Structured Document Editors

• DTD / schema based editors

• Used for word processing, data entry, ...

• Context constrained tag generation

• Automatic generation of closing tags

• Immediate datatype checking (if schemas)

• Xmetal, Adept, XML Pro, …


XML Stylesheet Editors

• Structure-based editor for XSLT stylesheets

• Multi-window user interface – (XML source, XSLT stylesheet, output)

• XSLT Debugging tools– single step execution– identification of which rule fired


XML Parsers

• Parsers process XML input files for applications programs

• Non-validating parsers only check for well formedness – (matching opening and closing tags)

• Validating parsers check syntax – (conformance to DTD/schema)

• Use validating parsers - catch errors early


XML Parser API’s

• SAX 1.0 and 2.0– event-based, – suitable for stream processing - e.g. querying

• DOM API– based on Document Object Model (parse tree)– requires entire DOM in memory– suitable for sorting portions of document,

restructuring documents, etc.


XML Parsers (cont.)

• Many good free parsers available

• Available in C, C++, Java, Python, Perl

• XP (J. Clark), RXP (R. Tobin), ...

• IBM, Sun, Microsoft, Oracle, ...

• IBM + Sun donated to Apache

• Schema support this spring or summer


XSLT Processors

• XSLT = XSL Transformation Language

• XML to XML or HTML (or text)

• Suitable for most message reformatting

• Also for XML to XSL formatting objects

• XT (James Clark)

• Saxon (Windows xx only)

• Lotus XSL (Java Bean from IBM )


Browser support of XML

• IE 5.0 (now) has (nonstd.) XML support– directly renders XML

• Netscape 6.0 (April) may render XML(?)

• Opera 4.0 (alpha now) supports XML

• Alternatives:– server side translation to HTML– plug-ins (e.g. transcode to HTML)


XML Storage

• Alternative approaches:– relational DBMS– hybrid object/relational DBMS– object oriented DBMS

• How finely to decompose document?

• Vendors:– Excelon, IBM, Oracle, Software AG, Informix,

Infoshark


XML Query Engines

• W3C XML Query Language WG at work

• XML QL will permit direct query of XML– synthesis of XML encoded query results

• Proposals:– IBM, Microsoft, ATT, Software AG, …

• Products:– Nimble.com


Conclusions

• XML Schema Lang. v.1.0 is nearly done

• Use XML Schema Language not DTDs

• Use schema-driven validating parsers

• Use SVG for 2D Vector Graphics

• Many schema driven document editors available shortly (XML Spy, Xmetal, …)


Acknowledgements

• This work has been supported entirely by the U.S. Environmental Protection Agency.

• Program managers: Bruce Bargmeyer and Mike Cullen.


XML Information Sources

• w3c.org (World Wide Consortium - XML stds) • xml.com (O’Reilly web site)• Robin Cover’s XML Web Page at OASIS• oasis-open.org (XML DTD/Schema Registry)• ebxml.org (e-commerce architecture)• biztalk.org (Microsoft)• xml.apache.org (XML in Apache webserver)


XML Information Sources

• wfmc.org (Workflow Mgt. Coalition - now AIIM)• XML Journal, XML Magazine, ...• gca.org

– XTECH Conference (February in San Jose)

– XML Europe Conference (June in Paris)

– Extreme Markup Conference (August in Montreal)

– XML 2000 (Washington, DC in December)

• Inside DTDs (book on scientific MLs)

Documents

XML Standards & Tools for Detector Description