Select a Pattern Agnostic Capability Agnostic Context Agnostic Sub-Controller Asynchronous Queuing Atomic Service Transaction Brokered Authentication Canonical Expression Canonical Protocol Canonical Resources Canonical Schema Canonical Schema Bus Canonical Versioning Capability Composition Capability Recomposition Compatible Change Compensating Service Transaction Composition Autonomy Concurrent Contracts Contract Centralization Contract Denormalization Cross-Domain Utility Layer Data Confidentiality Data Format Transformation Data Model Transformation Data Origin Authentication Decomposed Capability Decoupled Contract Direct Authentication Distributed Capability Domain Inventory Dual Protocols Enterprise Inventory Enterprise Service Bus Entity Abstraction Event-Driven Messaging Exception Shielding Federated Endpoint Layer File Gateway Functional Decomposition Intermediate Routing Inventory Endpoint Legacy Wrapper Logic Centralization Message Screening Messaging Metadata Metadata Centralization Multi-Channel Endpoint Non-Agnostic Context Official Endpoint Orchestration Partial State Deferral Partial Validation Policy Centralization Process Abstraction Process Centralization Protocol Bridging Proxy Capability Redundant Implementation Reliable Messaging Rules Centralization Schema Centralization Service Agent Service Broker Service Callback Service Data Replication Service Decomposition Service Encapsulation Service Facade Service Grid Service Instance Routing Service Layers Service Messaging Service Normalization Service Perimeter Guard Service Refactoring State Messaging State Repository Stateful Services Termination Notification Three-Layer Inventory Trusted Subsystem UI Mediator Utility Abstraction Validation Abstraction Version Identification Overview     History     Acknowledgements     Podcasts     Notification Form     Feedback Form     Press Release #1     Press Release #2     Press Release #3 Master SOA Design Pattern Catalog     Master Pattern List (alphabetical)     Master Pattern List (by category)     Master Pattern List with Page Numbers (PDF)     Master Pattern List (Text)     Pattern Notation     Pattern Profiles     Symbol Legend     Pattern Contribution Form SOA Candidate Patterns     SOA Patterns Review Committee     Candidate Patterns Overview     Candidate Patterns List     Candidate Pattern Contribution Form     Candidate Pattern Feedback Form     SOA Pattern Template Design Pattern Basics     What's a Design Pattern?     What's a Design Pattern Language?     What's a Compound Pattern? Supplemental     SOA Patterns and Application Technologies     SOA Design Patterns Historical Influences     SOA Design Patterns and Design Principles     SOA Design Patterns and Design Granularity     Legal Resources     Design Patterns Publications     Reference Posters     SOAPrinciples.com     WhatIsSOA.com     SOA Visio Stencil Service Agent (Erl) Home > Service Messaging Patterns > Service Agent How can event-driven logic be separated and governed independently?   Problem Service compositions can become large and inefficient, especially when required to invoke granular capabilities across multiple services. Solution Event-driven logic can be deferred to event-driven programs that don¡¦t require explicit invocation, thereby reducing the size and performance strain of service compositions. Application Service agents can be designed to automatically respond to predefined conditions without invocation via a published contract. Impacts The complexity of composition logic increases when it is distributed across services, and event-driven agents and reliance on service agents can further tie an inventory architecture to proprietary vendor technology. Principles Service Loose Coupling, Service Reusability Architecture Inventory, Composition   Two service agents replace the need for the explicit invocation of utility services E and G. By deferring common logic to service agents, the overall quantity of explicitly invoked services decreases. Audio Podcast This pattern is discussed as part of the audio podcast: Versioning in SOA   Related Patterns in This Catalog Asynchronous Queuing (Little, Rischbeck, Simon), Atomic Service Transaction (Erl), Canonical Resources (Erl), Exception Shielding (Hogg, Smith, Chong, Hollander, Kozaczynski, Brader, Delgado, Taylor, Wall, Slater, Imran, Cibraro, Cunningham), Intermediate Routing (Little, Rischbeck, Simon), Message Screening (Hogg, Smith, Chong, Hollander, Kozaczynski, Brader, Delgado, Taylor, Wall, Slater, Imran, Cibraro, Cunningham), Message Metadata (Erl), Partial State Deferral (Erl), Partial Validation (Orchard, Riley), Service Messaging (Erl), State Repository (Erl), UI Mediator (Utschig, Maier, Trops, Normann, Winterberg), Utility Abstraction (Erl), Validation Abstraction (Erl) Related Patterns in Other Catalogs Event-Driven Consumer (Hohpe, Woolfe) Related Service-Oriented Computing Goals Increased Vendor Diversification Options, Reduced IT Burden This page contains excerpts from: SOA Design Patterns by Thomas Erl Foreword by Grady Booch With contributions from David Chappell, Jason Hogg, Anish Karmarkar, Mark Little, David Orchard, Satadru Roy, Thomas Rischbeck, Arnaud Simon, Clemens Utschig, Dennis Wisnosky, and others. (ISBN: 0136135161, Hardcover, Full-Color, 400+ Illustrations, 865 pages) For more information about this book, visit www.soabooks.com.

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