Managing Service Metadata as Context The 2005 Istanbul International Computational Science & Engineering Conference (ICCSE2005) Mehmet S. Aktas Computer Science Department INDIANA

2 of 17 Outline  Introduction  Problem Statement, Hypothesis, Design Goals  Literature Survey, Research Issues  Milestones  Summary

3 of 17 Context in Gaggle 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 of 17 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 of 17 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 of 17 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 of 17 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 of 17 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 of 17 WS-CAF WS-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 of 17 WSRF, WS-Metadata Exchange Key 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 of 17 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 of 17 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 of 17 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 of 17 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 of 17 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 of 17 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 of 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