Semantic Web Technologies
• Brief Readings Discussion
• Class work: Research topics and Project
discussion
• Research Presentations
How do we organize information?
• Emulate real-world structures?
• Invent abstract structures?
• We can’t help seeing patterns & classifying
• What does your organizational structure say
about you?
- Culture
- Philosophy
- Profession
• What does the Semantic Web do for
organization?
What is a Taxonomy?
• What are some examples of a taxonomy?
• “a way of classifying or categorizing a set of
things”…
• “a classification in the form of a hierarchy”
• What do we mean by hierarchy?
- A “tree-like structure” with a root & branches (nodes)
• A hierarchic organization scheme based on the
properties & relationships of the elements in the set
- Sub & super classes
- Parent & child nodes
• Taxonomies provide some kinds of semantic meaning
Semantic Relationships
• Hierarchies can express meaning
• Levels of the hierarchy imply strength of meaning (or
relation)
• Distinct, distinguishing properties that help you
identify (& organize)
- More specific properties as you go down the hierarchy
- Relationships & similarity help define the lower levels
• Taxonomies are models of information (& elements)
• Taxonomies should represent the semantic
relationships among elements
Why do we use taxonomies?
• To organize things (elements)
• To make sense of the world
- But what if you don’t know much about the world?
- (Mapping problems)
• To get agreement on our view of the world
- To persuade others about our view of the world?
• To make things easier to (re)find
- For whom?
Topic Maps
• “A set of linked topics” p167
• An instantiation of a taxonomy
- A semantic web-enabled taxonomy?
• Overlays for content
- Anything can be a topic
- Too many things may be a topic?
• Multiple views of information
• An Information Architecture of sorts
- We’ll talk more about Topic Maps later
The Ontology Spectrum
Unpacking the Ontology Spectrum
• Semantic richness increases as you go up &
to the right
• Taxonomy
- Knowledge with minimal hierarchy)
• Thesaurus
- Language (words & synonyms) (see Table 7.4)
• Conceptual Model
- Logical theory (for one)
• Local Domain Theory / Logical Theory
- Classification with specifics (that machines can
use)
So what’s an ontology?
• “An ontology defines the common words and
concepts (meanings) used to describe & represent an
area of knowledge, and so standardizes the
meanings.” p166
- They encode knowledge in (& across) a domain
- They make
- They make knowledge reusable
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Classes (general things) (varied domains)
Instances (particular things)
Relationships
Properties (& values)
Functions (& processes)
Constraints (& rules)
Let’s keep ontologies simple
• “vocabularies and their meanings, with explicit,
expressive, and well-defined semantics”
• Describe an area of knowledge
- Vocabularies & their concepts
• Are ontologies combinations of taxonomies?
- Taxonomies=2D, Ontologies=3D?
• Define the semantics of a domain
• Tools for learning & understanding a concept
• Classes, relationships & attributes
• What’s the underlying philosophy represented here?
- A view of some part of the world?
Ontologies Capture Meaning
• And this meaning can be called Semantics
• The Semantic Web relies on Ontologies to
make logical decisions & to perform actions
• You can use any manner of ways to build an
ontology
- Any number of possible ontologies too
• Different types of logic define & shape
ontologies
- Depending on the use
- Depending on the tool
- Depending on the builders (“little o”)
Ontologies & Representation
• The semantic web needs ontologies with
specific representation
• “representing means that we encode the
description in a way that enables someone to
use the description.” p`87
• The terms (thesaurus, vocabulary) are
combined to be specific
- Are more terms always more specific?
- In a taxonomy, the lower the level, the larger the
numbers of terms?
Parts of an Ontology
• The Logic of an Ontology is represented by:
• Syntax
- Form, format & structure
- Markup (it’s own logic & order)
• Structure
- Built from syntax
- Taxonomy-driven, but also graphs
• Semantics
- Mapping meaning to intended use(s)
- Making the ontology machine-understandable (actionable)
• Pragmatics
- New (& last) in most Semantic Web efforts
- Subtleties that help programs run logic (ordered)
Using Taxonomies & Ontologies
• For the Semantic Web…
• Semantic meaning can be represented & used
• You can use (& re-use) information structures that
describe & house information for actionable use
• Markup formats (many of them) can be used to
formally describe information as you want it used by
others
• Sharing, updating & modifying structures can be
tracked & implemented
• Others can extend your work, you can extend theirs