1 / 30

XML Schemas in Oracle XML DB

XML Schemas in Oracle XML DB. Ravi Murthy Sandeepan Banerjee Oracle Corporation. Talk Overview. Why XML in DB ? Background XML Schema Object-Relational DB XML Schema Support in Oracle XML DB XML Storage XML Query XML Update Future directions and Conclusions. Why XML in DB ?.

mckile
Download Presentation

XML Schemas in Oracle XML DB

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. XML Schemas in Oracle XML DB Ravi Murthy Sandeepan Banerjee Oracle Corporation

  2. Talk Overview • Why XML in DB ? • Background • XML Schema • Object-Relational DB • XML Schema Support in Oracle XML DB • XML Storage • XML Query • XML Update • Future directions and Conclusions

  3. Why XML in DB ? • Trends in industry • More XML content being generated • More applications dealing with (structured) data and (semi-structured) documents • Need for unified management for all kinds of data • XML Schema language provides strong typing • Many benefits to storing XML in DB • Better Queriability • Optimized Updates • Stronger Validation • Fidelity of XML very important

  4. Oracle XML DB Overview • Native XML data type • Supports W3C XML Schema data model • XML/SQL Duality • Support for XML standards • Namespaces, XPath, XSLT, SQL/XML • High performance XML repository • Hierarchical File System Abstraction • Protocols : FTP, HTTP/WebDAV • Access Control (ACL) • Versioning

  5. XML Schema • W3C Recommendation • Large number of built-in scalar data types • Simple type definitions • Length, pattern and other constraints • Complex type definitions • sequence / choice / all • Mixed content • Extensible • Derivation by extension and restriction • Substitution Groups • Wildcards • Gradually replacing the traditional DTD • Commonly used as a validation mechanism

  6. Object Relational DB Basics • Object types • Collection types • Object References • LOBs

  7. XMLType • Native data type for XML • Used to define columns of tables and views, arguments to stored procedures, etc. • XML specific methods and operators for • Querying and extracting XML using XPath • Transforming XML using XSLT • Validating XML using XML Schema • Multiple Storage Options • Unstructured Storage in CLOB • Structured Storage into object-relational rows and columns • Hybrid Storage • Maintains application transparency to physical storage choice

  8. XML DB and XML Schema • XML Schema controls all aspects of processing • Storage mappings • In-memory representations • Language Bindings • XML Schema Registration Process • Associates XML Schema with URL • Generates Object types • Creates default tables • XMLType column can be constrained to a global element of registered schema

  9. XML Schema Example <schema targetNamespace=“http://www.oracle.com/PO.xsd” xmlns:po=“http://www.oracle.com/PO.xsd” elementFormDefault=”qualified” xmlns="http://www.w3.org/2001/XMLSchema"> <complexType name="PurchaseOrderType"> <sequence> <element name="PONum" type="decimal"/> <element name="Company"> <simpleType> <restriction base="string"> <maxLength value="100"/> </restriction> </simpleType> </element>

  10. XML Schema Example (contd) <element name="Item" maxOccurs="1000"> <complexType> <sequence> <element name="Part"> <simpleType> <restriction base="string"> <maxLength value="1000"/> </restriction> </simpleType> </element> <element name="Price" type="float"/> </sequence> </complexType> </element> </sequence> </complexType> <element name="PurchaseOrder" type="po:PurchaseOrderType"/> </schema>

  11. Generated Object Types TYPE "Item_T" (part varchar2(1000), price number); TYPE "Item_COLL" AS VARRAY(1000) OF "Item_T"; TYPE "PurchaseOrderType_T" (ponum number, company varchar2(100), item Item_COLL);

  12. Generated Tables TABLE po_tab OF XMLTYPE XMLSCHEMA “http://www.oracle.com/PO.xsd" ELEMENT "PurchaseOrder“ VARRAY(item) STORE AS item_tab;

  13. XML Document Example <PurchaseOrder xmlns="http://www.oracle.com/PO.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.oracle.com/PO.xsd http://www.oracle.com/PO.xsd"> <PONum>1001</PONum> <Company>Oracle Corp</Company> <Item> <Part>9i Doc Set</Part> <Price>2550</Price> </Item> <Item> <Part>8i Doc Set</Part> <Price>350</Price> </Item> </PurchaseOrder>

  14. XML Storage – PO_TAB and LINE_TAB

  15. Structured Storage • Attributes and single-valued elements • Stored as columns in single row • SQL data types correspond to XML Schema types • SQL constraints correspond to XML Schema constraints • Multi-valued elements (collections) stored in separate nested tables • One row per item in collection • Nested table row stores parent key • Array Index column stores the position information • Number column – uses full range of floating points • Elements inserted in the middle of the collection get (previous_array_index + next_array_index)/2 • Supports multiple levels of nesting • Embedded object types • Embedded collection types with multiple nested tables

  16. DOM Fidelity • Structured storage guarantees DOM fidelity • No whitespace fidelity • System binary attribute in object types • SYS_XDBPD$ • PD attribute stores non-relational information • Ordering of elements • Comments • Processing Instructions • Namespace declarations • Prefix information • Mixed content – text nodes that are intermixed with elements are stored in the system column

  17. XDB Attributes in XML Schema • Mapping details captured as new attributes within the XML Schema • Oracle attributes use namespace : http://xmlns.oracle.com/xdb • Input XML Schema does not need to be annotated • Default assumptions for all XDB attributes • Input XML Schema can explicitly specify XDB attributes • SQLName : Name of column or type attribute • SQLType : Name of object type • SQLCollType : Name of collection type • MaintainOrder : Permits turning off order maintenance

  18. Hybrid Storage of XML • Two ends of storage spectrum • Store entire content in a single LOB • Full shredding of XML data • Hybrid Storage Options • Combination of shredding and LOB storage • xdb:SQLType=“CLOB” applied to <complexType> • CLOB storage ideal for fragments that are not intended for query or partial updates • Example : XHTML content embedded within resource descriptors (metadata)

  19. Querying XMLType • XPath based operators • existsNode • Boolean operator • Checks for existence of node identified by XPath • extract • Extracts a fragment identified by XPath • extractValue • Retrieves the raw value of leaf node identified by XPath • Namespace Aware • ANSI SQL/XML Standards effort

  20. Query Rewrite • Automatic rewrite of XPaths during query compilation • Rewritten query directly accesses underlying relational columns • Introduces joins with nested tables • Enables use of indexes

  21. Query Rewrite - Example • Original Query SELECT extractValue(value(p), '/PurchaseOrder/PONum') FROM po_tab p WHERE existsNode(value(p), '/PurchaseOrder[Company=Oracle]') = 1; • Rewritten Query SELECT p.ponum FROM po_tab p WHERE p.company = 'Oracle';

  22. Query Rewrite Examples

  23. Updating XMLType • Updating entire XML document • Partial Update • Uses UpdateXML() operator • XPath identifies element or attribute to be updated • New value for the updated node is specified • Rewritten to directly update underlying column(s) • Similar mechanisms for • Inserting new nodes • Deleting node(s)

  24. Update Rewrite - Example • Original Statement UPDATE po_tab p SET value(p) = updatexml(value(p), '/PurchaseOrder/PONum/text()', 9999) WHERE existsNode(value(p), ‘/PurchaseOrder[Company=Oracle]’) = 1; • Rewritten Statement UPDATE po_tab p SET p.ponum = 9999 WHERE p.Company = ‘Oracle’;

  25. XMLType Views • Provide an XML view of relational data • Good evolutionary strategy • New XML apps on XML abstraction of existing data • SQL/XML Standard operators used to generate XML • Views can generate schema based XML • Insert / Update / Delete operations via ‘Instead of’ Triggers • Queries over XML views are rewritten to directly access underlying relational columns

  26. XMLType View - Example CREATE VIEW po_view of XMLTYPE XMLSCHEMA "po.xsd" ELEMENT "PurchaseOrder" AS SELECT XMLElement("PurchaseOrder", XMLForest(p.ponum "PONum", p.company "Company"), (SELECT XMLAGG( XMLElement("Item", XMLForest(i.part "Part", i.price "Price")) FROM items_rel_tab i WHERE i.po_id = p.id)) FROM po_rel_tab p;

  27. Complex XML Schemas • Cyclic Definitions • Object types created with references • Table row contains reference to other rows stored in same or different table • Keys to document and parent rows stored in nested rows • Complex type derivation • Mapped to object type inheritance • Wildcards • Mapped to CLOB attributes

  28. Indexing XMLType • Multiple index types • B-Tree and bitmap indexes • Function-based indexes • Create index on specific XPath expressions • Text indexes • Inverted lists provide section-based search • Also support keyword based search within textual content

  29. Future Directions • Optimize XML Query support • Translate XML Query to SQL • Works against distributed databases using Oracle connectivity solutions • Optimize support for highly variable documents • New storage and indexing techniques

  30. Conclusions • Oracle XML DB is a robust platform for building XML applications • Strong support for XML Schema based storage, query, indexing and updates • Structured storage maintains XML fidelity • Support for standards such as SQL/XML, XPath and XSLT • Powerful XML/SQL Duality

More Related