XML Standard for Data Encapsulation

XML: A New
Standard for Data
Daniel Stout
University of Iowa Libraries
30 May 2003

Find this presentation Online
n To find this presentation online, visit:
http://staffweb.lib.uiowa.edu/dstout/xml.htm
n Or will be up on Libraries Intranet

XML: What is it?
n Extensible Markup Language (XML)
n What’s a Markup Language?
¨Example: HTML–Hypertext Markup Language
¨It’s just a text file…
¨…which makes it easy to transfer on the Web.
n It has a variety of functions, such as…

What does XML do exactly?
n Standardized method for encapsulating data
and digital objects.
n It is a wrapper that goes around digital
information – text, images, video.
n XML can encode metadata…
n …but also can define the features of a document
(e.g. TOC, formatting)
n XML is a way to describe document structure –
like the structure of a book, for example.

XML is between the brackets
n It uses tags in brackets, just like HTML.
¨HTML example file:
<html>
<head>
<title>This is My Web Page</title>
</head>
<body background=“#FFFFFF”>
Hello, World!
</body>
</html>

XML can look very simple
n A very basic and valid XML file:
<?xml version="1.0"?>
<oldjoke>
<burns>Say <quote>goodnight</quote>,
Gracie.</burns>
<allen><quote>Goodnight,
Gracie.</quote></allen>
<applause />
</oldjoke>

A MARC Record in XML
<fixfield id="1">" 90178038 "</fixfield>
<fixfield id="3">"DLC"</fixfield>
<fixfield id="5">"19900814092959.1"</fixfield>
<fixfield id="8">"900724s1974 po af 000 0
fre "</fixfield>
<varfield id="10" i1=" " i2=" ">
<subfield label="a">90178038</subfield>
</varfield>
<varfield id="40" i1=" " i2=" ">
<subfield label="a">DLC</subfield>
<subfield label="c">DLC</subfield>
</varfield>

But XML can be complicated
n Less readable than HTML…
n …because it is more powerful.
<xml xmlns:v="urn:schemas-microsoft-com:vml"
xmlns:o="urn:schemas-microsoft-com:office:office"
xmlns:p="urn:schemas-microsoft-
com:office:powerpoint" xmlns:oa="urn:schemas-
microsoft-com:office:activation">
<p:presentation sizeof="screen" gridspacingx="49152"
gridspacingy="49152">
<p:master id="8" slidesn="1C00DA9,3702FA30"
type="main" href="master08.htm"
xmlhref="master08.xml" template="Pixel"
layout="title_body"
slots="title,body,dateTime,footer,slideNumber">
<p:schemes>

Why XML and not HTML?
n Unlimited tagsets and definitions
¨XML is a metalanguage
n HTML describes a web page
¨XML describes all manner of “documents”
n That is, HTML is fixed, limited and informal
¨XML is versatile, multifaceted and formal

Advantages of XML
n Rigorous Grammar – all tags are balanced
n Open Standard – anyone can use XML
n Flexibility – can define many types of data
n Relatively Simple – concepts are easy

XML has a Rigorous Grammar
n Balanced Tags
n Tags come in sets
This is some bold text
<ol><li>One Item</li>
<li>Second Item</li></ol>
n Individual tags must have a terminator
 
n Tags must be nested – cannot overlap
Invalid

XML has a Rigorous Grammar
n DTD – Document Type Definition
¨ DTD defines how the document is structured, that is, allowable tags and
grammar
¨ Sets rules for the document, such as:
A is part of a <chapter> which is part of a <book> -- but don’t allow a 
in a <toc>
n Schemas – A Restriction of DTD
¨ Can use multiple schemas with a given DTD
n Rigorous Grammar = Machine Readable
¨ Platform independent…software independent
¨ If you know the DTD, you can write software to read that type of XML
file.
¨ Correctly formatted XML can be parsed.

XML is an Open Standard
n W3C has control of the XML specification
¨World Wide Web Consortium-Cambridge, MA
¨http://www.w3.org/XML/Core/#Publications
n Anyone can use the standard – no fees
n Only the W3C can maintain and update
n W3C maintains many web standards…
…such as: HTML, XHTML, CSS, PNG

XML is Flexible
n No predefined tags…
n …DTD defines the grammar…
n …which means that XML can contain
n Text, Graphics, Video … and so on.
n Many new languages appearing that are
based on XML.
¨Such as….

Flexibility – XML-based Languages
n XHTML:Extensible HyperText Markup Language
n MetaL: Meta Programming Language
n MML: Music Markup Language
n XBRL: Extensible Business Reporting Language
n MathML: Mathematical Markup Language
n OML: Weather Observation Definition Format
n Adex: Newspaper Classified Ads Format
n AML: Astronomical Markup Language
n rezML: Resume and Job Listing Markup Lang.

XML as a concept is simple
n Designed as a common platform for
electronic delivery of data
n The Swiss Army Knife of file formats
n Simpler than SGML
¨XML is actually a simplified subset of SGML
¨Standard Generalized Markup Language
¨SGML & XML were both initially intended to
facilitate large-scale electronic publishing

Why XML and not SGML?
n Simpler structure
¨ Easier to parse… and therefore…
¨ …easier to build software
¨ SGML systems are complex & expensive
¨ XML-based systems are much easier to build
n …easier to transmit on the Internet.
n Greater degree of flexibility…
…with less complicated grammar.

Can I parse it and does it validate?
n Properly formatted documents can be
mechanically validated for correctness
n Validation ensures proper structure…
…does not ensure correct content
n All XML-based languages can be validated
n XHTML @ http://validator.w3.org/

XML and XSL/XSLT
n Extensible Stylesheet Language
n Like Cascading StyleSheets in HTML
n Defines the look of an XML document
n …that is, how individual tags are
presented in, say, a browser or software
n Multiple stylesheets for multiple uses
(i.e. print, on-screen, etc.)

RSS: Really Simple
Syndication
A New Way to Read and
Receive News on the Internet

The RSS Format
n Really Simple Syndication … or,
n RDF Site Summary
n A way to provide headlines and content through
a method of syndication
n Exciting new format being used…
n …by the press and by individuals (e.g. blogs)
n You can “subscribe” to an RSS news feed.

RSS Readers
n A program designed to read RSS feeds.
n SharpReader, Syndirella, Radio Userland
n Common: 3-pane window (like email)
n Also: some use a web-based reader
n The reader automatically updates the
feeds on a regular basis.
n Full text messages vs. Summaries

RSS is another example of XML
n RSS is an XML-based language
n Profusion of versions and formats
¨7 different versions
¨And 2 significantly different formats
¨A problem with non-proprietary standards
n RDF – Resource Description Framework

XML in Libraries
What does XML mean to the
modern library?

XML in Libraries
n Uses:
¨Digital Collections / Digital Libraries
¨Metadata & Cataloging
¨Document delivery
¨Archival storage

XML & Digital Collections/Libraries
n Storage format for digital objects
n Encoded Archival Description (EAD)
– uses SGML – shift to XML
http://www.loc.gov/ead/
n XML: the new standard
n Interoperability – less likely obsolescence

XML & Metadata/Cataloging
n Metadata Encoding and Description Standard (METS)
http://www.loc.gov/standards/mets/
n Dublin Core XML Schemas
http://www.dublincore.org/schemas/xmls/
n Open Archives Initiative Protocol for Metadata
Harvesting (OAI-PMH)
-- a schema for MARC records in XML
http://www.openarchives.org/OAI/2.0/guidelines-
oai_marc.htm
n RDF – Dublin Core, Open Directory and General
Purpose Catalogs
http://www.w3.org/RDF/#gen-col

XML & Archival Storage
n TEI: Text Encoding Initiative
using an SGML encoding scheme that is maximally
expressive and minimally obsolescent
http://www.tei-c.org/
n HPSS: High Performance Storage System
http://www.sdsc.edu/hpss/
n ADSM
n The Question: Is XML an Archival Format?

HYPERLINKS to RESOURCES
n http://www.w3.org/XML/
n http://www.xml.com/
n http://www.xml.com/pub/a/98/10/guide0.html
n http://www.tei-c.org/
n http://www.dublincore.org/schemas/xmls/
n http://validator.w3.org/
n http://www.ucc.ie:8080/cocoon/xmlfaq

That’s all folks!
nQuestions?
n Find this presentation at:
http://staffweb.lib.uiowa.edu/dstout/xml.htm

XML Standard for Data Encapsulation

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