Managing Service Metadata as

Context

The 2005 Istanbul International Computational Science & Engineering

Conference (ICCSE2005)

Mehmet S. Aktas (maktas@cs.indiana.edu)Computer Science Department

INDIANA UNIVERSITY

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Outline Introduction Problem Statement, Hypothesis, Design Goals Literature Survey, Research Issues Milestones Summary

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Context inGaggle of Services 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

Context is metadata associated to both services and their activities

independent of any interaction static context, dynamic context

generated as result of interaction information associated to an activity or session

Gaggle of Services are set of actively collaborating managed services for a

particular common goal generate events as result of interactions are very small part of the whole Grid

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Motivations Current Grid Information Services provide

information describing services independent of their interactions.

We need management of all information associated with services for; correlating activities of widely distributed services management of events especially in multimedia

collaboration enabling uniform query capabilities to both conversation-

based or monolog context information “Give me list of services satisfying C:{a,b,c..} QoS

requirements and participating S:{x,y,z..} sessions” providing information to enable

real-time replay/playback and session failure recovery capabilities

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Application Use Domain Workflow-style distributed application:

Geographic Information System Grid sensor grid data services generates events when a

certain magnitude event occurs firing off various codes, filtering, analyzing raw data,

generating images, maps needs a distributed context management to correlate

workflow activities Characteristics of domain

any number of widely distributed services can be involved conversation metadata

transient multiple writers

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Problem Statement

What is a novel process of building Information Services, maintaining dynamic session-related metadata of widely distributed services, providing uniform interface to both interaction-independent and conversation-based context?

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Hypothesis A fault-tolerant, high performance, scalable information

system maintaining widely distributed dynamically generated

metadata for Gaggle of Services providing uniform interface to context information

utilization of existing Grid Information Services for interaction-independent context to improve search capabilities

enabling coordination of widely distributed services in Gaggles

workflow-style Grid applications enabling distributed event management and various

capabilities for A/V conferencing applications discovery of entities in a session enabling playback/replay capabilities, enabling session failure recovery

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Architectural Design Goals Key Design Goals of our Design

scalability with respect to # widely distributed services

performance high responsiveness, reduced access latency

fault tolerance high availability of information robust to replica crashes

flexibility accommodate broad range of application domains read-dominated, read/write dominated

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WS-CAFWS-Context - Key Concepts WS Composite Application Framework (WS-CAF)

WS-Context, WS-Coordination, WS-Transaction Mngmt. WS Context

defines context, context service and mapping on SOAP shared data to correlate service activities context information dependent on the type of the

activity transactional activity: the URI of the coordinator in a

session context service maintains associated context participants of an activity register with context service

for lifecycle of that activity

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WSRF, WS-Metadata ExchangeKey Concepts

WSRF (Web Service Resource Framework) defines standard interfaces and behaviors for

distributed system integration enables every service to expose state data for query,

update supports resource oriented approach for stateful

interactions WS-Metadata Exchange

provides mechanism for sharing information about the capabilities of individual Web services

WS-Policy, WSDL allows querying a WS Endpoint to retrieve metadata

about what to know to interact with them defines request/response message pairs to retrieve

WS metadata

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Limitations in Specifications for Service Communication WSRF does not actually accomplish state

management by just enabling access and update rights heterogeneous service environment workflow-style applications

WSRF, WS-Metadata Exchange models service metadata private to a service does not scale in managing activities of multiple services WS-Metadata Exchange defines only how to access

interaction-independent metadata WS-Context is promising it has limitations

simple framework for context management limited query capability does not address distributed management aspects of

context metadata

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Research Issues Recap on key design goals:

scalability, performance, fault tolerance research issues related replicating dynamic

metadata deployment (dynamic vs. static replication)

Where to place replicas of given context metadata? What are the properties of new location must meet? How to know if replica location stable? How can we provide tailored replication based on R/W

properties?

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Research Issues II consistency

What is the appropriate consistency model? How do replicas exchange replica updates in what

direction?

performance efficient metadata access

How to choose a replica server to best serve client request?

How to avoid performance degradation due to repetitive queries?

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Research Issues III scalability

load balancing strategies How to manage load balancing?

other research issues session recovery

How to enable session recovery? uniform interface to context

How to provide a uniform interface to context?

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Milestones Uniform Update and Query (search,

discovery) Services

Sequencer Service ensures that an order is imposed on

actions/events that take place in a session

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Milestones II Storage (Replication) Service

decide # and placement of replicas enable autonomous behavior support robust behavior for replica crashes

Access (Request Distribution) Service distribute request among object replicas

Expeditor Service generalized caching mechanism reduce storage access due to repetitive queries

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Summary Here we addresses following problems

Lack of support in Grid Information Services for context (session-related dynamic metadata) management to correlate activities in workflow-style applications:

by providing a novel approach for management of widely distributed, shared session-related dynamic metadata

Lack of support in Grid Information Services to provide distributed session management:

by providing distributed event management system enabling session failure recovery or replay/playback capabilities

Lack of search capabilities in Grid Information Services: by providing uniform search interface to both interaction

independent and conversation-based context enabling service discovery through events