【正文】 drivers for a new approach ? Heterogeneity ? Most enterprises today contain a range of different systems, applications, and architectures of different ages and technologies. ? Integrating products from multiple vendors and across different platforms were almost always a nightmare. ? But we also cannot afford to take a singlevendor approach to IT, because application suites and the supporting infrastructure are so inflexible. ? Change ? Globalization and ebusiness are accelerating the pace of change. ? Improvements in technology continue to accelerate, feeding the increased pace of changing customer requirements. The business drivers for a new approach ? As a result, business anizations are evolving ? from the vertical, isolated business divisions of the 1980’s and earlier ? to the horizontal businessprocessfocused structures of the 1980’s and 1990’s ? towards the new ecosystem business paradigm. Business services now need to be ponentized and distributed. ? There is a focus on the extended supply chain, enabling customer and partner access to business services. The business drivers for a new approach ? Questions: ? How do I make my IT environment more flexible and responsive to the ever changing business requirements? ? How can we make those heterogeneous systems and applications municate as seamlessly as possible? ? How can we achieve the business objective without bankrupting the enterprise? ? Currently many IT executives and professionals alike believe that now we are getting really close to providing a satisfactory answer with serviceoriented architecture. The business drivers for a new approach ? In order to alleviate the problems of heterogeneity, interoperability and ever changing requirements, such an architecture should provide a platform for building application services with the following characteristics: ? Loosely coupled ? Location transparent ? Protocol independent ? Based on such a serviceoriented architecture, a service consumer does not even have to care about a particular service it is municating with because the underlying infrastructure, or service “bus”, will make an appropriate choice on behalf of the consumer. ? The infrastructure hides as many technicalities as possible from a requestor. Particularly technical specificities from different implementation technologies such as J2EE or .NET should not affect the SOA users. ? We should also be able to reconsider and substitute a “better” service implementation if one is available, and with better quality of service characteristics. Objectoriented analysis and design ? Objectoriented analysis and design ? Larman describes the essence of the objectoriented analysis and design as considering “a problem domain and logical solution from the perspective of objects (things, concepts, or entities)” in ? Applying UML and Patterns – An Introduction to ObjectOriented Analysis and Design. ? Jacobson, et al, define these objects as being “characterized by a number of operations and a state that remembers the effects of these operations” in ? ObjectOriented Software Engineering: A Use Case Driven Approach. ? In objectoriented analysis, such objects are identified and described in the problem domain, while in objectoriented design, they are transitioned into logical software objects that will ultimately be implemented in a objectoriented programming language. ? With objectoriented analysis and design, certain aspects of the object (or group of objects) can be encapsulated to simplify the analysis of plex business scenarios. ? Certain characteristics of the object(s) can also be abstracted so that only the important or essential aspects are captured, in order to reduce plexity. Componentbased design ? Componentbased design is not a new technology. It is naturally evolved from the object paradigm. ? Packaged solution suites can also be encapsulated as such “ponents”. ? Once the anization achieves a higher level of architectural maturity based on distinctly separate functional ponents, the applications that support the business can be partitioned into a set of increasingly larger grained ponents. ? Components can be seen as the mechanism to package, manage and expose services. ? They can use a set of technologies in concert: Largegrained enterprise ponents, that implement businesslevel usecases, can be implemented using newer objectoriented software development in bination with legacy systems. Serviceoriented design ? In ComponentBased Development for Enterprise Systems, Allen includes the notion of services, describing a ponent as ? “an executable unit of code that provides physical blackbox encapsulation of related services. Its service can only be accessed through a consistent, published interface that includes an interaction standard. A ponent must be capable of being connected to other ponents (through a munications interface) to a larger group”. ? A service is generally implemented as a coursegrained, discoverable software entity that exists as a single instance and interacts with applications and other services through a loosely coupled, messagebased munication model. SOA ? SOA的理念最初由全球最具權威的 IT研究與顧問咨詢公司 Gartner于 1996年提出： ? “ A serviceoriented architecture is a style of multitier puting that helps anizations share logic and data among multiple applications and usage modes.”。 ? “一種應用程序體系結構，在這種體系結構中，所有功能都定義為獨立的服務，這些服務帶有定義明確的可調(diào)用接口，可以以定義好的順序調(diào)用這些服務來形成業(yè)務流程”。 Serviceoriented design ? important serviceoriented terminology: ? Services: Logical entities, the contracts defined by one or more published interfaces. ? Service provider: The software entity that implements a service specification. ? Service consumer (or re