Microformats

Outline (Microformats)

Microformats [7]
Resource Description Framework (RDF) [5]
More Languages [2]

Microformats E. Wilde: Web Semantics in Practice

(5) HTML Microformats

<html lang="en-US" xml:lang="en-US" xmlns="http://www.w3.org/1999/xhtml">
 <head>
  <title>Erik Wilde</title>
  <link rel="next" href="cv" title="CV"/>
  <link rel="prev" href="publications" title="Publications"/>
  <link rel="glossary" href="http://dret.net/glossary/"/>
  <link rel="stylesheet" type="text/css" href="http://dret.net/dretnet.css"/>
  <link rel="stylesheet" type="text/css" href="http://dret.net/netdret/netdret.css"/>
  <link rel="meta" type="application/rdf+xml" title="FOAF" href="http://dret.net/netdret/foaf.rdf"/>
  <link rel="icon" href="http://dret.net/favicon.ico" type="image/x-icon"/>
  <link rel="shortcut icon" href="http://dret.net/favicon.ico" type="image/x-icon"/>

dret.html (line 2-12)

HTML has some built-in microformats
- support for attaching semantics to links
- structured documents can be made explicit on the Web

Microformats E. Wilde: Web Semantics in Practice

(6) vCard Microformat (hCard)

  <div class="vcard">

dret.html (line 16)

       <span class="fn">Erik Wilde</span>

dret.html (line 24)

      <i class="email"><a href="mailto:dret@berkeley.edu" title="Send email to dret@berkeley.edu">dret@berkeley.edu</a></i>

dret.html (line 34)

      <i class="tel"><a href="tel:+1-510-2061079" title="Call +1-510-2061079" id="mobile">+1-510-2061079</a></i> /

dret.html (line 42)

      <i class="tel"><a href="tel:+1-510-6432253" title="Call +1-510-6432253" id="tel">+1-510-6432253</a></i> /

dret.html (line 51)

Microformats E. Wilde: Web Semantics in Practice

(7) Location Microformats

  <p><em>Geolocation</em> (GPS coordinates), for example
   <span class="geo">Grizzly Peak:
    <span class="latitude">37.882045</span>,
    <span class="longitude">-122.233698</span>
   </span>
  </p>
  <hr />
  <p><em>Address information</em> (requires geocoding), for example
   <span class="adr">School of Information:
    <span class="extended-address">311 South Hall</span>,
    <span class="street-address">South Hall Road</span>,
    <span class="region">Berkeley</span>
    <span class="region">CA</span>
    <span class="postal-code">94720-4600</span>,
    <span class="country-name">USA</span>
   </span>
  </p>

location-microformats.html (line 9-25)

Microformats E. Wilde: Web Semantics in Practice

(8) Islands of Semantics

Microformats solve very specific problems in a very specific way
- encoding address information on a Web page
- encoding a location of something represented by a Web resource
Microformats can be compared to tagging
- a very simple mechanism with a minimal barrier-to-entry
- little flexibility in adapting the mechanism to slightly other uses
- often underspecified and interpretation implementation-dependent
- no unified rules across different platforms which makes processing hard
- nice and easy to start with, but questionable for robust long-term solutions
Currently there are about 10 reasonably popular microformats
- calendar entries, addresses, licenses, outlines, geolocation, resumes, social networking, … [http://microformats.org/wiki/Main_Page]

Microformats E. Wilde: Web Semantics in Practice

(9) Microformat Syntax

HTML has some underspecified and underused elements
- dfn, code, samp, kbd, var, cite, abbr, acronym
- they can be reused and augmented with additional information
HTML allows non-HTML content in HTML pages
- unknown elements and attributes must be ignored
HTML allows class attributes to carry semantics
HTML has a head which contains page metadata
- for example, the link element specifies connections to other resources

Microformats E. Wilde: Web Semantics in Practice

(10) Magic Names

A syntax defines where and how to embed information
- what is embedded and how well is it defined semantically?
- is there an underlying model for specifying dependencies?
- how many assumptions does it take to implement a microformat?
Names are never self-explanatory, they always represent concepts
- nothing can remove the burden of defining a conceptual model
- if this is not done, models evolve and there will be more than one
Microformats and tagging share the same folklore
- define simple things and good things will happen
- this works by supporting a quickly growing ecosystem of diverging semantics
- semantics are most useful when they are well-defined
- loose semantics also have some utility

Microformats E. Wilde: Web Semantics in Practice

(11) Microformats on the Web

Easy to embed for generated content
- some of the very basic formats may even appear in browsers one day
- combining well-designed URIs with document relationships is better than every site map
Hard to rely on for applications that need dependable semantics
- useful as a hint and as a starting point
- microformats are not a good idea for complex information management tasks
Use as foundation for representing common concepts
- when formatting addresses, use adr [http://microformats.org/wiki/adr] class names
- for structured documents use XOXO [http://microformats.org/wiki/xoxo]

Resource Description Framework (RDF)

Outline (Resource Description Framework (RDF))

Microformats [7]
Resource Description Framework (RDF) [5]
More Languages [2]

Resource Description Framework (RDF) E. Wilde: Web Semantics in Practice

(13) Describing Resources

RDF describes everything in triples
- making a statement about a resource (identified by a URI [Web Foundations (URI & HTTP); Uniform Resource Identifier (URI) (1)])
- describing a certain property of the resource
- specifying a value for that property

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#">
  <contact:Person rdf:about="http://www.w3.org/People/EM/contact#me">
    <contact:fullName>Eric Miller</contact:fullName>
    <contact:mailbox rdf:resource="mailto:em@w3.org"/>
    <contact:personalTitle>Dr.</contact:personalTitle> 
  </contact:Person>
</rdf:RDF>

[http://www.w3.org/TR/REC-rdf-syntax/#intro]

Resource Description Framework (RDF) E. Wilde: Web Semantics in Practice

(14) RDF Graphs

Resource Description Framework (RDF) E. Wilde: Web Semantics in Practice

(15) RDF is Simple and Complex

RDF's abstract model [http://www.w3.org/TR/rdf-concepts/] is the idea of descriptive triples
- the actual RDF model is rooted in description logic
- RDF itself can only describe individuals (something identified by URI)
RDF/XML [http://www.w3.org/TR/rdf-syntax-grammar/] is an XML syntax for encoding triples
- the syntax allows a variety of ways to represent the same RDF statements
- processing RDF/XML with XML tools is likely to fail
- use RDF parsers to parse all variations of RDF/XML into an abstract RDF graph
RDF Schema [http://www.w3.org/TR/rdf-schema/] supports the creation of RDF vocabularies
- describe the classes of things that can be used in statements
- describe the properties which can be used for each of these classes
- describe the allowed values for the supported properties

Resource Description Framework (RDF) E. Wilde: Web Semantics in Practice

(16) RDF Schema Graph

Resource Description Framework (RDF) E. Wilde: Web Semantics in Practice

(17) RDF in Attributes (RDFa)

Microformats can use any kind of markup design
- this makes it hard to detect microformats when processing a Web page
- combining microformats can become complicated and ill-designed
RDFa defines only a syntax for embedding metadata into XHTML
- the vocabulary must be described by some RDF schema language

<p>This document is licensed under a <a xmlns:cc="http://creativecommons.org/licenses/" rel="cc:license" href="http://creativecommons.org/licenses/by/nc-nd/3.0/">Creative Commons License</a>.</p>

RDFa uses and extends HTML for embedding RDF
- it uses HTML's rel, rev, href, and src attributes
- it defines a number of new attributes for HTML elements [http://www.w3.org/TR/rdfa-syntax/#s_metaAttributes]
- it defines a processing model [http://www.w3.org/TR/rdfa-syntax/#s_model] for deriving RDF triples from these attributes

More Languages

Outline (More Languages)

Microformats [7]
Resource Description Framework (RDF) [5]
More Languages [2]

More Languages E. Wilde: Web Semantics in Practice

(19) SPARQL

RDF graphs can be large and hard to handle
- querying RDF graphs using XML technologies is hard and slow
- special data structures need special query languages
- SPARQL is a query language for querying RDF graphs
Using RDF without using SPARQL does not make a lot of sense
- if the data is simple and restricted, why use RDF?
- processing unrestricted RDF without a special language is very hard
Semantic Web search engines can harvest the Web for RDF
- the result is a huge graph of RDF describing all semantic Web resources
- querying into this graph retrieves all formalized semantics on the Web

More Languages E. Wilde: Web Semantics in Practice

(20) Web Ontology Language (OWL)

RDF and RDF Schema are rather basic languages
OWL adds more sophisticated features to RDF Schema
- constructions of classes using existing ones
- characterize relationships (e.g., whether they are transitive, symmetric, functional, etc.)
Formal semantics are hard to write and compute
- no property expressions or datatypes in RDF Schemas
- not all set operators, restricted cardinality in OWL Lite
- some restrictions, but a computational guarantee in OWL DL
- full expressive power in OWL Full (but no computational guarantee)

Web Semantics in Practice

Web Architecture and Information Management [./]
Spring 2009 — INFO 190-02 (CCN 42509)

Erik WildeUC Berkeley School of Information, UC Berkeley School of Information
2009-04-29

Contents

(2) Abstract

(3) Using Semantics

Microformats

Outline (Microformats)

(5) HTML Microformats

(6) vCard Microformat (hCard)

(7) Location Microformats

(8) Islands of Semantics

(9) Microformat Syntax

(10) Magic Names

(11) Microformats on the Web

Resource Description Framework (RDF)

Outline (Resource Description Framework (RDF))

(13) Describing Resources

(14) RDF Graphs

(15) RDF is Simple and Complex

(16) RDF Schema Graph

(17) RDF in Attributes (RDFa)

More Languages

Outline (More Languages)

(19) SPARQL

(20) Web Ontology Language (OWL)

(21) Semantics are Important and Hard

Web Semantics in Practice

Web Architecture and Information Management [./]Spring 2009 — INFO 190-02 (CCN 42509)

Erik WildeUC Berkeley School of Information, UC Berkeley School of Information2009-04-29

Contents

(2) Abstract

(3) Using Semantics

Microformats

Outline (Microformats)

(5) HTML Microformats

(6) vCard Microformat (hCard)

(7) Location Microformats

(8) Islands of Semantics

(9) Microformat Syntax

(10) Magic Names

(11) Microformats on the Web

Resource Description Framework (RDF)

Outline (Resource Description Framework (RDF))

(13) Describing Resources

(14) RDF Graphs

(15) RDF is Simple and Complex

(16) RDF Schema Graph

(17) RDF in Attributes (RDFa)

More Languages

Outline (More Languages)

(19) SPARQL

(20) Web Ontology Language (OWL)

(21) Semantics are Important and Hard

Web Architecture and Information Management [./]
Spring 2009 — INFO 190-02 (CCN 42509)

Erik WildeUC Berkeley School of Information, UC Berkeley School of Information
2009-04-29