Xml data transformation
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XML was introduced as a metalanguage for data description that can be transformed into specific markup languages based on vocabulary and schema. An XML transformation expresses the semantics of a document using another equivalent syntax, similar to a type cast. XSLT is the rule-based language used to transform XML documents into other text formats through XSLT programs, using XPath queries to select parts of the XML document. The XSLT process combines an XML source file and style sheet to produce a third output document in XML, HTML, or other text format.
Xml data transformation
- 2. • XML was first introduced as a metalanguage for data description. • A metalanguage represents a well-defined interface that evolves and is transformed into derived languages. XML is simply the foundation interface for a number of specific markup languages, each of which is based on its own vocabulary and schema.
- 3. • The schema syntactically differentiates XML languages from each other. XML is key for data exchange and interoperability, and the schema is essential for providing XML documents with a typed and well-defined structure. Unfortunately, in the imperfect world in which we live, schemas often express the same semantics through different syntaxes.
- 4. • An XML transformation is simply the XML workaround for this relatively common situation. An XML transformation is a user-defined algorithm that attempts to express the semantics of a given document using another equivalent syntax. A transformation is much like a type cast in programming. You can always try to coerce the type, but in doing so you could face and accept compromises like syntax adaptations and, sometimes, loss of data and logic.
- 5. • In XML, the transformation process is seen as the application of a style sheet to the source document. The style sheet is a declarative and user-defined document that is referred to as extensible. The term Extensible Stylesheet Language (XSL) indicates a metalanguage designed for expressing style sheets for XML documents. An XSL file contains the set of rules that will be used to transform a document into another,
- 6. • XSL files were originally conceived as the XML counterpart of HTML's cascading style sheets (CSS). In this context, XSL files were simply extensible and user- definable tools to render an XML markup in HTML for display purposes. The growing complexity of style sheets, as well as the advent of XML schemas, changed the perspective of XSL and led to XSL Transformations (XSLT).
- 7. • The goal of XSL has evolved over time. Today, XSL is a blanket term for a number of derived technologies that altogether better qualify and implement the original idea of styling XML documents. The various components that fall under the umbrella of XSL are the actual software entities that you use in your code:
- 8. • XSLT Rule-based language for transforming XML documents into any other text-based format. XSLT provides for XML-to-XML transformation, which mostly means schema transformation. An XSLT program is a generic set of transformation rules whose output can be any text-based language, including HTML, Rich Text Format (RTF), and Wireless Markup
- 9. • XPath Query language that XSLT programs use to select specific parts of an XML document. The result of XPath expressions is then parsed and elaborated by the XSLT processor
- 10. • XSL Formatting Objects (XSL-FO) Advanced styling features expressed by • an XML vocabulary that define the semantics of a set of formatting • elements
- 11. XSLT TEMPLATE PROGRAMMING XSLT is a process that combines two XML documents—the XML source file and the style sheet—to produce a third document. The resultant document can be an XML document, an HTML page, or any text-based file the style sheet has been instructed to generate. The source document must meet only one requirement: it must be a well-formed XML document. The style sheet must be a valid XML document that contains the transformation logic expressed using the elements in the XSLT vocabulary. An XSLT style sheet can be seen as a sequence of templates.
- 12. AN OVERVIEW OF THE XSLT PROCESS
- 13. • The core part of the transformation process is the application of templates to XML source elements. Other ancillary steps might include the expansion of elements to text, the execution of some script code, and the selection of a subset of nodes using Xpath queries. The layout of a generic XSLT script is shown here:
- 14. • <xsl:stylesheet • xmlns:xsl="http://www.w3.org/1999/xsl/transform"> • <xsl:template match="/"> • ⋮ • </xsl:template> • <xsl:template match="..."> • ⋮ • </xsl:template> • ⋮ • </xsl:stylesheet>
- 15. • The final output of each template must form a syntactically valid fragment in the target • language—be it XML, HTML, RTF, or some other language. You are not required to • indicate the target language explicitly, although the XSLT vocabulary provides a tailormade • instruction to declare what the expected output will be. The main requirement for • the XSLT style sheet is that its overall text be well-formed XML. In addition, it must • make syntactically correct use of all the XSLT instructions it needs. The
- 16. APPLYING AN XSLT TEMPLATE TO SOURCE MARKUP TEXT.
- 17. XSLT INSTRUCTIONS • The XSLT vocabulary consists of special tags that represent particular operations you • can perform on the source markup text or passed arguments. Although the overall • syntax is that of a rigorous XML dialect, you can easily recognize the main constructs of a high-level programming language. • The following subsections summarize the main XSLT instructions you are likely to run • across in your XSLT experience. The XSLT instructions are divided into four categories:
- 19. THE STYLE SHEET IS FIRST NORMALIZED TO AN XPATH NAVIGATOR AND THEN COMPILED
- 20. MANAGING THE PROCESSOR'S STATE • The style sheet compiler populates three internal data structures with the data read from the source.