Lifecycle Metadata for Digital ObjectsWhat is the XML environment?Review of “orders” of dataRemember, XML “does” nothingXML can enable action: RSSXML in two wrapper modesWhy mark up the object itself?Why not mark up the object?Best of both worldsXML Syntax rules for well-formed XML*Structure of the XML Document*XML DeclarationDocument type declarationXML document elementsAttributes of XML elementsGeneral entities in the XML documentMiscellaneous markupNamespaces in the XML documentThe DTDElement declarations in the DTDAttribute declarations in the DTDEntity declarations in the DTDXML Tools for home useAmaya screenshotXML Cooktop editor screenshotHow does all this relate to databases?Exercise 1: Assemble toolsExercise 2: Mark something upLifecycle Metadata for Digital ObjectsOctober 2, 2006Implementing Metadata in XMLWhat is the XML environment?XML editor (XML editors can’t do anything automatic until you load a DTD or schema; but you can edit XML in any plain-text editor)XML parser (at a minimum; while XML must be well-formed, it does not have to be validated; available in some browsers)Display program (e.g. browser)DTD or schema to define elementsStyle sheet for display of elementsXSLT engine to convert to other formats (e.g. database, webpage)Review of “orders” of dataFirst-order: language (segmentation)Second-order: encodingThird-order: meaningFourth order: groups of 3 and/or 4Fifth order: functionNote that each order is “meta” with respect to the one below and “data” with respect to the one above (cf. Goedel)Hence you “mark up” the order you wish to objectivize and access (examples: TEI, EAD)Remember, XML “does” nothingXML is not proceduralXML structures informationXML can store information (but is not random-access)XML can be a package for sending informationXML can be part of a solution for formatting informationXML can enable action: RSSTo add an RSS feed:First create the information you want to feed in XMLThen get yourself harvested!Further information and other examples of XML in action from Libby PeterekXML in two wrapper modesThe XML document as metadata repositoryXML document contains all the metadata Objects themselves are in separate files pointed to by the document (XLinks)The XML document as the whole enchiladaObject is marked up in XML tooMetadata is added as additional elements to the original objectIs this always a good idea?Why mark up the object itself?The object is a textThe text is well-formed as a hierarchical structure (problem of overlaps not solved in XML)Advantage is that the object carries its own metadataWhy not mark up the object?The object is not a text!The object is a text, but the text is too complex to mark up in XML (hierarchical model doesn’t suit everything; “overlap” problem)Best of both worldsXML metadata tags for human-readable packagingXML metadata loaded into database for random-access processing(Text) object version marked up in XML as relevantOriginal (text) object and derivative(s) pointed to in separate file(s) for preservationXML Syntax rules for well-formed XMLAn element containing text or elements must have start and end tagsAn empty element’s single tag must have a slash (/) before the end bracketAll attribute values must be in quotesElements may not overlapIsolated markup characters may not appear in parsed contentElement names may not use all characters (some are forbidden), and case is significant*Structure of the XML Document*Document prologueXML declarationDocument type declarationPoints to root elementPoints to external standards (DTDs, namespaces)Lists special internally-defined elements and general entitiesDocument itselfBracketed by root element tags at beginning and endContains elements, attributes, entitiesNested, hierarchical structureXML DeclarationGives version of XML<?xml version=“1.0”?>Defines character encoding (optional)<?xml version=“1.0” encoding=“UTF-8”?>Indicates presence of other needed files (optional)<?xml version=“1.0” encoding=“UTF-8” standalone=“no”?>Document type declarationPoints first to root element<!DOCTYPE example>Then points to any extern a l source for definition of document structure (that is, a DTD or schema), either a local separate file pathname (SYSTEM) or the URL for a file on the network (PUBLIC)<!DOCTYPE example SYSTEM “c:\My Documents\classes\metadata\example.dtd”…>Then adds any overriding local elements or entities (internal subset) in square bracketsXML document elementsElements don’t need to be declared except to overrride DTDElements contain information (element tags simply bracket information)<name attribute=value>chardata</name>Empty elements (no data is contained, begin and end element tags are collapsed to one)<name attribute=value />Attributes of XML elementsElements don’t require attributes; some functions can be achieved by nesting subelements within elementsUsed to provide more details about an element; used to split off groups of elements for particular purposes (e.g., layout, search) <elementname attname=“value”>General entities in the XML documentExternal entities (e.g., imported text or other object) must be declared in document prologueThe “entity” behaves something like a “variable”; once defined, value can be referencedWithin the document, the entity name is used preceded by an ampersand:<greeting> Dear &name, </greeting>When the document is displayed or used, the entity value at the time will be substituted for the nameMiscellaneous markup<!--Comments--><![CDATA[Contains#$*^%*&%otherwise forbidden]]><?processinginstruction data?>Namespaces in the XML documentNamespaces must be declared before use: xmlns:name=“URI” then elements from namespace can be used in document as: <name:element>….</name:element>Scope is the element within which namespace is declared, plus descendant nodesNamespaces cannot be validated with a DTDThe DTDDocument Type Definition; not actually expressed in XMLProvides a lexicon of allowed elements and attributes for the XML document that refers to itDefines a content model for each elementLike declaration of data types in a programming language; allows you to define your own types (a private, or