cotton 2

Querying XML Documents: 

Querying XML Documents Paul Cotton ZIG Washington, Dec 7, 2000

Organization of Presentation: 

Organization of Presentation XML query history and QL’98 XML Query WG history, goals and status XML Query Requirements XML Query Data Model XML Query Algebra Questions

XML query history : 

XML query history Early 1998: “roll your own query language” XSL Working Group XSLT needed syntax to select nodes XML Linking Working Group XPointer needed syntax to select a location February 1999 joint meeting Rapprochement on 90% of syntax XPath W3C recommendation with XSLT

XML query history - 2: 

XML query history - 2 Early queries facilities for SGML Academic research into semi-structured data and its operations XQL: See http://metalab.unc.edu/xql XML-QL, August, 1998 http://www.w3.org/TR/NOTE-xml-ql/

Query Languages Workshop ’98: 

Query Languages Workshop ’98 W3C sponsored workshop Boston (USA), December 2-3, 1998 98 participants: W3C members, database vendors, invited experts, etc. 66 position papers See: http://www.w3.org/TandS/QL/QL98

W3C XML Query WG - History : 

W3C XML Query WG - History July 1999 -Working Group proposed as part of XML Activity Phase 3 rechartering September 1999 - WG chartered More than 30 W3C member companies Eight F2F meetings and 40+ telcons so far Close working relationship with other W3C Working Groups (Schema, XSL, I18N)

W3C XML Query WG - Goals: 

W3C XML Query WG - Goals “The goal of the XML Query WG is to produce a data model for XML documents, a set of query operators on that data model, and a query language based on these query operators.”

W3C XML Query WG - Status : 

W3C XML Query WG - Status Jan 2000 – Requirements Working Draft May 2000 – XML Query Data Model WD May 2000 – Feedback on Schema Last Call August 2000 – Revised Requirements Working Draft with Use Cases Dec 2000 – XML Query Algebra WD Future public WDs every three months Proposed recommendation(s)

XML Query Requirements: 

XML Query Requirements Usage Scenarios General Requirements XML Query Data Model Requirements XML Query Functionality Use cases for XML queries http://www.w3.org/TR/xmlquery-req

General Requirements: 

General Requirements Non-procedural query language XML syntax for query language but also a readable syntax Protocol independent Standard error conditions Future support for updates

XML Query Data Model: 

XML Query Data Model Built on XML Infoset and PSV Namespace aware Support for XML Schema data types Support for inter- and intra- document references

XML Query Functionality: 

XML Query Functionality Operators on all data types Text operators across element boundaries Support for hierarchy and sequence Ability to combine data from different locs Aggregation and sorting Combination of operators including queries as operands

XML Query Functionality - 2: 

XML Query Functionality - 2 Support for NULL values Structural preservations Identity preservation Operations on names Operations on “schemas” Extensibility Closure

XML Query Data Model WD: 

XML Query Data Model WD Defines information available to a query processor Infoset plus the following: Support for XML Schema data types (PSV) Support for document collections Support for references Node-labelled tree constructor model with node identity Mapping from Infoset to Query Data Model defined in Annex A http://www.w3.org/TR/query-datamodel/

XML Query Algebra WD: 

XML Query Algebra WD Defines operations on Query Data Model Simple principles, easy to use Firm mathematical foundation Many issues still open References Unordered data Algebra subset of syntax? http://www.w3.org/TR/query-datamodel/

Questions: 

Questions Today Later: pcotton@microsoft.com Feedback email list: www-xml-query-comments@w3.org Public email list: www-ql@w3.org