With Oracle XML DB, you can store and manage data that is structured, unstructured, and semi-structured using a standard data model and standard SQL and XML. You can perform SQL operations on XML documents and XML operations on object-relational (such as table) data.

Most application data and Web content is stored in a relational database, a file system, or both. XML data is often used for data exchange, and it can be generated from a relational database or a file system. As the volume of XML data exchanged grows, the cost of regenerating this data grows, and these storage methods become less effective at accommodating XML content.

Figure 1-2 Unifying Data and Content: Some Common XML Architectures

Description of "Figure 1-2 Unifying Data and Content: Some Common XML Architectures"

Organizations often manage their structured data and unstructured data differently:

• Unstructured data, stored in tables, makes document access transparent and table access complex.

• Structured data, often stored in binary large objects (such as in BLOB instances), makes access more complex and table access transparent.

• Database Capabilities for Working with XML
  Oracle Database provides database capabilities for working with XML: indexing and search; updates and transaction processing; managing relationships using constraints; multiple data views; high performance and scalability. It supports XML Schema, XQuery, XPath, and DOM.
• Advantages of Storing Data as XML in the Database
  Storing data as XML in the database provides these advantages: storage independence, ease of presentation, and ease of interchange.

Oracle XML DB presents a symmetric, dual view of data: as XML and as relational.

A key feature of Oracle XML DB is that it lets you work with XML data as if it were relational data and relational data as if it were XML data. You can leverage the power of the relational model when working with XML content, and you can leverage the flexibility of XML when working with relational content. You can use the most appropriate tools for different aspects of a particular business problem.

This duality means that the same data can be exposed as rows in a table and manipulated using SQL or exposed as nodes in an XML document and manipulated using XQuery, the DOM, or XSL transformation. Access and processing techniques are independent of the underlying storage method.

These features can provide simple solutions to common business problems:

• You can generate XML data directly from a SQL query. You can transform the XML data into other formats, such as HTML, using the database-resident XSLT processor.

• You can access XML content without converting between different data formats, using SQL queries, on-line analytical processing (OLAP), and business-intelligence/data warehousing operations.

• You can perform text and spatial data operations on XML content.

• Use XMLType Views If Your Data Is Not XML
  XMLType views provide a way for you to wrap existing relational or object-relational data in XML format.

Oracle XML DB provides high performance and scalability for XML operations, letting you manage the storage and retrieval of complex, large, or many XML documents.

These are the major performance features of Oracle XML DB:

• Native XMLType. Abstract data type XMLType has two storage models, each optimized to work efficiently for a particular set of use cases. See Query and Update of XML Data and Choice of XMLType Storage and Indexing

• Optimized processing of XQuery, XPath, and XSLT. See Performance Tuning for XQuery and Transformation and Validation of XMLType Data.

• Indexing XML data for structured or full-text search. See Indexes for XMLType Data.

• A lazily evaluated virtual DOM. See PL/SQL DOM API for XMLType (DBMS_XMLDOM).

• A hierarchical index over Oracle XML DB Repository. See Performance Guidelines for Oracle XML DB Repository Operations.

• Parallelism and Oracle Exadata Smart Scan. Query and update of XML data can be carried out in parallel. Oracle Exadata Smart Scan is enabled automatically for XML data.

Using XMLType, XML developers can leverage the power of XML standards while working in the context of a relational database, and SQL developers can leverage the power of a relational database while working with XML data.

XMLType is an abstract native SQL data type for XML data. It provides PL/SQL and Java constructors for creating an XMLType instance from a VARCHAR2, CLOB, BLOB, or BFILE instance. And it provides PL/SQL methods for various XML operations.

You can use XMLType as you would any other SQL data type. For example, you can create an XMLType table or view, or an XMLType column in a relational table.

You can use XMLType in PL/SQL stored procedures for parameters, return values, and variables.

You can also manipulate XMLType data using application programming interfaces (APIs) for the Java and C languages, including Java Database Connectivity (JDBC), XQuery for Java (XQJ), and Oracle Data Provider for .NET (ODP.NET).

XMLType is an Oracle Database object type, so you can also create a table of XMLType object instances. By default, an XMLType table or column can contain any well-formed XML document.

You can constrain XMLType tables or columns to conform to an XML schema, in which case the database ensures that only XML data that validates against the XML schema is stored in the column or table. invalid documents are excluded.

XMLType is an abstract data type that provides different storage models to best fit your data and your use of it. As an abstract data type, your applications and database queries gain in flexibility: the same interface is available for all XMLType operations.

XMLType tables and columns can be stored in these ways:

• Binary XML storage (the default) – XMLType data is stored in a post-parse, binary format designed specifically for XML data. Binary XML is compact, post-parse, XML schema-aware XML data. This is also referred to as post-parse persistence.

• Object-relational storage – XMLType data is stored as a set of objects. This is also referred to as structured storage and object-based persistence.

With the use of appropriate indexes, binary XML storage offers good performance for most use cases. However, some advanced use cases can benefit from using object-relational storage.

You can change XMLType storage from one model to another using database import/export. Your application code need not change. You can change XML storage options when tuning your application.

For binary XML storage, SecureFiles is the default storage option.^Foot 1 However, if either of the following is true then it is not possible to use SecureFiles LOB storage. In that case, BasicFiles is the default option for binary XML data:

• The tablespace for the XMLType table does not use automatic segment space management.

• A setting in file init.ora prevents SecureFiles LOB storage. For example, see parameter DB_SECUREFILE.

Support for the World Wide Web Consortium (W3C) XML Schema Recommendation is a key feature in Oracle XML DB.

XML Schema specifies the structure, content, and certain semantics of XML documents. It is described in detail at http://www.w3.org/TR/soap12-part0/.

The W3C Schema Working Group publishes a particular XML schema, often referred to as the schema for schemas, that provides the definition, or vocabulary, of the XML Schema language. An XML schema definition (XSD^Foot 2), also called an XML schema, is an XML document that is compliant with the vocabulary defined by the schema for schemas.

An XML schema uses vocabulary defined by the schema for schemas to create a collection of XML Schema type definitions and element declarations that comprise a vocabulary for describing the contents and structure of a new class of XML documents, the XML instance documents that conform to that XML schema.

The XML Schema language provides strong typing of elements and attributes. It defines numerous scalar data types. This base set of data types can be extended to define more complex types, using object-oriented techniques such as inheritance and extension. The XML Schema vocabulary also includes constructs that you can use to define complex types, substitution groups, repeating sets, nesting, ordering, and so on. Oracle XML DB supports all of the constructs defined by the XML Schema Recommendation, except for redefines.

XML schemas are commonly used as a mechanism for checking (validating) whether XML instance documents conform with their specifications. Oracle XML DB includes XMLType methods and SQL functions that you can use to validate XML documents against an XML schema.

In Oracle XML DB, you can use a standard data model for all of your data, regardless of how structured it is. You can use XML Schema to automatically create database tables for storing your XML data. XML schema-based data maintains DOM fidelity and allows for significant database optimizations.

XML schema-based data can be stored using either Oracle XML DB XMLType storage model: binary XML storage or object-relational storage. Non-schema-based XML data can be stored only using binary XML storage.

You can also wrap existing relational and object-relational data as XMLType views, which can optionally be XML schema-based. You can map from incoming XML documents to XMLType storage, specifying the mapping using a registered XML schema.

An XML schema is in general a much more powerful way to define XML document structure than is a DTD. You can nevertheless use DTDs to some extent with Oracle XML DB.

Like an XML schema, A DTD is a set of rules that define the allowable structure of an XML document. DTDs are text files that derive their format from SGML. They can be associated with an XML document by using DTD element DOCTYPE or by using an external file through a DOCTYPE reference.

Oracle XML DB uses XML Schema, not DTDs, to define structured mappings to XMLType storage, but XML processors can still access and interpret your DTDs.

Several static data dictionary views are related to XML.

DESCRIBE USER_XML_SCHEMAS

Oracle XML DB provides the SQL functions that are defined in the SQL/XML standard.

SQL/XML functions fall into two groups:

• Functions that you can use to generate XML data from the result of a SQL query. In this book, these are called SQL/XML publishing functions. They are also sometimes called SQL/XML generation functions.

• Functions that you can use to query and update XML content as part of normal SQL operations. In this book, these are called SQL/XML query and update functions.

Using SQL/XML functions you can address XML content in any part of a SQL statement. These functions use XQuery or XPath expressions to traverse the XML structure and identify the nodes on which to operate. The ability to embed XQuery and XPath expressions in SQL statements greatly simplifies XML access.

All Oracle XML DB functionality is accessible from C, PL/SQL, and Java.

You can build Web-based applications that take advantage of Oracle XML DB in various ways, including these:

• Using servlets and Java Server Pages (JSP). A typical API accesses data using Java Database Connectivity (JDBC).

• Using Extensible Stylesheet Language (XSL) plus XML Server Pages (XSP). A typical API accesses data in the form of XML documents that are processed using a Document Object Model (DOM) API implementation.

Oracle XML DB supports such styles of application development. It provides Java, PL/SQL, and C implementations of the DOM API. Applications that use JDBC, such as those based on servlets, need prior knowledge of the data structure they are processing. Oracle JDBC drivers allow you to access and update XMLType tables and columns, and call PL/SQL procedures that access Oracle XML DB Repository. Applications that use DOM, such as those based on XSLT transformations, typically require less knowledge of the data structure. DOM-based applications use string names to identify pieces of content, and must dynamically walk through the DOM tree to find the required information. For this, Oracle XML DB supports the use of the DOM API to access and update XMLType columns and tables. Programming to a DOM API is more flexible than programming through JDBC, but it may require more resources at run time.

Oracle XML DB Repository is a component of Oracle Database that lets you handle XML data using a file/folder/URL metaphor.

Oracle XML DB Repository contains resources, which can be either folders (directories, containers) or files.

A resource, whether folder or file, has these properties:

• It is identified by a path and name.

• It has content (data), which can be XML data but need not be.

• It has a set of system-defined metadata (properties), such as Owner and CreationDate, in addition to its content. Oracle XML DB uses this information to manage the resource.

• It might also have user-defined metadata. Like system-defined metadata, this is information that is not part of the content, but is associated with it.

• It has an associated access control list that determines who can access the resource, and for what operations.

Although Oracle XML DB Repository treats XML content specially, you can use the repository to store other kinds of data besides XML. You can use the repository to access any data that is stored in Oracle Database.

You can access data in the repository in the following ways:

• SQL – Using views RESOURCE_VIEW and PATH_VIEW

• Standard protocols – FTP, HTTP(S), and WebDAV

• PL/SQL – Using PL/SQL package DBMS_XDB_REPOS

• Java – Using the Oracle XML DB resource API for Java

Besides providing APIs for accessing and manipulating repository data, Oracle XML DB provides APIs for the following repository services, which are based on IETF WebDAV:

• Versioning – Using PL/SQL package DBMS_XDB_VERSION

• ACL Security – Using access control lists (ACLs)

• Foldering – Using repository path names

Figure 1-4 illustrates the architecture of Oracle XML DB Repository.

Figure 1-4 Oracle XML DB Repository Architecture

Description of "Figure 1-4 Oracle XML DB Repository Architecture"