XML STORAGE AND XPATH QUERIES IN ORACLE Jiankai Wu & Joel Poualeu

Outline 1. XML type storage models 2. How to decide selection of models 3. Example of creating XML type table 4. XPath Addressing 5. XPath Expressions 6. XPath Data Types, Operators and Functions

XMLType Storage Models Unstructured storage referred to as CLOB(Character Large Object) storage and text-based persistence. Structured storage referred to as object-relational storage and object-based persistence.

Structure storage

How to decide Data-centric XML documents Document-centric XML documents Hybrid XML documents

Data-centric Data is highly structured, with relatively static and predictable structure Example: an employee record (fields employee number, name, address, and so on) Employ object-relational (structured) storage

registers a XML schema BEGIN DBMS_XMLSCHEMA.REGISTERSCHEMA ( SCHEMAURL => ' SCHEMADOC => BFILENAME('XML_DIR','OracleXMLSchema.xsd'), GENTABLES => FALSE, csid => NLS_CHARSET_ID('AL32UTF8')); END; / PL/SQL PROCEDURE successfully completed.

create the schema based XML Type table CREATE TABLE xml_demo_structured OF XMLTYPE xmlschema " localhost/Oraxdb/OracleXMLSchema.xsd" ELEMENT "EmployeeDetails" / TABLE created

Insert a sample XML Type data in the table INSERT INTO xml_demo_structured VALUES (xmltype(BFILENAME('XML_DIR', 'Allen.txt'), NLS_CHARSET_ID('AL32UTF8'))) / 1 ROW inserted. sample text file Allen.txt

Document-centric Data is generally without structure or of variable structure Content is mixed--elements contain large amounts of text Stored or fetched as a complete document Employ CLOB-based(unstructured) storage

creation of a table of XMLType 1. CREATE TABLE xml_demo_unstructured OF XMLTYPE 2. xmltype STORE AS clob 3. / TABLE created.

Structured (object-relational) storage Optimized memory management Reduced storage requirements B-tree indexing Structural flexibility is reduced Unstructured (CLOB) storage Easy to insert and retrieve entire XML document No data conversion is needed

Hybrid storage The mixture of structured and unstructured storage Example: an employee record that includes a free-form resume

XPATH Addresses an XML document’s elements and attributes. Addressing is similar to file system addressing (/) is a path separator. (/) starts An absolute path from the root Relative path starts with anything else. (..) indicates the parent of the current node. (.) indicates the current node. Attributes are specified prefix. [ ] can further specify an element.

Xpath Addressing Example Hello world! ExpressionResult a/bselect elements children of elements /a/b/c"Hello world!" "$56"

Xpath Expression Example not available Soap 33 Milk 56 ExpressionResult /inventory/item[2]/nameMilk /inventory/item/name[2]null

XPath Data Types and Operators and functions XPath expressions yield either a set of nodes, a string, a Boolean (a true/false value), or a number |+, -, *, div, mod,, = Supported functions substring-before(string1, string2) substring-after(string1, string2) translate(string1, string2, string3) normalize-space()

References "How XPath Works." Oracle Documentation. N.p., n.d. Web. 2 May "Introduction to Oracle XML DB." Oracle Documentation. N.p., n.d. Web. 2 May "XPath 2.0 Expression Syntax." The SAXON XSLT and XQuery Processor. N.p., n.d. Web. 2 May <