Aurora Borealis

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Aurora Borealis
http//www.ics.forth.gr/pleiades/projects/Aurora/a
urora.html
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An Infrastructure for Service-level Management in
Distributed Work Sessions
Manolis Marazakis PhD Thesis Public
Defense March 10, 2000 Research Area Distributed
Systems
Department of Computer Science
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The Problem

• Provision of new services over the Internet
• Integrated travel package
• airlines, hotels, cars, reservations
• Tourist information services
• recommend nearby restaurants amusement parks
• Information correlation services
• find rank WWW pages
• Multi-organization experiment management
• global climate studies

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Is it difficult ?

• Global-scale interoperability
• Autonomy
• Severe restrictions on control of foreign systems
• Large-scale distribution
• Variable delays, partial failures
• Increasingly interdependent systems
• Mutual commitments, delegation

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Is it significant ?

• Service composition
• Adding value to existing systems
• The Web
• Pervasive access medium
• forces all to establish presence
• Presence gives potential for external
  transactions
• Shortcomings of existing approaches
• Assumptions contradicting autonomy

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Network-Centric Applications
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A Motivating Example Recommending WWW Links

• Collect links on given topic
• Rank links
• Filter out non-promising links
• Present results

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Composition of Services
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Thesis

• In order to facilitate reuse and combination of
  services from independent authorities, it is
  essential to support automatic sequencing of
  service-level agreements, and reliable tracking
  of interaction state. An appropriate component
  platform needs to be in place to enable SLAs.

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Service Level Agreement (I)

• expected/promised behavior of services
• methods, parameters, results, exceptions
• estimates of performance metrics
• access control restrictions
• compensating actions
• Inspection manipulation of controls

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Service-Level Agreement (II)

• More predictable dependable services
• Respects autonomy of providers
• SLA mediates all interactions with service

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Aurora in the Protocol Stack
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Contributions (I)

• Component platform
• Design implementation
• Service-level agreements
• Log/monitor system, service contract object
  framework
• Extensions to OMG CORBA
• Component/container framework
• Event notification services
• Directory service for component/services metadata

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Contributions (II)

• Design implementation of a scripting language
• Access to component/container services
• Event-Condition-Action rules (WHEN, WHENEVER)
• Demonstrator systems
• Yahoo AltaVista recommendation service
• E-commerce environment, agreements in order
  handling

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Related Work (I)

• WfMC family emphasis on state management
• Process models, work items lists, roles,
  resources
• State transitions upon events
• generated by outcome of work assignments
• DB-managed process state
• Lacks service-level management
• Assumes WFMS to be the sole work coordinator

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Related Work (II)

• Exotica/FMQM (IBM Research, 1995-1997)
• Partitioning of process model (using a compiler)
• Persistent queuing system (MQSeries) for
  integration
• WIDE (EU Project, 1997-)
• Use of DB triggers to support ECA rules
• Research on exception handling
• Lack service-level management
• Rely on proprietary services for integration

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Related Work (III)

• CHAIMS (U. Stanford, 1996-1998)
• A language for supporting exclusively composition
• Compiler for decomposing a synchronous invocation
  into phases
• SWAP (IETF Internet Draft, 1998)
• request protocol for managing long-running
  activities
• contributed to WfMC-TC-1023 (2000)
• Lack service-level management
• Assume static or manual sequencing

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Related Work (IV)

• INCAs (Barbara et al, 1996)
• Self-contained units of work (mobile agents)
• HADAS (Technion Institute, 1995-1999)
• explicit links between sites
• automated installation of component packages
• Lack service-level management

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Related Work (V)

• Numerous business object frameworks
• Oracles NCA (1997)
• IBMs San Francisco Project (1998), and Component
  Broker (1998)
• BEAs M3 (1998 / evolution of Tuxedo TP monitor)
• SUNs Enterprise Java Beans (1998)
• Combination of shared services and standard
  callback interfaces
• Lack service-level management
• Assume single authority

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Related Work (VI)

• Collaboration Management Infrastructure (MCC,
  1999-)
• descriptions of services, currently for dynamic
  binding
• COYOTE (IBM Research, 1998)
• Compiler-assisted generation of contract wrappers
• Reliance on stubs undermines autonomy

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Related Work Distributed Objects

• No standard model for server-side components
• interoperable components (e.g. CORBA/IIOP, DCOM)
• No standard way of accessing basic services
• inflexible dependencies on run-time services
• Important developments
• OMG CORBA Components Specification (draft 1999)
• EJB (1998) persistent state transactions
• SUNs Jini architecture (1998) join discovery
• HPs eSpeak architecture (1999) E-Services vision

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Technical Details Components, Containers,
Requests
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The Architecture of Aurora
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Interoperability Problems
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Component Model Concepts

• Overlapping but different concerns
• component development
• application assembly
• application deployment
• component hosting
• server platform
• Container a component hosting environment
• Shield from server-specific dependencies
• references to services
• notify components when actions are needed

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Container Run-Time
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Service State Transitions
Minimal requirements for request processing state
exposure.
Providers may expose more detailed FSM.
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Service Control Model
Separation of concerns Provider vs. Requester
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Request Management
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Workflow Model
Shift of emphasis from state/product to
satisfaction of commitments
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WfMC Reference Model
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Work Session Framework
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Access Control

• Actions
• use an interface
• monitor an event
• invoke an interface method
• Clients need explicit permissions to assume
  roles
• Security credentials (ID, public key, authority)
• associated with work session participants through
  directories
• Access Controller
• Permissions/restrictions to assume roles
• Enforcement of access control policy

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SLA Framework (I)
Normal flow order fulfilled within deadline
Provider
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SLA Framework (II)
Deviation missed order deadline
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Case Study
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Order Tracking Workflow (I)

• Services by independent providers
• Products catalogue
• Inventory
• Shopping basket
• Payment processor
• Order tracking
• Feedback log
• Two implementations
• OMG jointFlow
• Aurora work session framework

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Order Tracking Example (II)
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Order Tracking Example (III)

• Aurora services used
• asynchronous event notifications (FSM)
• log/monitor system
• access control for setting order state
• service-level agreements
• deadline for shipping an order
• deadline for claiming a refund
• compensations when returning products

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Technical Details Scripting
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Configuration Example
corba_init HERMES
corba_resolve csrv container_init reqMgr csrv
demo1 set
yahoo_pkgK load_component_package_drep reqMgr
yahooPkg yahooPkg_dkey
set yahoo_iK init_component_instance r
eqMgr yahoo_pkgK yahoo_init_args
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Composition Example
set yahoo_rid request_issue reqMgr callerID
cbSpec yahoo_iK ifN methodN slaSpec ifrK
yahoo_args set yahoo_results request_wait
reqMgr yahoo_rid set altavista_args lindex
yahoo_results 0
set altavista_rid
request_issue reqMgr callerID
cbSpec altavista_iK ifN methodN slaSpec
ifrK altavista_args
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Reactive Rule Example
proc condition1 varList action examine
status_taskA, status_taskB to determine
value of res if res 1 action
varList corba_resolve prompter set
varSpecA rule_variable state_taskA REQUIRED
statusA prompter set varList list varSpecA
varSpecB set rk1 when rule1 varList
condition1 action1
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Conclusions Perspective
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Conclusions

• Network-centric applications
• large-scale distribution
• autonomy
• dynamic environment
• Aurora
• service-level agreements
• component/container framework
• Extensions to OMG CORBA

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Composing Service-Level Agreements

• Provider P0 uses services of P1, P2
• Each provider offers its own contracts
• SLA(P0), SLA(P1), SLA(P2)
• P2 changes parameters of SLA(P2)
• How to propagate changes ?
• In real-time

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Supporting Thin Clients

• Service access devices of limited capabilities
• PDAs, 3rd-generation cellular phones
• Limited CPU, bandwidth memory
• Intermittent connectivity
• Their number will soon surpass that of PCs
• Support for transactional applications ?

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Aurora Australis
http//www.ics.forth.gr/pleiades/projects/Aurora/a
urora.html