Managing Service
Metadata as Contex
Outline
p
Introduction
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Problem Statement,
Hypothesis, Design Goals
p
Literature Survey,
Research Issues
p
Milestones
Context i
Gaggle of Services
p
Def:
"Context is any information that can be used to
characterize the situation of an entity, where an entity can be a
person, place, or computational object.“ Dey A. et al, 1999
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Context is metadata associated to both services and their
activities
p independent of any interaction
§ static context, dynamic context
p generated as result of interaction
§ information associated to an activity or session
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Gaggle of Services
n are set of actively collaborating managed services for a particular
common goal
Motivations
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Current Grid Information Services provide information
describing services independent of their interactions.
p
We need management of all information associated with
services for;
n
correlating activities of widely distributed services
n
management of events especially in multimedia collaboration
n enabling uniform query capabilities to both conversation-based or
monolog context information
p “Give me list of services satisfying C:{a,b,c..} QoS requirements and
participating S:{x,y,z..} sessions”
n providing information to enable
p real-time replay/playback and
Application Use Domain
p
Workflow-style distributed application:
Geographic
Information System Grid
n sensor grid data services generates events when a certain magnitude
event occurs
n firing off various codes, filtering, analyzing raw data, generating images,
maps
n needs a distributed context management to correlate workflow activities
p
Characteristics of domain
n any number of widely distributed services can be involved n conversation metadata
p transient
Problem Statement
What is a novel process of building Information
Services, maintaining dynamic session-related
Hypothesis
p A fault-tolerant, high performance, scalable information system
n maintaining widely distributed dynamically generated metadata for
Gaggle of Services
n providing uniform interface to context information
p utilization of existing Grid Information Services for
interaction-independent context to improve search capabilities
n enabling coordination of widely distributed services in Gaggles
p workflow-style Grid applications
n enabling distributed event management and various capabilities for
A/V conferencing applications
p discovery of entities in a session
Architectural Design Goals
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Key Design Goals of our Design
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scalability
p with respect to #
p widely distributed services
n
performance
p high responsiveness, reduced access latency
n
fault tolerance
p high availability of information p robust to replica crashes
n
flexibility
WS-CA
WS-Context - Key Concepts
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WS Composite Application Framework (WS-CAF)
n WS-Context, WS-Coordination, WS-Transaction Mngmt.
p
WS Context
n defines context, context service and mapping on SOAP n shared data to correlate service activities
n context information dependent on the type of the activity
p transactional activity: the URI of the coordinator in a session
n context service maintains associated context
n participants of an activity register with context service for lifecycle of
WSRF, WS-Metadata Exchange
Key Concepts
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WSRF (Web Service Resource Framework)
n defines standard interfaces and behaviors for distributed system
integration
n enables every service to expose state data for query, update n supports resource oriented approach for stateful interactions
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WS-Metadata Exchange
n provides mechanism for sharing information about the capabilities
of individual Web services
p WS-Policy, WSDL
n allows querying a WS Endpoint to retrieve metadata about what to
know to interact with them
Limitations in
Specifications for Service Communication
p
WSRF does not actually accomplish state management by just
enabling access and update rights
n heterogeneous service environment n workflow-style applications
p
WSRF, WS-Metadata Exchange models service metadata
private to a service
n does not scale in managing activities of multiple services
n WS-Metadata Exchange defines only how to access
interaction-independent metadata
p
WS-Context is promising it has limitations
n simple framework for context management n limited query capability
Research Issues
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Recap on key design goals:
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scalability, performance, fault tolerance
p
research issues related replicating dynamic metadata
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deployment (dynamic vs. static replication)
p Where to place replicas of given context metadata? p What are the properties of new location must meet? p How to know if replica location stable?
Research Issues II
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consistency
p What is the appropriate consistency model?
p How do replicas exchange replica updates in what direction?
p
performance
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efficient metadata access
p How to choose a replica server to best serve client request?
Research Issues III
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scalability
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load balancing strategies
p How to manage load balancing?
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other research issues
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session recovery
p How to enable session recovery?
n
uniform interface to context
Milestones
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Uniform Update and Query (search, discovery)
Services
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Sequencer Service
n
ensures that an order is imposed on actions/events that
Milestones II
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Storage (Replication) Service
n decide # and placement of replicas n enable autonomous behavior
n support robust behavior for replica crashes
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Access (Request Distribution) Service
n distribute request among object replicas
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Expeditor Service
n generalized caching mechanism
Summary
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Here we addresses following problems
n Lack of support in Grid Information Services for context
(session-related dynamic metadata) management to correlate activities in workflow-style applications:
p by providing a novel approach for management of widely distributed,
shared session-related dynamic metadata
n Lack of support in Grid Information Services to provide distributed
session management:
p by providing distributed event management system enabling session
failure recovery or replay/playback capabilities
n Lack of search capabilities in Grid Information Services:
p by providing uniform search interface to both interaction independent and
