Outline

1. Managing Service Metadata as ContextThe 2005 Istanbul International Computational Science & Engineering Conference (ICCSE2005)Mehmet S. Aktas (maktas@cs.indiana.edu)Computer Science Department INDIANA UNIVERSITY

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

3. 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

4. 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

5. 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

6. 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?

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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?

13. 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?

14. 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?

15. 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

16. 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

17. 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