HTML and CSS Reference
In-Depth Information
Chapter 7
Metadata and the Semantic Web
The basic structure of web documents provides the desired appearance and functionality. By default, however, the
content is human-readable only. You can use additional technologies to provide meaning to web documents, making
them machine-readable and human-readable at the same time. There is a wide choice of metadata available, along
with microformats and various annotations that can significantly extend the processability of web documents and the
efficiency of web searches. Structured data should be added to web sites and conventional search engines changed
from brute-force approaches to semantic parsing.
In this chapter, you will learn machine-readable metadata annotations and semantically meaningful attributes.
You will also become familiar with the Resource Description Framework, the fundamental standard behind Semantic
Web technologies. After reading the chapter, you will be able to create new vocabularies, schemes, and ontologies,
and use existing technologies such as
General metadata in the markup : Conventional meta tags
Microformats : Metadata provided as attribute values of markup elements
Microdata : A metadata annotation for general metadata embedding in HTML5
RDF : A standardized framework for Semantic Web data models
OWL : A knowledge representation language for describing and sharing web ontologies that
formally represent knowledge as a set of concepts within a domain and the relationships
between those concepts
FOAF and DOAC : Machine-readable ontologies for people and their professional capabilities
XMP, Rich Snippets, SearchMonkey RDFa : Metadata formats for images and video clips
The Semantic Web
Until recently, software agents could not handle many kinds of information that could have been associated with
files. Although file structure and extensions provided some information about files, much information could not be
expressed. For example, a file with a .jpg extension has always represented a JPEG image but provided no information
about the shutter speed, exposure program, f-stop, aperture, ISO speed rating, or focal length until the introduction
of metadata formats such as Exif and XMP (see Chapter 9). However, sharing metadata stored in binary files is still
not the most efficient way to share metadata, especially if it is much more generic. In the digital era, electronic files
are being sold (e-books, MP3 files, and so on) that might be retrieved or played on many types of devices. A variety of
metadata technologies can be used to express arbitrary information and represent any kind of knowledge associated
with electronic documents in a machine-readable format. Machine-readable data (automated data) is data stored in
a machine-readable format, making it possible for automated software agents to access and process it without human
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