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Panos Alexopoulos
Data and Knowledge Technologies
Professional
http://www.panosalexopoulos.com
p.alexopoulos@gmail.com
@PAlexop
From Taxonomies and Schemas to Knowledge Graphs
Recognizing and tackling the pitfalls of
large-scale semantic modeling
In 2016 I got a mission
“Good morning Mr.
Alexopoulos. Your mission,
should you decide to accept it
is to build a Knowledge Graph
for the Labour Market Domain.”
—Textkernel
which I accepted as I had the perfect recipe
that often didn’t quite work as expected
leading to an important lesson
Semantics are
pretty hard to
scale!
Workshop
Identity
Knowledge Graphs
Semantics
Scale
Pitfalls
Knowledge
Graphs &
Semantics
Understanding the interplay
Knowledge Graphs are
interconnected entities
under shared semantics
Not something really new but rather a
rebranding of terms like semantic
networks, knowledge bases, ontologies,
linked data
If you have been designing database
schemas, taxonomies, ontologies or other
types of structured data, you already know
a lot about knowledge graphs.
What you may have missed is the shared
semantics aspect!
RDF, Property Graphs, JSON-LD,
NoSQL, ...
Small, medium, large, densely
connected, sparsely connected,
...
Concrete entities, abstract
entities, “real-world” entities,
hierarchical relations, entity
attributes, relation attributes,
associative relations,
constraints, axioms, rules, ...
Single domain, multiple
domains, single context,
multiple context
Data Analytics, Data Integration,
Semantic search, Question
answering, Reasoning
Important (but non-defining)
dimensions of Knowledge Graphs
TECHNOLOGY STACK SIZE AND CONNECTIVITY
EXACT NATURE OF
ELEMENTS
SCOPE PURPOSE
Crucial dimensions of Knowledge
Graphs
MEANING
ACCURACY
How correct/accurate
is the meaning of each
entity, relation or other
element for all people
and systems that use
the graph.
MEANING
EXPLICITNESS
How clear and
unambiguous is the
meaning of each entity,
relation or other
element for all people
and systems that use
the graph.
MEANING
AGREEMENT
How commonly
acceptable is the
meaning of each entity,
relation or other
element among the
people and systems
that use the graph.
“Enemies” of accuracy, explicitness
and agreement
AMBIGUITY VAGUENESS
BAD MODELING
DIVERSITY/VARIETY SEMANTIC CHANGE
Semantics
CSI
Investigating bad semantic modeling
practices
The “Crime” Scenes
SNOMED: A systematically organized
computer processable collection of
medical terms providing codes, terms,
synonyms and definitions used in
clinical documentation and reporting
KBPedia: A comprehensive knowledge
structure combining seven 'core' public
knowledge bases — Wikipedia, Wikidata,
schema.org, DBpedia, GeoNames,
OpenCyc, and UMBEL — into an
integrated whole
The “Crime” Scenes
Schema.org: A collaborative,
community activity with a mission to
create, maintain, and promote
schemas for structured data on the
Internet, on web pages, in email
messages, and beyond.
DBPedia: A large knowledge graph
automatically extracted from
Wikipedia infoboxes
The “Crime” Scenes
ESCO: A knowledge graph about
occupations, skills and
qualifications for the European
Labour Market, built by the European
Commision

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From Taxonomies and Schemas to Knowledge Graphs: Parts 1 & 2

  • 1. Panos Alexopoulos Data and Knowledge Technologies Professional http://www.panosalexopoulos.com p.alexopoulos@gmail.com @PAlexop From Taxonomies and Schemas to Knowledge Graphs Recognizing and tackling the pitfalls of large-scale semantic modeling
  • 2.
  • 3. In 2016 I got a mission “Good morning Mr. Alexopoulos. Your mission, should you decide to accept it is to build a Knowledge Graph for the Labour Market Domain.” —Textkernel
  • 4. which I accepted as I had the perfect recipe
  • 5. that often didn’t quite work as expected
  • 6. leading to an important lesson
  • 11. Scale
  • 13.
  • 15. Knowledge Graphs are interconnected entities under shared semantics Not something really new but rather a rebranding of terms like semantic networks, knowledge bases, ontologies, linked data If you have been designing database schemas, taxonomies, ontologies or other types of structured data, you already know a lot about knowledge graphs. What you may have missed is the shared semantics aspect!
  • 16. RDF, Property Graphs, JSON-LD, NoSQL, ... Small, medium, large, densely connected, sparsely connected, ... Concrete entities, abstract entities, “real-world” entities, hierarchical relations, entity attributes, relation attributes, associative relations, constraints, axioms, rules, ... Single domain, multiple domains, single context, multiple context Data Analytics, Data Integration, Semantic search, Question answering, Reasoning Important (but non-defining) dimensions of Knowledge Graphs TECHNOLOGY STACK SIZE AND CONNECTIVITY EXACT NATURE OF ELEMENTS SCOPE PURPOSE
  • 17. Crucial dimensions of Knowledge Graphs MEANING ACCURACY How correct/accurate is the meaning of each entity, relation or other element for all people and systems that use the graph. MEANING EXPLICITNESS How clear and unambiguous is the meaning of each entity, relation or other element for all people and systems that use the graph. MEANING AGREEMENT How commonly acceptable is the meaning of each entity, relation or other element among the people and systems that use the graph.
  • 18. “Enemies” of accuracy, explicitness and agreement AMBIGUITY VAGUENESS BAD MODELING DIVERSITY/VARIETY SEMANTIC CHANGE
  • 20. The “Crime” Scenes SNOMED: A systematically organized computer processable collection of medical terms providing codes, terms, synonyms and definitions used in clinical documentation and reporting KBPedia: A comprehensive knowledge structure combining seven 'core' public knowledge bases — Wikipedia, Wikidata, schema.org, DBpedia, GeoNames, OpenCyc, and UMBEL — into an integrated whole
  • 21. The “Crime” Scenes Schema.org: A collaborative, community activity with a mission to create, maintain, and promote schemas for structured data on the Internet, on web pages, in email messages, and beyond. DBPedia: A large knowledge graph automatically extracted from Wikipedia infoboxes
  • 22. The “Crime” Scenes ESCO: A knowledge graph about occupations, skills and qualifications for the European Labour Market, built by the European Commision