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Native XML Support in DB2 Universal Database Matthias Nicola, Bert van der Linden IBM Silicon Valley Lab mnicola@us.ibm.com. Sept 1, 2005. Agenda. Why “native XML” and what does it mean? Native XML in the forthcoming version of DB2 Native XML Storage XML Schema Support XML Indexes

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Sept 1, 2005


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    1. Native XML Support in DB2 Universal Database Matthias Nicola, Bert van der LindenIBM Silicon Valley Labmnicola@us.ibm.com Sept 1, 2005

    2. Agenda • Why “native XML” and what does it mean? • Native XML in the forthcoming version of DB2 • Native XML Storage • XML Schema Support • XML Indexes • XQuery, and the Integration with SQL • Summary

    3. XML Databases • XML-enabled Databases • The core data model is not XML (but e.g. relational) • Mapping between XML data model and DB’s data model is required, or XML is stored as text • E.g.: DB2 XML Extender (V7, V8) • Native XML Databases • Use the hierarchical XML data model to store and process XML internally • No mapping, no storage as text • Storage format = processing format • E.g.: Forthcoming version of DB2

    4. Problems of XML-enabled Databases • CLOB storage: • Query evaluation & sub-document level access requires costly XML Parsing – too slow ! • Shredding: • Mapping from XML to relational often too complex • Often requires dozens or hundreds of tables • Complex multi-way joins to reconstruct documents • XML schema changes break the mapping • no schema flexibility ! • For example: Change element from single- to multi-occurrence requires normalization of relational schema & data

    5. Relational XML Integration of XML & Relational Capabilities in DB2 • Native XML data type • (not Varchar, not CLOB, not object-relational) • XML Capabilities in all DB2 components • Applications combine XML & relational data SERVER CLIENT SQL/X DB2 Storage: Relational Interface DB2 Client / Customer Client Application Hybrid DB2 Engine XQuery XML Interface

    6. Native XML Storage • DB2 stores XML in parsed hierarchical format (similar to the DOM representation of the XML infoset) create table dept (deptID char(8),…, deptdoc xml); • Relational columnsare stored in relationalformat (tables) • XML is stored nativelyas type-annotated trees(representing theXQuery Data Model). DB2 Storage

    7. dept employee employee id=901 name phone office id=902 name phone office John Doe 408-555-1212 344 Peter Pan 408-555-9918 216 0 String table 0 dept 4 employee 4 4 1 name 5 id 5=901 1 2 3 4=902 1 2 3 2 phone 3 office John Doe 408-555-1212 344 Peter Pan 408-555-9918 216 Efficient Document Tree Storage <dept> <employee id=901> <name>John Doe</name> <phone>408 555 1212</phone> <office>344</office> </employee> <employee id=902> <name>Peter Pan</name> <phone>408 555 9918</phone> <office>216</office> </employee> </dept> • Reduces storage • Fast comparisons & navigation SYSIBM.SYSXMLSTRINGS • 1 String table per database • Database wide dictionary for all tags in all XML columns

    8. Information for Every Node • Tag name, encoded as unique StringID • A nodeID • Node kind (e.g. element, attribute, etc.) • Namespace / Namespace prefix • Type annotation • Pointer to parent • Array of child pointers • Hints to the kind & name of child nodes (for early-out navigation) • For text/attribute nodes: the data itself

    9. XML Node Storage Layout • Node hierarchy of an XML document stored on DB2 pages • Documents that don’t fit on 1 page: split into regions/pages • Docs < 1 page: 1 region, multiple docs/regions per page Example: Document split into 3 regions, stored on 3 pages Split can be at anylevel of the document

    10. XML Storage: “Regions Index” • not user defined, default component of XML storage layer • maps nodeIDs to regions & pages • allows to fetch required regions instead of full documents • allows intelligent prefetching Regions index page page page

    11. XML Schema Support & Validation in DB2 • Use of XML Schemas is optional, on a per-document basis • No need for a fixed schema per XML column • Validation per document (i.e. per row) • Zero, one, or many schemas per XML column • For example: different versions of the same schema, or schemas with conflicting definitions • Mix validated & non-validated documents in 1 XML column • Schemas are registered & stored in the DB2 Schema Repository (XSR) for fast and stable access.

    12. Validation using Schemas Validate XML from a parameter marker using xsi:schemaLocation: insert into dept(deptdoc) values (xmlvalidate(?)) Override schema location by referencing a schema ID or URI: • insert into dept(deptdoc) values ( • xmlvalidate(? according to xmlschema id departments.deptschema) • insert into dept(deptdoc) values ( • xmlvalidate(? according to xmlschema uri 'http://my.dept.com’) Identify schema for a given document: select deptid, xmlxsrobjectid(deptdoc) from dept where deptid = “PR27”

    13. XML Indexes for High Query Performance • Define 0, 1 or multiple XML Value Indexes per XML column • XML index maps: (pathID, value)  (nodeID, rowID) • Index any elements or attributes, incl. mixed content • Index definition uses an XML pattern to specify which elements/attributes to index (and which not to) • Can index all elements/attributes, but not forced to do so • Can index repeating elements 0 , 1 or multiple index entries per document • New XML-specific join and query evaluation methods, evaluate multiple predicates concurrently with minimal index I/O xmlpattern = XPath without predicates, only child axis (/) and descendent-or-self axis (//)

    14. <dept bldg=101> <employee id=901> <name>John Doe</name> <phone>408 555 1212</phone> <office>344</office> </employee> <employee id=902> <name>Peter Pan</name> <phone>408 555 9918</phone> <office>216</office> </employee> </dept> XML Indexing: Examples create table dept(deptID char(8) primary key, deptdocxml); create index idx1 on dept(deptdoc) generate key using xmlpattern '/dept/@bldg' as sql double; create unique index idx2 on dept(deptdoc) generate key using xmlpattern '/dept/employee/@id' as sql double; create index idx3 on dept(deptdoc) generate key using xmlpattern '/dept/employee/name' as sql varchar(35); …xmlpattern '//name' as sql varchar(35); (Index on ALL “name” elements) …xmlpattern '//@*' as sql double; (Index on ALL numeric attributes) …xmlpattern '//text()‘ as sql varchar(hashed); (Index on ALL text nodes, hash code) …xmlpattern ‘/dept//name' as sql varchar(35); …xmlpattern '/dept/employee//text()' as sql varchar(128); (All text nodes under employee) …xmlpattern 'declare namespace m="http://www.myself.com/"; /m:dept/m:employee/m:name‘ as sql varchar(45);

    15. Querying XML Data in DB2 The following options are supported: • XQuery/XPath as a stand-alone language • SQL embedded in XQuery • XQuery/XPath embedded in SQL/XML • Plain SQL for full-document retrieval Compiler/Optimizer Details: Beyer et al. “System RX”, SIGMOD 2005 [2]

    16. Example: XQuery as a stand-alone Language in DB2 create table dept(deptID char(8) primary key, deptdocxml); for $d in db2-fn:xmlcolumn(‘dept.deptdoc’)/dept let $emp := $d//employee/name where $d/@bldg = > 95 order by $d/@bldg return <EmpList> {$d/@bldg, $emp} </EmpList> db2-fn:xmlcolumn returns the sequence ofall documents in the specified XML column <dept bldg=101> <employee id=901> <name>John Doe</name> <phone>408 555 1212</phone> <office>344</office> </employee> <employee id=902> <name>Peter Pan</name> <phone>408 555 9918</phone> <office>216</office> </employee> </dept>

    17. Examples: SQL embedded in XQuery create table dept(deptID char(8) primary key, deptdocxml); • Identify XML data by a SELECT statement • Leverage predicates/indexes on relational columns for $d in db2-fn:sqlquery('select deptdoc from dept(single document) where deptID= “PR27” ')… for $d in db2-fn:sqlquery('select deptdoc from dept(some documents) where deptIDLIKE “PR%” ')… for $d in db2-fn:sqlquery('select dept.deptdoc from dept, unit(some documents) where dept.deptID=unit.ID and unit.headcount > 200’)….. for $d in db2-fn:xmlcolumn(‘dept.deptdoc’)/dept , $e in db2-fn:sqlquery('select xmlforest(name, desc) from unit u’)… (constructed documents) (join & combine XML and relational data)

    18. Example: XQuery embedded in SQL/XML SQL/XML Standard Functions: xmlexists, xmlquery, xmltable create table dept(deptID char(8) primary key, deptdocxml); select deptID, xmlquery(‘for $i in$d/dept let $j := $i//name return $j’ passing deptdoc as “d”) from dept where deptIDLIKE “PR%”and xmlexists(‘$d/dept[@bdlg = 101]’ passing deptdoc as “d“)

    19. Other Features in DB2 native XML • XML Text Search Support • XML Import/Export • XML Type in Stored Procedures • API Extensions (JDBC, CLI, .NET, etc.) • XML Schema Repository • Full SQL/XML support • Visual XQuery Builder • Annotated schema shredding • …and more

    20. Summary CLOB and shredded XML storage restrict performance and flexibility New native XML support in DB2: • Better Performance through • Hierarchical & parsed XML representation at all layers • Path-specific XML Indexing • New XML join and query methods • Higher Flexibility through: • Integration of SQL and XQuery • Schemas are optional, per document, not per column • Zero, one, or many XML schemas per XML column

    21. Questions? mnicola@us.ibm.com

    22. BACKUP CHARTS

    23. Shredding: A simple case <DEPARTMENT deptid="15" deptname="Sales"> <EMPLOYEE> <EMPNO>10</EMPNO> <FIRSTNAME>CHRISTINE</FIRSTNAME> <LASTNAME>SMITH</LASTNAME> <PHONE>408-463-4963</PHONE> <SALARY>52750.00</SALARY> </EMPLOYEE> <EMPLOYEE> <EMPNO>27</EMPNO> <FIRSTNAME>MICHAEL</FIRSTNAME> <LASTNAME>THOMPSON</LASTNAME> <PHONE>406-463-1234</PHONE> <SALARY>41250.00</SALARY> </EMPLOYEE> </DEPARTMENT>

    24. Shredding: A schema change… “Employees are now allowed to have multiple phone numbers…” <DEPARTMENT deptid="15" deptname="Sales"> <EMPLOYEE> <EMPNO>10</EMPNO> <FIRSTNAME>CHRISTINE</FIRSTNAME> <LASTNAME>SMITH</LASTNAME> <PHONE>408-463-4963</PHONE> <PHONE>415-010-1234</PHONE> <SALARY>52750.00</SALARY> </EMPLOYEE> <EMPLOYEE> <EMPNO>27</EMPNO> <FIRSTNAME>MICHAEL</FIRSTNAME> <LASTNAME>THOMPSON</LASTNAME> <PHONE>406-463-1234</PHONE> <SALARY>41250.00</SALARY> </EMPLOYEE> </DEPARTMENT> • Requires: • Normalization of existing data ! • Modification of the mapping • Change of applications Costly!

    25. Native XML in DB2: Key Themes • Standards compliant + driving the standards • XML, XQuery, SQL/XML, XML Schema… • Flexibility, because that is what XML is all about.. • Zero, one, or many XML schemas per XML column • Native (hierarchical) Storage & Sophisticated XML Indexes • New “pivot join” to evaluate many predicates concurrently • Integrated in DB2 • Leveraging scalability, reliability, performance, availability… • Integrated with application APIs: • JDBC, ODBC, .NET, embedded SQL, CLI,… • Integrated with SQL • Access relational data and XML data in same statement

    26. VARCHAR (HASHED) DOUBLE DATE TIMESTAMP / text() // @attribute-tag element-tag / @* * // XML Index DDL index-name CREATE INDEX UNIQUE • create index idx1 on T(xmlcol) generate key using xmlpattern '/a/b/@c' as sql date; • Declaration & use of namespace prefix supported (not shown above) ON table-name(xml-column-name) GENERATE KEY USING xmlpattern xmlpattern = XPath without predicates, only child axis (/) and descendent-or-self axis (//) AS SQL VARCHAR (integer) xmlpattern: