Understanding Service-Oriented Architecture
Looking around we see the term or acronym SOA becoming widely used, but there's not a lot of precision in the way that it's used. The World Wide Web Consortium (W3C) for example refers to SOA as 'A set of components which can be invoked, and whose interface descriptions can be published and discovered'. We see similar definitions being used elsewhere; it's a very technical perspective in which architecture is considered a technical implementation. This is odd, because the term architecture is more generally used to describe a style or set of practices—for example the style in which something is designed and constructed, for example Georgian buildings, Art Nouveau decoration or a garden by Sir Edwin Lutyens and Gertrude Jekyll .
CBDI believes a wider definition of service-oriented architecture is required. In order to reach this definition, let's start with some existing definitions, and compare some W3C offerings with CBDI recommendations. We'll begin by looking at definitions of basic Service concepts.
Service
- A Component capable of performing a task. A WSDL service: A collection of end points (W3C).
- A type of capability described using WSDL (CBDI).
A Service Definition
- A vehicle by which a consumer's need or want is satisfied according to a negotiated contract (implied or explicit) which includes Service Agreement, Function Offered and so on (CBDI).
A Service Fulfillment
- An instance of a capability execution (CBDI).
Web service
- A software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a format that machines can process (specifically WSDL). Other systems interact with the Web service in a manner prescribed by its description using SOAP messages, typically conveyed using HTTP with XML serialization in conjunction with other Web-related standards (W3C).
- A programmatic interface to a capability that is in conformance with WSnn protocols (CBDI).
From these definitions, it will be clear that the W3C have adopted a somewhat narrower approach to defining services and other related artefacts than CBDI. CBDI differs slightly insofar as not all Services are Components, nor do they all perform a task. Also CBDI recommends it is useful to manage the type, definition and fulfilment as separate items. However it is in the definition of SOA that CBDI really parts company with the W3C.
Service-Oriented Architecture:
- A set of components which can be invoked, and whose interface descriptions can be published and discovered (W3C).
When a number of different applications can all share the same structure, and where the relationships between the parts of the structure are the same, then we have what might be called a common architectural style. The style may be implemented in various ways; it might be a common technical environment, a set of policies, frameworks or practices. Example platform components of a virtual platform include:
- Host environment
- Consumer environment
- Middleware
- Integration and assembly environment
- Development environment
- Asset management
- Publishing & Discovery
- Service level management
- Security infrastructure
- Monitoring & measurement
- Diagnostics & failure
- Consumer/Subscriber management
- Web service protocols
- Identity management
- Certification
- Deployment & Versioning
Understanding Service-Oriented Architecture
http://msdn.microsoft.com/architecture/journal/default.aspx?pull=/library/en-us/dnmaj/html/aj1soa.asp
http://roadmap.cbdiforum.com
