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XML documents have a hierarchical structure and can conceptually be interpreted as a tree structure, called an XML tree. XML documents must contain a root element (one that is the parent of all other elements). All elements in an XML document can contain sub elements, text and attributes.
Within the root element, apart from any number of attributes and other elements, there may also be more optional text, comments, processing instructions and whitespace. A more expanded example of an XML document follows, demonstrating some of these extra nodes along with a single rootElement element.
An XML attribute can only have a single value and each attribute can appear at most once on each element. In the common situation where a list of multiple values is desired, this must be done by encoding the list into a well-formed XML attribute [ i ] with some format beyond what XML defines itself.
The Document Object Model (DOM) is a cross-platform and language-independent interface that treats an HTML or XML document as a tree structure wherein each node is an object representing a part of the document. The DOM represents a document with a logical tree. Each branch of the tree ends in a node, and each node contains objects.
There is a single "root" element that contains all the other elements. A valid XML document is defined in the XML specification as a well-formed XML document which also conforms to the rules of a Document Type Definition (DTD). According to JavaCommerce.com XML tutorial, "Well formed XML documents simply markup pages with descriptive tags.
The vocabulary (element and attribute names) The content model (relationships and structure) The data types; This collection of information is called the Post-Schema-Validation Infoset (PSVI). The PSVI gives a valid XML document its "type" and facilitates treating the document as an object, using object-oriented programming (OOP) paradigms.
XML namespaces are used for providing uniquely named elements and attributes in an XML document. They are defined in a W3C recommendation. [1] [2] An XML instance may contain element or attribute names from more than one XML vocabulary. If each vocabulary is given a namespace, the ambiguity between identically named elements or attributes can ...
the effective value of the attribute can only be a valid identifier (or a space-separated list of such identifiers) and must be referencing the unique element defined in the document with an attribute declared with the type ID in the DTD (or the unique element defined in an XML document with a pseudo-attribute "xml:id") and whose effective ...