Notes Week 10

What Is XML?

·         Subset of the Standard Generalized Markup Language (SGML), easy to interchange structured docs over internet

·         Defines how Internet Uniform Resource Locators can be used to identify component parts of XML data streams

·         Document Type Definition: role of each element of text in a formal model, not required in XML

·         XML lets users bring mult files together to form compound docs, where to put pictures in text, give processing control info to supporting programs, add editorial comments

·         Composed of a series of entities, each one contains 1+ logical elements, each elements has certain attributes to describe how to be processed

·         To define tag sets use DTD

·         Some elements are placeholders, empty elements. No end-tag. Usually for graphic.

·         Important=unique identifier, cross reference between two points in doc

·         Text entity, commonly used text within DTD

·         XML file normally has three types of markup, first two option: processing instruction, document type declaration, document instance

Survey of XML standards

·         Builds on Unicode & DTD

·         XML 1.1 first revision, revise treatment of characters in the XML specification to make it adapt more naturally to changes in the Unicode specification & normalization of characters

·         Based on Standard Generalized Markup Language

·         XML Catalogs has instructions how XML processor resolves XML entity identifiers into actual documents. System identifiers given by URIs. Public Identifiers.

·         Namespaces in XML universal naming of elements and attributes in XML docs. Assign vocab markers if want to embed XHTML.

·         XML Base associating XML elements with URIs specify how relative URIs are resolved in relevant XML processing actions

·         Canonical XML Version 1.0 standard method for generating physical rep of an XML document, called canonical form. Accounts for variations allowed in XML syntax without changing meaning.

·         XML Path Language syntax/data model for addressing parts of an XML document, a little language

·         XPointer Framework defines a language to refer to fragments of an XML doc

·         XLink generic framework for expressing links in XML docs. Harder than in HTML.

·         Relax NG XML schema language, define and limit XML vocabs. Original is DTD, but some people dislike it while Relax is more simple/expressive.

·         W3C XML Schema another schema language for XML. First part constrains structure of doc, second constrains contents of simple elements and attributes.

·         Schematron schema language register collection of rules against which the XML doc is to be checked rather than mapping out entire tree structure

Extending Your Markup

·         Looks like HTML docs, starts with a prolog, ends with exactly one element

·         Single element can be viewed as root of doc, build off from there

·         DTD declared in XML doc’s prolog with !DOCTYPE tag

·         Elements nonterminal or terminal. Nonterminal contain subelements, grouped as sequences or choices. Terminal elements as parsed character data or EMPTY. Elements declared as ANY.

·         Elements can have zero or more attributes, declared using !ATTLIST tag

·         Character data most common data type for attributes. Types id, idref, idrefs

·         Namespaces avoids names clashes, can be defined in any element. Define all namespaces within the root element and use unique prefixes. Namespaces and DTDs don’t work well together.

·         Xlink describes how 2 docs can be linked

·         XPointer enables addressing individual parts of an XML doc

·         XPath used by XPointer to describe location paths

·         Location path has location steps

·         XLink to link docs together, uses its own namespace

·         XSL is two languages: transformation language (XSLT) and formatting language.

·         XSLT can transform XML  into HTML, bypass formatting language

·         XML is family of lanugages

W3Schools XML

·         Greatest strength of XML Schemas is support for data types, they use XML Schemas so don’t have to learn new language, secures data communication

·         Well-formed XML doc is a doc that conforms to the XML syntax rules

·         Complex types, simple types

·         <schema> element root

·         Simple element contains only text, can’t have attributes