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Managing Metadata in Service Architectures

Managing Metadata in Service Architectures. Mehmet S. Aktas Advisor: Prof. Geoffrey C. Fox. Outline. Introduction Motivation Requirements Research Issues Architecture Performance Evaluation Conclusions Contribution. Context as Service Metadata. Context interaction-independent

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Managing Metadata in Service Architectures

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  1. Managing Metadata in Service Architectures Mehmet S. Aktas Advisor: Prof. Geoffrey C. Fox

  2. Outline • Introduction • Motivation • Requirements • Research Issues • Architecture • Performance Evaluation • Conclusions • Contribution

  3. Context as Service Metadata • Context • interaction-independent • slowly varying, quasi-static service metadata • interaction-dependent • dynamically generated metadata as result of interaction of services • information associated to a single service, or a session (service activity) or both • Dynamic Grid/Web Service Collections • loosely assembled collections of services • assembled to support a specific task • generate metadata and have limited life-time

  4. Motivating Cases • Multimedia Collaboration Grids • Global Multimedia Collaboration System- Global MMCS • widely distributed services, • session service metadata, session metadata, stream-specific metadata • mostly read-only • Workflow-style applications in Geographical Information System/Sensor Grids • Pattern Informatics (PI) – UC Davis, Interdependent Energy Infrastructure Simulation System (IEISS) – LANL • widely distributed services • conversationmetadata, transient • multiple writers

  5. Problems with Grid Information Services • Standardization and Unification Issues • Customized Grid Information Services • Differences in application requirements • Thick clients • Performance and Centralization Issues • Low performance • Low fault tolerance • Dynamic Metadata Management Issues • Point-to-point service communication approaches

  6. Requirements for Grid Information Services • Greater Interoperability • Unified platform for communication • Shared communication protocol • Thin clients • Greater Capabilities • High Performance • Fault-tolerant • Dynamic Grid/Web Service Collections • Distributed state management • Collaboration session management

  7. Research Issues I • Unification of Grid Information Services • How to combine different information services? • Federation of Grid Information Services • What is a common data model and communication protocol? • Flexibility and extensibility • Accommodating broad range of application domains • read-dominated, read/write dominated • Ability to add/support more information services • Interoperability • Being compatible with wide range of applications

  8. Research Issues II • Performance • Efficient centralized metadata management strategies • high performance and persistency • Efficient decentralized metadata management strategies • Efficient request distribution strategies • Adaptation to instantaneous client-demand changes • Fault-tolerance • Efficient replica-content creation strategies • Consistency • How to provide consistency across the copies of the same data?

  9. Hybrid Grid Information Service • Unification • Uniform Access • Extensibility • Interoperability • Extended UDDI • WS-Context • Federation • Unified Schema • Query/Publish XML API

  10. UDDI instance WS-Context instance Unified schema instance 10 of 34

  11. Decentralized • Fault-tolerant • Efficient distribution • Look-ahead caching • Consistency enforced 11 of 34

  12. Support for interaction-independent metadata: Extended UDDI Service • It supports different types of metadata • Geographical Information System Metadata Catalog (functional metadata) • User-defined metadata ((name, value) pairs) • It enables advanced query capabilities • Geo-spatial queries • Metadata oriented queries • Domain independent queries • It provides additional capabilities • Up-to-date service registry information (leasing) • Dynamic aggregation of capabilities of services • Ex: geospatial capabilities

  13. Support for interaction-dependent metadata: WS-Context Service • Context Manager Service • Data model and communication protocol • Session-related metadata • It supports Dynamic Web Service Collections • Support for distributed state based systems • collaboration grids • workflow-style grids • It provides various capabilities • Asynchronous communication capability • Up-to-date service registry information (leasing)

  14. Support for federated service metadata: Unified Information Service • Federating Grid Information Services • Unified data model and communication protocol • Extended UDDI, WS-Context and Glue Schemas • Approach taken • Union of schemas vs. separate schemas • Reuse common concepts • Ex1: business, session, site => category • Combine disjoined concepts • Ex1: UDDI’s tModel • It enables hybrid query capabilities • “Give me list of services satisfying C:{a,b,c..} QoS requirements and participating S:{x,y,z..} sessions”

  15. Federating Grid Information Services Subscriber Publisher Collaboration Grid Sensor Grid WSDL WSDL HYBRID Service HYBRID Service WS-Context Ext-UDDI Database Database Topic Based Publish-Subscribe Messaging System

  16. Features of the Distributed System • Cache Strategy • Memory-in storage • Access Distribution • Redirecting client request to an appropriate replica server • Look-ahead caching • Moving/replicating metadata to where they wanted • Replica Content Placement • Replicating data on an appropriate replica server • Consistency enforcement • Ensuring all replicas of a data to be the same 16 of 34

  17. Tuple Spaces & Publish-Subscribe Paradigms • Publish-Subscribe paradigm • Message based asynchronous communication • Participants are decoupled both in space and in time • Open source NaradaBrokering software • topic based publish/subscribe messaging system • Tuple Spaces paradigm [Gelernter-99] • a data-centric asynchronous communication paradigm • communication units are tuples (data structure) • JavaSpaces [Sun Microsystems]- object oriented implementation specification

  18. Caching Strategy • Light-weight implementation of JavaSpaces • Data sharing, associative lookup, and persistency • Integrated caching capability for all types of service metadata • Ex: UDDI-type, WS-Context-type, Unified Schema-type metadata • We assume that today’s servers are capable of holding such small size metadata in cache. • All metadata accesses happen in memory • Persistency • All metadata is backed-up into appropriate Information Service back-end every so often for persistency

  19. Persistency investigation 19 of 34

  20. Performance investigation

  21. Message rate scalability investigation

  22. Message size scalability investigation

  23. AccessDistributionLook-ahead Caching • Broadcast-based request dissemination • Pub-sub system for message broadcast • Broadcast requests only to those servers that can answer • No need to keep track of metadata locations • Dynamic migration/replication • [Rabinovich et al, 1999] • Popular copies are moved/replicated where they wanted • Autonomous decisions, self-awareness

  24. Access Distribution ExperimentTest Methodology Time = T1 + T2 + T3 T1 T2 T3

  25. Distribution experiment result • Overhead of access distribution is only few milliseconds. • Continuous access distribution operation does not degrade the performance. • The overhead of distribution remains the same regardless of the network distances between nodes.

  26. Dynamic Replication PerformanceTest Methodology Time = T1 + T2 + T3 T1 T2 T3

  27. The decrease in average latency shows that the algorithm manages to move replica copies to where they wanted.

  28. Replica content placementConsistency enforcement • Replica-content placement • Each node keeps information about other servers • Selection of Replica Server(s) • Selection policy based on a) geographical (proximity) and b) topical (number of topics) information • Consistency Enforcement - Primary-copy approach • Update distribution: updates labeled with synchronized timestamps reflected (unicast) to primary-copy • Update propagation: primary-copy pushes (broadcast) updates only to those replica servers holding the context Hybrid Service 1 Hybrid Service 1 Hybrid Service 2 Hybrid Service 3 Hybrid Service 4

  29. Fault-tolerance experiment Testing Setup Time = T1 + T2 + T3 T1 T2 T3

  30. Fault-tolerance experiment result • Overhead of replica creation is only few milliseconds. • Continuous replica creation operation does not degrade the performance. • Overhead of replica creation increases in the order of milliseconds as the fault-tolerance level increase.

  31. Consistency Enforcement ExperimentTest Methodology Time = T1 + T2 + T3 T1 T2 T3

  32. Consistency Enforcement Test Result • Overhead of consistency enforcement is few milliseconds. • Continuous operation does not degrade the performance. • The cost of consistency enforcement remains the same regardless of distribution of the network nodes.

  33. Conclusions • Efficient centralized metadata management strategies • TupleSpaces Paradigm based memory-in storage • Efficient decentralized metadata strategies • TupleSpaces & Pub-Sub communication paradigms • Distribution • Replication for fault-tolerance • Replication for performance • Consistency Enforcement

  34. Contributions • Unified Grid Information Service Architecture • Flexible and extendable architecture • Support for High Performance and Fault-tolerance • Uniform access to all kinds of service metadata • Federated Grid Information Service Architecture • Unified data model and communication protocol • Support for both interaction independent and conversation-based service metadata • Support for greater interoperability • Efficient decentralized metadata systems can be built by integrating TupleSpaces and Publish-Subscribe paradigms • Fault-tolerance, distribution and consistency can be succeeded with few milliseconds system processing overhead. • Self-awareness can be achieved in decentralized metadata management. • Communication among services can be achieved with efficient mediator metadata strategies • A metadata management approach for Dynamic Web/Grid Service Collections • Collective operations such as queries on subsets of all available metadata in service conversation.

  35. Selected Publication List focusing on a) Metadata, b) Information Services, and c) Metadata Discovery • Mehmet S. Aktas, Geoffrey Fox, Marlon Pierce, Information Services for Dynamically Assembled Semantic Grids [SKG-05, 2005] • Mehmet S. Aktas, Geoffrey Fox, Marlon Pierce, Managing Dynamic Metadata as Context [ICCSE, 2005] • Mehmet S. Aktas et al., Web Service Information Systems and Applications [GGF-16, 2006] • Mehmet S. Aktas, Geoffrey C. Fox, Marlon Pierce, Fault Tolerant High Performance Information Services for Dynamic Collections of Grid and Web Services [FGCS Journal, 2006] • Mehmet S. Aktas, Sangyoon Oh, Geoffrey C. Fox, Marlon Pierce, XML Metadata Services [SKG-2006, Concurrency and Computation: Practice and Experience Journal-2007] • Mehmet S. Aktas, Marlon Pierce, and Geoffrey C.Fox, Designing Ontologies and Distributed Resource Discovery Services for an Earthquake Simulation Grid [ GGF11, 2004] • Mehmet S. Aktas, M. Pierce, G. Fox, and D. Leake , A Web based Conversational Case-Based Recommender System for Ontology aided Metadata Discovery [GRID Workshop -2004] • Sangyoon Oh, Mehmet S. Aktas, Geoffrey C. Fox, Marlon Pierce, Architecture for High-Performance Web Service Communications Using an Information Service [WSEAS Journal -2006]

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