i-esa'08 berlin1 logical foundations for the infrastructure of the information market heather,...
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I-ESA'08 Berlin 1
Logical Foundations for the Infrastructure of the Information Market
Heather, Michael, Livingstone, David, & Rossiter, Nick,
CEIS, Northumbria University, Newcastle, UK
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Outline of Talk• Unstructured and Structured Data
• Implications of Gödel– Relational Model
– Interoperability
• Difficulties of SQL with Gödel
• Need in interoperability– higher order formalism without axiom or number
• Applied category theory– topos (with composition, adjointness)
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Simple data is well-handled
• Information Systems– Well established for simple data
• Unstructured– e.g. web pages, natural language, images
• Structured– e.g. relational database
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Natural and Structured Data Types
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Interoperability
• Relatively easy between natural (unstructured) data:– natural language + translators– images + human eye
• Difficult between structured data:– schema is reductionist– inter-communication is problematical
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Underlying Difficulties• Relational Databases
– based on first-order predicate calculus (FOPC)
• Efforts by Codd and Date– to keep narrowly within FOPC
• atomic data (first normal form)• nested data is encapsulated• operations are within standard first-order set theory
– arguments are sets
• But interoperability requires higher-order operations
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Effect of Gödel• Gödel showed that:
– Both intensional and extensional systems that rely on axiom and number are undecidable
– But FOPC is complete
• Therefore– Strict relational model and calculus is complete and
decidable– Higher order systems that rely on axiom and
number are not complete and decidable
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Inherent Difficulty of Interoperability
• As interoperability is always higher order– from mapping functions to functions
• Interoperability is outside natural applicability of set theoretic methods
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Particular Problems with SQL
• SQL has compromised the pure relational model
• So SQL poses special problems in interoperability– Variants in its implementation– Not faithful to relational model – Closed world assumption– Nulls
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Variants of SQL
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Not Faithful to Relational Model
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Problems with Nulls
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Nulls offend Gödel
• Use of nulls gives– maybe outcome to some queries– so result from query is not decidable
• Codd persisted with nulls
• Date has more recently removed them from the ‘pure’ relational model– not offend Gödel– keep within FOPC
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Formalism for Interoperability• If set theory in general is undecidable and not
complete, what might be used?
• Category Theory (CT) has its focus and strengths in higher order logic e.g. functors– Pure CT is though axiomatic – n-categories rely on number– so both offend Gödel– Applied CT, based on a process view and of
composition, appears to not offend Gödel
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Composition in CTa) with Gödel; b) against Gödel
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Adjointness between two Composition Triangles
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Composition Triangles in Detaila) unit of adjunction ; b) co-unit of adjunction
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Architecture for InteroperabilityEffective Topos T with interoperability between categories L and R in context of
category C
Figure 8
T = SoS (system of systems)
L, R are interoperating systems
C is context ofinteroperation
Arrowsrepresentadjointness
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Summary• Implications of Gödel
– Pure relational model in itself, as first-order predicate calculus, is complete and decidable
– Interoperability is though higher order– Set theory, as defined with axiom and number, is not
complete and decidable for higher order– Applied category theory, without axiom or number,
seems appropriate
• Example architecture given for applied category theory with topos and composition