What is a Service?

Service refers to any software component that provides functionality and is an independent building block that can be integrated together collectively to
represent an application.

Each service is responsible for its specified role in its own domain. In the business sense the service focuses on a specific business function or possibly a group of functions. This model allows for the creation of isolated units of business functionality that can be easily reused throughout development. The loosely bound services help to provide freedom within the architecture.

In the past service orientation was created using services though increasingly today SOA (Service Oriented Architecture) refers to the use of XML Web services. This is because of the vendor neutral implementation and its interface/implementation provide as an ideal model for SOA.

What is a Web Service?

In 2000, the World Wide Web Consortium (W3C) accepted a submission for the Simple Object Access protocol (SOAP). This XML-based messaging format established a transmission framework for inter-application or inter-service communication via HTTP. As a vendor neutral technology, SOAP provided an attractive alternative to traditional proprietary protocols, such as CORBA (Common Object Request Broker Architecture) and DCOM (Distributed Component Object Model).

In the following year, W3C has accepted and published the WSDL specification. WSDL (Web Service Description Language) is implemented through XML and acts as the interface in the interface/implementation model of Web service. It is essentially a language that is used to describe the interface of the Web service.

The interface is further supplemented by the Universal Description, Discovery and Integration (UDDI) specification. The UDDI much like a yellow page directory allows users to perform dynamic searches on the directory for a specific service implementation.

Since then, XML Web services has received industry wide acceptance. The support for XML Web services has furthered the popularity and importance of a service oriented design principle.

Purpose of Metadata

Metadata has many uses. Here are some of them:

• Metadata removes the need for header and library files when compiling, because all the information about the referenced types/members is contained in one file along with the IL that implements those type/members. Compilers can read metadata directly from managed modules.
• Visual Studio uses metadata to help you write code. Its IntelliSense feature parses metadata to tell you what methods a type offers and what parameters that method expects.
• The CLR code verification process uses metadata to ensure that your code performs only “safe” operations.
• Metadata allows an object’s fields to be serialized into a memory block, remoted to another machine, and then deserialized, recreating the object and its state on the remote machine.
• Metadata allows the garbage collector to track the lifetime of objects. For any object, the garbage collector can determine the type of the object, and from the metadata it knows which fields within that object refer to other objects