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Universität Innsbruck Leopold Franzens making semantics real Copyright 2006 DERI Innsbruck www.deri.at LarCK Workshop, ISWC/ASWC 2007 - Busan, Korea Jul 2, 2022 Towards Scalable Information Spaces Reto Krummenacher , Elena Simperl, Dieter Fensel
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Universität Innsbruck Leopold Franzens Copyright 2006 DERI Innsbruck LarCK Workshop, ISWC/ASWC 2007 - Busan, Korea 16-Feb-14 Towards Scalable.

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Page 1: Universität Innsbruck Leopold Franzens Copyright 2006 DERI Innsbruck  LarCK Workshop, ISWC/ASWC 2007 - Busan, Korea 16-Feb-14 Towards Scalable.

Universität InnsbruckLeopold Franzens

making semanticsreal. Copyright 2006 DERI Innsbruck www.deri.at

LarCK Workshop, ISWC/ASWC 2007 - Busan, KoreaApr 10, 2023

Towards Scalable Information Spaces

Reto Krummenacher, Elena Simperl, Dieter Fensel

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making semanticsreal.2 LarCK Workshop, ISWC/ASWC 2007 - Busan, KoreaApr 10, 2023

Background: Triple Space Computing

Semantic Spacerd

rd

out

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Background: Triple Space Computing

Host / Kernel

Host / Kernel Host / Kernel

Host / Kernel

Host / Kernel

InformationSpace

InformationSpace

InformationSpace

InformationSpace

InformationSpace

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Triple Space Computing at Web Scale

• The Web is distributed, heterogeneous, dynamic, and open.

• Required is a Triple Space platform which copes with these principles at Web scale.

• Classical guarantees encountered in closed environments cannot longer hold.

• Adaptation of the functional properties publish and retrieve is required.

• Feasible non-functional guarantees must be determined from a scalability perspective

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Outline

1. (Non-) Functional Properties and Their Impact on Scalability of Information Spaces

2. Scalability-driven Trade-Offs

3. Levels of Scalability for Semantic Space Middleware

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Two Dimensions

• There are two dimensions to a middleware that influence its scalability

– The exposed functionality - the service delivered to the clients - the functional properties.

– The internal behavior of the system that is not obvious or visible to clients at interaction time - the non-functional properties (NFP).

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Functionals (1/2)

• Publishing information– Writing of one or more RDF triples into an identifiable space.– No guarantee about when the triple is available and

persistently stored.

• Retrieving information– Reading triples by template/query.– No guarantees about when and if a match is returned.– An empty result set does not imply that no matching triple is

available.– Retrieval is possible from an identifiable space, or from any

available spaces.

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Functionals (2/2)

• Query complexity– Ranging from triple patterns <:tripcom ?p ?o> to arbitrarily

complex queries. – Query resolution (reasoning).

• Explicit vs. inferred data– Publication at data level – no reasoning, multiple copies.– Retrieval at knowledge level – inference, materialization, only

„one“ copy.• Local reasoning vs. distributed reasoning.

• Transactions– E.g. when publishing sets of triples within an atomic

operation.

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Non-Functionals

• Security – retrieve,publish• Fault-tolerance – retrieve,publish• Availability – retrieve,publish• Reliability – retrieve,publish

• Completeness – retrieve• Correctness – retrieve• Consistency – retrieve• Durability – publish

• Response time – retrieve,publish• Scalability – retrieve,publish

data/query related

TS related dependability

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making semanticsreal.

Technical Means for NFP

TS Kernel

replication

triplespace 1

TS Kernel

segment 1cluster

segment 2cluster

Primary CopyPrimary Copy Backup

triplespace 2

TS Kernel Primary

Copy

distribution

• Redundancy– duplication of processes (n-out-of-

m, n < m).

• Recovery– Re-installation of previous system

state.

• Load balancing– decentralization of processes

• by replicating data.• by distributing data (partitioning,

clustering).

10 LarCK Workshop, ISWC/ASWC 2007 - Busan, KoreaApr 10, 2023

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NFP and their Realization (1/3)

• Fault-Tolerance– Redundancy: prevention, 1-out-of-2– Recovery

• Availability– Load balancing: 1-out-of-N

• Reliability– Redundancy: prevention, 2-out-of-3

• Completeness– No distribution of data

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NFP and their Realization (2/3)

• Consistency– No replication: no system-caused inconsistency

• Correctness

– No false-positives, a query engine issue, completeness

• Durability– Recovery: persistency is given by storage

• Response time– Load balancing

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making semanticsreal.

NFP and their Realization (3/3)

• Scalability– The trade-offs between non-functional properties and

between functionals and non-functionals need to be analyzed in order to to achieve a feasible level of scalability.

– The appropriate configurations for the desired behavioral and structural realization and the corresponding scalability level has to be selected.

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Scalability Trade-Offs

Correctness CompletenessPrecision vs. recall

Completeness AvailabilityLoad balancing by distribution

Consistency AvailabilityLoad balancing by replication

Consistency Fault ToleranceReplication could be hidden

Reliability Response TimeCompleteness Response TimeConsistency Response TimeDurability Response Time

Non-local writing results in latency

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Scalability Levels

• Depending on the desired functionality and non-functionality, the space middleware has different possibilities to provide a scalable infrastructure.

The richer functionality the middleware provides, the less can be guaranteed about the non-functional properties and scalability.

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Scalability Levels: Discussion (1/3)

• Simplest approach - proved and tested with respect to scalability– The target space is indicated by a resolvable URL– Distribution is client-driven– Discovery by use of a DNS-like procedure– Ensures at least local scalability

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Scalability Levels: Discussion (2/3)

• Most complex approach – likely not scalable– Access to spaces without indication of a URL– (Knowledge-driven) retrieval on the entire Semantic

Web– Query forwarding, distributed discovery of relevant

spaces– Distributed reasoning to integrate distributed

information sources/spaces or large scale (local) reasoning after transfer of triples

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Scalability Levels: Discussion (3/3)

• Loosening classical IR guarantees is of benefit to achieve scalability– Access to space(s) without indication of a URL– Best effort retrieval – no completeness– No guarantees about consistency– Rather data than knowledge-driven

• Performance– Search scope– Discovery strategy

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Conclusions

• Semantic spaces offer at least local scalability and local completeness.

• Scalability at global scale requires the management of scalability trade-offs.

• However…– “The times of 100% complete and correct solutions are gone.”

[D. Fensel, STI International 2007]

– „incomplete, incorrect but requested!“ [D. Fensel, IEEE Intelligent Systems

22(6) 2007]

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making semanticsreal.22 LarCK Workshop, ISWC/ASWC 2007 - Busan, KoreaApr 10, 2023

Thank you.

Universität InnsbruckLeopold Franzens

making semanticsreal.LarCK Workshop, ISWC/ASWC 2007 - Busan, Korea

Copyright 2006 DERI Innsbruck www.deri.at Apr 10, 2023