[Paper Review] Formal Model of Web Service Composition: An Actor-Based Approach to Unifying Orchestration and Choreography

Yong Wang|arXiv (Cornell University)|Dec 3, 2013

Service-Oriented Architecture and Web Services48 references3 citations

TL;DR

This paper proposes AB-WSCL, an actor-based language for web service composition that unifies orchestration and choreography through a formal semantics grounded in concurrent rewriting theory. By modeling services, orchestrations, and choreographies as actors, the approach establishes a natural, compositionally verified relationship between components, enabling both design-time verification and runtime execution with formal correctness guarantees.

ABSTRACT

Web Service Composition creates new composite Web Services from the collection of existing ones to be composed further and embodies the added values and potential usages of Web Services. Web Service Composition includes two aspects: Web Service orchestration denoting a workflow-like composition pattern and Web Service choreography which represents an aggregate composition pattern. There were only a few works which give orchestration and choreography a relationship. In this paper, we introduce an architecture of Web Service Composition runtime which establishes a natural relationship between orchestration and choreography through a deep analysis of the two ones. Then we use an actor-based approach to design a language called AB-WSCL to support such an architecture. To give AB-WSCL a firmly theoretic foundation, we establish the formal semantics of AB-WSCL based on concurrent rewriting theory for actors. Conclusions that well defined relationships exist among the components of AB-WSCL using a notation of Compositionality is drawn based on semantics analysis. Our works can be bases of a modeling language, simulation tools, verification tools of Web Service Composition at design time, and also a Web Service Composition runtime with correctness analysis support itself.

Motivation & Objective

• To establish a natural, formally grounded relationship between web service orchestration (WSO) and choreography (WSC) in cross-organizational service composition.
• To design a runtime architecture that integrates WSO, WSC, and web services into a unified, concurrent execution model.
• To provide a formal semantics for the AB-WSCL language using concurrent rewriting theory to ensure correctness and compositionality.
• To enable practical tooling—modeling, simulation, verification, and runtime execution—through mappings to standard XML-based web service specifications.
• To demonstrate the expressiveness and correctness of the approach via a formal analysis of message interactions and component composition.

Proposed method

• Model web services, orchestrations, and choreographies as actors in a concurrent system, leveraging the intrinsic concurrency of the actor model.
• Define AB-WSCL as a domain-specific language based on actor systems, supporting message-passing semantics between WS, WSO, and WSC components.
• Establish formal semantics for AB-WSCL using concurrent rewriting theory, enabling precise modeling of interaction sequences and state transitions.
• Use the compositionality concept to formally verify relationships between WSO and WS, WS and WS, and WSO and WSO through interaction semantics.
• Define mappings between AB-WSCL and standard web service specifications (WSDL, WS-BPEL, WS-CDL) to ensure interoperability and practical applicability.
• Validate the approach through a running example of a book purchase process, demonstrating message flow and state transitions across actors.

Experimental results

Research questions

• RQ1 How can orchestration and choreography be formally unified within a single runtime architecture for web service composition?
• RQ2 What formal semantics can be defined for an actor-based language that supports both orchestration and choreography while preserving compositionality?
• RQ3 How can interactions between web service orchestrations, web services, and choreographies be modeled and verified for correctness?
• RQ4 To what extent can AB-WSCL serve as a foundation for design-time tools (modeling, simulation, verification) and runtime execution?
• RQ5 What is the relationship between AB-WSCL and existing XML-based web service specifications such as WSDL, WS-BPEL, and WS-CDL?

Key findings

• The actor-based approach naturally unifies orchestration and choreography by modeling all components as actors, enabling a consistent and concurrent execution model.
• Formal semantics based on concurrent rewriting theory provide a rigorous foundation for AB-WSCL, ensuring correctness and enabling formal verification of component interactions.
• Compositionality is formally established through interaction semantics, proving well-defined relationships between WSOs, WSs, and WSCs.
• Mappably to WSDL, WS-BPEL, and WS-CDL, AB-WSCL supports bidirectional translation, enabling integration with existing web service ecosystems.
• The language is both simple and expressive, supporting modeling, simulation, verification, and runtime execution within a single formal framework.
• The approach enables both design-time validation and runtime execution with correctness guarantees, demonstrating practical applicability in real-world service composition.