every identity, its ontology
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Every Identity,
Its Ontology
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Every Identity,its Ontology
Robert SandersonSemantic ArchitectJ. Paul Getty Trust
[email protected] / @azaroth42
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Every Identity,
Its Ontology
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The shared identity of the concept of the fictional person
Dr Strangelove: How I learned to stop worrying
and love inconsistency
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Every Identity,
Its Ontology
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Overview
• Linked Open Data and Identity• Philosophical Challenges• Practical Challenges• Practical Philosophy• A Philosophy of Practicality
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Linked Open Data’s PotentialLinked Open Data achieves its potential when institutions: • link outside of their own data (⭐⭐⭐⭐⭐),• trust other organizations tomanage, publish and maintain data which they use
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Linked Open Data’s ChallengesCommonly cited:• Amount of data to transform• Data is mostly “strings”, not “things”• Cost of new management system• Cost of new business workflows• Difficulty of data enrichment• Institutional reluctance to embrace change,
trust, imperfection
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Every Identity,
Its Ontology
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Identity
We need to understand the entity before we can reuse its identifier!
Questions:1. What constitutes “identity”?2. How does one describe entities?3. How does one discover identifiers?
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Every Identity,
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LOD Identity Fundamentals
• Open World Assumption• What is not stated is unknown, not false• No single agent or observer has complete knowledge in a distributed system
• Identifier space is infinite• No formal character limit for IRIs• Even practical limit is very large (65536 ^ length)
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Every Identity,
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LOD Identity Fundamentals
• IRIs are globally unique• IRIs used for identifying entities and relationships• No identity for instance of a relationship• Only one contextual identity (named graph)per statement, with inconsistent use• Anyone may make assertions about any entity
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Every Identity,
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Every Identity, …
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Every Identity,
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http://www.getty.edu/art/collection/objects/249050/
… some Philosophy• RDF falls in Plato’s “Universals” space• Same relationship had by many entities• No relationship instances• Fictional entities and relationships ok
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Every Identity,
Its Ontology
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1. Indiscernibility of Identicals
for each object a:
for each object b:
if a === b:
for each property P:
P(a) === P(b)
Or … owl:sameAs
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Every Identity,
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Open World Ramifications
If we know that a owl:sameAs b
And discover that a property x
Then we know that b property x
The rule is an effect of identity, it doesn’t help us determine identity.
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2. Identity of Indiscernibles
object a === object b if:
for each property P:
P(a) === P(b)
Or: If two entities share all of their properties, they are the same entity.
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Every Identity,
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Open World Ramifications (1)
Uh-‐oh!• There are infinite (potential) properties• We cannot compute indiscernibility as the for loop on the properties would run forever
len(Ψ) = ∞Indiscernibility: (∀ P∈ Ψ)(P(a) = P(b)) → a = b
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Every Identity,
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Open World Ramifications (2)
Uh-‐oh!!• There are infinite (potential) properties• [Imagine the loop could run in zero time]• Any different property would prevent identity• The likelihood of encountering indiscernibles is 1/∞ … or 0
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Every Identity,
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Open World Ramifications (3)
Uh-‐oh!!!• There are infinite (potential) properties• Any property not asserted is just not known locally and could be known elsewhere• To compute, you need complete knowledge of an infinite set of instances and infinite properties, and zero cost comparison.
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Escaping the Infinite Loop?
But …• Finite asserted properties• Finite set of publishers• Finite changes over time
Can’t we iterate over only the properties actually asserted?
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Every Identity,
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Escaping the Infinite Loop?
Still need the big-‐triplestore-‐in-‐the-‐sky with all assertions from all publishers.
Answer: Google can do it!
Google, will you run a big triplestore for us?
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Every Identity,
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Google is Disinclined to Acquiesce
to your Request
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Every Identity,
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Escaping the Infinite Loop?
Also trivial to construct a failing case:
let Ψ = [rdfs:label]a rdfs:label “Unknown”
b rdfs:label “Unknown”
Should not conclude that a owl:sameAs b
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Every Identity,
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(╯ರ ~ ರ）╯︵┻━┻
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Every Identity,
Its Ontology
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(╯ರ ~ ರ）╯︵┻━┻
angry tableflip
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Every Identity,
Its Ontology
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Practical Philosophy: John Locke
“You cannot know an entity’s identity, only its qualities.” (paraphrased)
This rings true:<urn:uuid:493650E7-‐ACBB-‐40EC-‐B141-‐4F2B6C660A71>
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More Properties, More Identity?Identity is a relationship that admits of degree:• Less than 100% identity is resemblance• The more resemblance,
the more certain the identity relationskos:exactMatch• “high degree of confidence that the concepts can be used interchangeably across a wide range of applications”
skos:closeMatch• “sufficiently similar that they can be used interchangeably in some applications”
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Every Identity,
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… its Ontology
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Every Identity,
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Resemblance?
• Given “sufficient resemblance”, we can conclude identity for practical purposes• Resemblance is via shared properties• To compute resemblance, we must understand the properties shared by candidate entities• Properties are given as predicates in LOD• Need for shared ontology?
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Porridge Too Hot? Too Cold?
Too few properties:• Sufficiency of resemblance impossible
Too many properties:• Amount of information overwhelming•More likely to run into incompatible properties
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_:Porridge crm:P51_has_former_or_current_owner
_:Papa Bear?
Understanding can then be increased by not only looking at the one entity, but where it fits within the graph of connected entities.
Now you have many resemblance problems.
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Every Identity,
Its Ontology
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Graphs unlikely to have the same shape, even with a shared ontology.Different organizations:• know different information• are from different domains• have different foci• have different contexts for the work
Graph Isomorphism
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Its Ontology
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Costs / ValuesReuse
Philosophically InfiniteAutomated: ExpensiveManual: Very Expensive
ReinventionFree as in Kittens!
Cheap, Fast, Good: Pick One!And forget about picking Cheap!
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Every Identity,
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Every Identity, its OntologyIn the absence of continuous community pressure, demonstration of value, and in-‐house expertise, even well-‐intentioned
organizations will create their own identities and ontologies for describing entities.
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Cultural Heritage Sector• Getty ULAN• Library of Congress NAF• Bibliotheque nationale de France• Deutsche National Bibliothek• British Library• ISNI• VIAF• SNAC• …
Example: Lewis CarrollIndustry
• MusicBrainz (LinkedBrainz)• IMDB (LinkedMDB)• DBPedia• WikiData• Google / Freebase• Genealogics• Quora• ReadSocial• …
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Every Identity,
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Practical Philosophy
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Its Ontology
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We could stop requiring perfection in our use of others’ data:• skos:exactMatch, not owl:sameAs• Data that is good enough• And contribute improvements!
• Persistence, not Permanence• Target is Comprehension, not Inference
Perfect is the Enemy of the Good
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Every Identity,
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We could publish a set of rules per class by which sufficiency of resemblance can be determined:•Which properties must overlap?•Which properties must be exactly the same?•Which properties can be ignored?•Which relationships must match?
Sufficiency of Resemblance
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We could publish services to make it easier to discover and reconcile our identities:• Auto-‐complete / type-‐ahead• Open Refine reconciliation• Embeddable widgets
Resemblance Services
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We could contribute to shared infrastructure for discovery and change management:• Shared infrastructure, decentralized publication• Notifications when data changes• Notifications when identities are used• With links back from the identity
• Separate publishing / discovery concerns
Shared Infrastructure
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Every Identity,
Its Ontology
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Philosophy of Practicality
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Five Laws of LOD
• Linked Open Data is for Use• Every Developer, her Data• Every Data, its Application• Save the time of the Developer
• LOD [Community] is a growing Organism
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Every Identity,
Its Ontology
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Every Identity,
Its Ontology
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Every Identity,
Its Ontology
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Every Identity,
Its Ontology
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Patrick Hochstenbach, @hochstenbach
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https://www.flickr.com/photos/harris77/3357537737
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Every Identity,
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Linked Open Usable Data!
• Strict identity matching is impossible• Target is skos:exactMatch, not owl:sameAs
• Shared ontologies are more important than precision• Target is comprehension, not inference
• Build services & infrastructure to enable reconciliation• Target audience of LOD is Developers
Pick Usable not Perfect!
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Its Ontology
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Thank You!
Rob [email protected] / @azaroth42
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Discuss!