Post on 22-Dec-2015
transcript
H. Weinberger - A. Frank2
Contents of Metadata Lecture
1. Introduction to Metadata2. Interoperability of Metadata3. Evolution of Descriptive Metadata4. Web Descriptive Metadata5. Structured Metadata6. Semantic Web
H. Weinberger - A. Frank3
Content
1. Introduction 2. Context and Meaning3. Web sites requirements:
challenges and possible solutions
4. Web document standards HTML and XML Understanding XML Understanding RDF
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1 .Introduction
מידע-על מבניStructured metadata הוא מידע-על מובנה )פורמלי( מובן למכונה )מחשב(
מונחים נרדפים בשימוש: שפות סימון, שפות תחביר מתארות מבנה סימוןשפות (Structure) פורמט וFormat) )
בהם מוצג הטקסט..מידע-על מבני בדרך כלל נפרד מהתכנים שיטות ההבניה הנפוצות ביותר בשימוש הן ממשפחתSGML
:שהיא.(Markup specification)מערכת כללים לתיאור תחביר – SGMLמפרט מסוים שמוגדר באמצעות –
Document Type Definition .)DTD(
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3. Web Sites Requirements
Standardize on logical views, not physical implementations.
Standard description of logical views available:– More than databases actually did.
Sites can interact with each other and with clients!
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3.1 Challenges to Realize the Web’s Full Potential...
Find information intelligently.Interact with applications on
servers easily and efficiently.But: physical implementations
will vary from site to site.
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3.2 Information retrieval and descriptive metadata
The need: exchange metadata from different schema.
The solution:– RDF: framework for syntax and structure – XML: representation language– DC: metadata schema
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4.Web Document Standards
SGML - Standard Generalized Markup Language HTML - Hypertext Markup Language XML - Extensible Markup Language RDF - Resource Description Framework
SGML XML- structure
SGML app
HTML XML app
RDF- semantics
RDF app.
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HTML
Began as a simple markup language for Web documents . Brought into closer compliance with SGML )HTML 2.0
includes an SGML DTD(. A DTD states what tags and attributes are used to describe
content in an SGML document, where each tag is allowed, and which tags can appear within other tags.
Common usage still flaunts SGML conventions.
HTML Structural elements:
גוף המסמך, פסקאות, כותרות, שורה חדשה, טבלה, רשימה– Document appearance
גופן, מירכוז וכיוצ"ב–
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XML – What is it?
Extensible Markup LanguageAn XML document primarily consists of nested
hierarchy of elements with a single root. Elements can contain character data, child elements, or a mixture of both – and they can have Attributes.
An XML markup language is defined in a DTD )Document Type Definition(.
http://www.cs.ucl.ac.uk/staff/A.Finkelstein/syllabusresources.html
XML DTD declares:– Elements– Attributes
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What is XML – what does it do
XML tags don’t describe user interface. There is no default presentation for each tag. They describe information.– XML has no special tags for titles or lists or
paragraphs or images. – It isn’t a presentation grammar. It is a way to
encode any information.
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What is unique in XML vs. HTML
Tags may not overlap each other.Example of illegal XML:
– <Person><Name>Adam</Name><KeyPoint><Heading>XML provides a data bus</Heading> </Person><More>…</More> </KeyPoint>
Example of legal XML:– <Person>
<Name>Adam Bosworth</Name> <Title>General Manager</Title> <Age>42</Age></Person>
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XML's suitability as a universal data format for the Web
Open standards and extensibility Separation of content, presentation,
linkingComputer platform and software
application neutrality, interoperabilityUnicode and data longevity Will XML DTDs or schemas replace
MARC?
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XML- Towards Semantic Web
XML: towards meta-grammer for inter-organizational communication around the Web.
XML schema is an emerging standard from W3C. XML schema is a language for defining the structure of XML document instances that belong to a specific document type.
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XML DTDs Possibilities
Provide a formal and complete definition of an XML vocabulary.
Are sharable descriptions of a the structure of an XML document.
Are a way to validate specific instances of XML documents and constrain their content.
Are restricted to on DTD per document instance.
מערכתאפשר להגדיר DTD’s.של
מגדיר אלמנטיםבכל שסביר שצריך
.המסמכים ,לכאורהHTML הוא
שמערב DTDסוג של יסודות מבניים עם
.צורניים
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Resource Description Framework (RDF)
שיטה באמצעותה ניתן לבצע חילופין של מידע-על: .: מודל מבני לביטוי תחבירכן–.: ציון סמנטיקה של מידע-עללא–
על, דוגמת -בסכמת מידעDC שלושה היבטים, קיימים:Semantic ההיבט הסמנטי מתאר כיצד להבין מושגים כמו :
Data, CreatorDC, לדוגמא, לציין שהכוונה במובן creatorכיצד להבין מושגים כמו
Syntax ההיבט התחבירי מפרט כיצד לבטא את המידע-על :. creatorלדוגמא: תאור המחבר ייעשה באמצעות האלמנט
Structureמבנה מגדיר יחסים בין אלמנטים של מידע-על : לדוגמא: יום, תאריך ושנה
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RDF Objects
:משפט בשפה טבעית המלט )המחזה( של )סוג התייחסות( הוא המחבר )ערך( שייקספיר
)משאב מתואר(
Resources: Things described )Hamlet( Properties: Specific aspects )attributes,
relations( used to describe a resource )…Author(
Statements: A specific resource + a named property + the value of that property for that resource )…Shakespeare(
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RDF Structural Model
Resource Property type Value Hamlet creator Shakespeare
A different metadata scheme might use author in place of creator, and ,might use type for a different meaning, therefore, the RDF markup make explicit that this metadata is expressed in the DC schema, as follows:
<DC:creator>Shakespeare</DC:creator><DC:type>play</DC:type>A more precise Hamlet description, using imaginary URL:
<RDF:RDF><RDF:description RDF:about=http://hamlet.org/>
<DC:creator>Shakespeare</DC:creator><DC:type>play</DC:type>
<RDF:description><RDF:RDF>
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RDF Application Capabilities
in resource discovery to provide better search engine capabilities.
in cataloging for describing the content and content relationships.
by intelligent software agents to facilitate knowledge sharing and exchange.
in content rating in describing collections of pages that represent a single logical "document“.
for describing intellectual property rights of Web pages.
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Web Metadata & Web Future
Searching on the web will become easier as search engines have more information available. Searching can be more focused. Doors will also be opened for automated software agents to roam the web.
The web of today, the vast unstructured mass of information, may in the future be transformed into something more manageable - and thus something far more useful.
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References
XML Adam Bosworth, XML:A Revolution Unfolds Cover, robin, Extensible Markup Language )XML( http://www.oasis-open.org/cover/xml.html W3C Extensible Markup Language )XML( 1.0 http://
www.xml.com/axml/axml.html Ronald Bourret, Declaring Elements and Attributes in an XML
DTD http://www.rpbourret.com/xml/xmldtd.htm XML DTD Example
http://www.cs.ucl.ac.uk/staff/A.Finkelstein/syllabusresources.html
RDF Site Summary )RSS(
http://groups.yahoo.com/group/rss-dev/files/specification.html
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Contents of Metadata Lecture
1. Introduction to Metadata2. Interoperability of Metadata3. Evolution of Descriptive Metadata4. Web Descriptive Metadata5. Structured Metadata6. Semantic Web
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What is the Semantic Web? (1)
"The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation."
Tim Berners-Lee, James Hendler, Ora Lassila, Consistent logical web of data = Semantic
Web
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What is the Semantic Web? (2)
“The Web is about links; the Semantic Web is about the relationships implicit in those links.” Dan Brickley
Semantic Web is part of the W3C technology and society domain. – Manage the development of enabling standards
and technologies. The Semantic Web is a web whose content
can be processed by computers. … an infrastructure for supplying the Web with formalized knowledge…” Jerome Euzenet, EU-NSF 2002
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Research Organizations
W3CEuropean Union Future Emergent
Technology program )EU-FET(National Science Foundation )NSF(
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Metadata & the Semantic Web
Meta-data is the fundamental building block of the Semantic Web. Mikael Nilsson et al.
Metadata architecture - envisioned as an "ecosystem" of ever-evolving interpretations layered upon objects as they are created, used and reused. Scott Wilson, CETIS staff )centre for educational technology interoperability standards(
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The Current Web in Context
Web is a set of Resources and Links Resources identified by URI's Uniform Resource Identifiers.
To a user, this has become an exciting world To a machine, however, very little machine-readable information is avaliable.
The meaning of the documents is clear to those with a grasp of )normally( English. The significance of the links is only evident from the context around the anchor.