OASIS (the Organization for the Advancement of Structured Information Standards)对SOA的定义如下：
Definition 1 (Service-Oriented Architecture [1]) A Service-Oriented Architecture (SOA)
is paradigm for organizing and utilizing distributed capabilities that may be under the control
of different ownership domains. It provides a uniform means to offer, discover, interact with
and use capabilities to produce desired effects consistent with measurable preconditions and
expectations.
SOA的三个组成部分：service provider；service requestor；discovery agency
Web Service定义：
Definition 2 (Web Service [44]) A Web service is a software system designed to support
interoperable machine-to-machine interaction over a network. It has an interface described in
a machine-processable format (specifically WSDL [62]). Other systems interact with the Web
service in a manner prescribed by its description using SOAP [90] messages, typically conveyed
using HTTP with an XML [51] serialization in conjunction with other Web-related standards.
Web Service Composition 服务组合的定义：
Web Service Composition which is the ability to aggregate multiple services into a single composite service that would provide a certain functionality, which otherwise cannot be provided by a single service.
Web Service Composition的分类：
1、orchestration
Orchestration describes how multiple services can interact by exchanging messages including the business logic and execution order of the interactions from the perspective of a single endpoint (i.e., the orchestrator).
2、Choreography
message exchanges and interactions that occur between multiple process endpoints,
两种实现方式：manually and (semi-) automatically.
服务组合面临的问题和挑战：Research Questions and Challenges
1、Service Specifications
2、Service Discovery
3、Verification and Validation of Composition
4、Service Specification Reformulation
5、Analysis for Compatibility and Replaceability
6、Execution Management and Monitoring
7、Tooling Support
Techniques based on Formal Methods
Formal Methods定义：
Formal Methods [47] is an area of study that provides a language for describing a software
artifact (e.g., specifications, design, source code) such that formal proofs are possible, in principle, about properties of the artifact so expressed.
Web Service Adaptation
Adaptation定义：
Adaptation by definition implies to “something” that is changed or changes so as to become suitable to a new or special application or situation.
Web Service Adaptation的分类：
In the context of Web services, adaptation refers to two basic ideas: static adaptation and dynamic adaptation.
（1）static adaptation
The problem of static adaptation is concerned with analyzing techniques that are typically applied during a service composition process to (i) automatically build adapters to enable service mediation, and (ii)modify the specification of the goal (or desired) service for generation of a feasible composition.
（2）dynamic adaptation
On the other hand, the problem of dynamic adaptation is concerned with developing methods that allow the execution model of a composite service to be modulated depending on run-time conditions (e.g., Quality of Service requirements).
Labeled Transition System定义：
A labeled transition system (LTS) is a tuple (S,−>, s0, SF ) where S is a set of states represented by terms, s0 is the start state, SF is the set of final states and −> is the set of transition relations of the form s−> t
To determine such “similarity” between services, we introduce two variants of equivalence of LTSs: strong equivalence (or bisimulation) and weak equivalence (or simulation), which identify equivalent LTSs in the presence of guarded transitions with input/output actions, atomic actions and unobservable actions .
服务组合问题描述：
Given a goal service Tg and a set of available component services T1, T2, . . . , Tn, solving the service composition problem entails identifying a composition of the necessary component services that realizes the functionality of Tg. In the setting of orchestration-based composition (Figure 1.4(a)), this entails generating a mediator TM which realizes the functionality of Tg by orchestrating the necessary interactions among the selected component services.
Thus, solving the service composition problem entails to constructing a mediator which can enable interaction between the component services so as to yield a behavior that is strong equivalent (bisimilar) to that of the desired goal service.
Web Service Dependency Matrix
Given an LTS describing a service, there are two types of dependencies:
1. Data Dependency: if the input of an action a or the valuation of a guard g depends on the output of another action b, then a or g is said to be data dependent on b.
2. Control Dependency: if the execution of an action a or the valuation of a guard g depends on the valuation of another guard g', then a or g is said to be control dependent on g'.
