ZIG Meeting

  Notes provided primarily by Les Wibberley.

Querying XML Documents

• Paul Cotton
• formerly worked for Fulcrum, and worked on Z39.50 awhile ago
• also worked on SQL standards
• will make the slides available
• QML Query history and QL '98
• early 1998 - roll your own query language was the feeling
• XSL working Group
• XSLT needed syntax to select nodes
• XML  Linking working group
• XPointer needed a syntax to select a location
• Feb 1999 joint meeting
• 90% overlap of needs and syntax
• resulted in XPath
• W3c recommendation XSLT
• common subroutine used by both standards efforts
• this was the start
• early query facilities for sgml
• academic research into semi-structured data and its operations
• XQL - see http://metalab.unc.edu/xql
• X ML-QL August 1998
• http://www.w3.org/TR/NOTE=xml.ql
• Query Languages workshop 98
• w3c sponsored workshop
• boston dec 2-3 1998
• 98 participants
• see position papers published
• see http://www.w3.org/TandS/QL/QL98
• W3C XML Query WG
• July 1999 WG proposed as part of xml re-chartering  activity
• Sept. 1999 WG chartered
• 8 face to face meetings, and 45 teleconferences
• close working relationship with other w3c working groups (schema, XSL, 118N)
• close relationship between xml schema's and xml query WG
• 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
• status of w3c xml query WG
• jan 2000 requirements working draft
• may 2000 xml query data model
• may 2000 feedback on schema last call - this WG made majority of comments
• august 2000 revised requirements working draft with use cases (sample documents with queries written in english, and answers in xml)
• dec 2000 xml query algebra working draft
• future public working drafts every three months
• proposed recommendations
• XML query requirements
• usage scenarios
• 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
• query data model
• built on xml Infoset and PSV- Post ... Value
• Namespace aware - using xml Namespace
• support for xml schema data types
• support for inter- and intra- document references
• be able to follow links
• query functionality
• operators on all data types
• text operators across element boundaries
• support for hierarchy and sequence
• ability to combine data from different locations
• aggregation and sorting
• combination of operators including queries as operands
• support for null values
• structural preservations
• identity preservation
• operations on names
• operations on schema's
• extensibility
• closure
• xml query data model draft
• defines info available to a query processor
• infoset plus following
• support for xml schema data types
• 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/
• QML query algebra working draft
• 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-....
• Data model and types
• intro to the query algebra
• data model is essentially an alternative syntax of xml
• example of xml schema and corresponding algebra
• schema deals with inbound schema; query worries about both inbound and outbound schema
• query language will be very strongly typed (indicate integers, etc.)
• each answer specifies the data type
• a lot of this query languages heavily leverages the XPath conventions and semantics
• language includes Joins and Selections, etc.
• regrouping can eliminate duplicates
• small set of operators and types used to build the query language
• how many people participate
• chair of the w3c working group
• participants in good standing must attend most meetings, or are removed
• 20-25 on teleconferences
• 30-35 face to face
• w3c members have a prime and secondary rep; only one present
• generally about 10 people do most of the work on a w3c working group
• signing up for w3c working group commits 20% of your time
• cotton doesn't represent microsoft on the WG
• microsoft has two other strong reps involved
• people can join the WG at any time - this is a challenge
• this presentation was given at xml 2000 yesterday

• wrapup
• email pcotton@microsoft.com
• public email list: www-ql@w3.org

 

• Mark Needleman
•     xml QL
• query language only
• formal data model and algebra
• may have multiple syntaxes, but one language
• protocol independent
• may embed some of the functionality of Z39.50 directly into the language
• Z39.50
• more than just a query language
• supports multiple types of query
• provides session management, result set management, etc.
• xml QL vs z39.50
• ql-sml bases
• Z39.50 ASN ber based
• QL protocol dependent
• Z39.50 very much protocol dependent
• all functionality expressed in the query lang
• z39.50 provides supporting info retrieval beyond the query
• QL - a de facto standard?
• Z39.50 an official standard
• possible futures
• add as one more query type in Z39.50?
• abandon Z39.50 and just use functionality and model of QL
• combination
• Z39.50 in future
• retain concepts and mode of info retrieval provided by current protocol expressed using xml QL but run over a more modern transport like http and or xml protocol
• Questions
• how does xml-ql relate to Z39.50
• not yet clear how people implement the query language
• first version will specify syntax which can be used in many environments
• current model in the marketplace today is where xml is exported from repositories; now looking for query language to go with it
• right now XPath is being used as a query language (including microsoft); generates query; view database as xml document
• will move the QL up front to replace XPath
• easiest route for Z is to provide access to XML resources by adding the new Query language as a new Query Type, until more is known about the impact of this query language on the industry
• xml query language does not require concrete xml on the other end; could be a virtual xml view of existing data repositories
• may map xml query language onto underlying data at the server end
• xml query group includes representatives from all the database producers, etc., who want to ensure this will work for them
• what is the relationship between xml query and xml protocol?
• e.g., xml query over SOAP will be similar to Z39.50, but built on w3c standards family
• Z implementors mapped Z39.50 onto legacy systems
• we have found the need to negotiate features to map to real implementations
• foresee mechanism to negotiate subset of query language/functionality in the xml - QL
• A: this is the conformance aspect, which is addressed later, not earlier, so query group has not worked on it yet
• venture capital companies are asking the standards group about this, to invest in companies planning to implement xml-ql
• there will be a huge momentum behind this work
• could define a Z39.50 search service that could run over SOAP, and negotiate it (similar to business negotiation)
• the query language is only one step over the larger picture
• how does Z39.50 model some of the emerging needs
• issue of what is built into the model vs what is extensible
• convinced that xml QL will need an extensibility mechanism that allows definition of extended functions
• you can't define all of the functionality of the standard - this will probably be used to handle full text searching as extension to standard
• the server could recognize or not recognize extended functions; based on Namespace, for example