The internet connects millions of computers worldwide, forming a vast network. Within this network, the World Wide Web relies on Web Services as a fundamental method for applications to communicate. A web service acts as a standardized way for different software applications, whether they are clients or servers, to exchange messages and data over a network. Think of it as a software module designed to perform specific tasks and make those functionalities accessible across the web, particularly within cloud computing environments. When a client application needs a specific function, it can invoke a web service to deliver that functionality.
In essence, a web service is a set of open protocols and standards that enable data exchange between diverse applications and systems. These services facilitate communication between software programs written in various languages and running on different platforms. This exchange occurs over computer networks like the internet, similar to how processes communicate within a single computer.
Any software, application, or cloud technology utilizing standard web protocols such as HTTP or HTTPS to connect, interact, and exchange data messages – typically in XML (Extensible Markup Language) format – is categorized as a web service. The beauty of web services lies in their ability to bridge the gap between programs developed in different languages. They achieve this by enabling data exchange between clients and servers through a standardized web service interface. A client initiates communication by sending an XML request to the web service, which then responds with an XML response.
Web Service Operation Diagram
This diagram illustrates the basic operation of a web service. A client sends requests to a server hosting the web service. These requests are essentially remote procedure calls (RPC), invoking specific methods offered by the web service. For example, imagine an e-commerce platform like Flipkart offering a web service to display item prices. The front-end of the application, perhaps built with .Net or Java, can communicate with this web service regardless of the programming language used to develop the service itself. The key element in this interaction is the data exchange format: XML.
XML (Extensible Markup Language) acts as a universal language understood by various programming languages. It’s analogous to HTML but focuses on data structure rather than presentation. This common language allows applications written in different languages to communicate seamlessly. To transmit XML data, web services commonly use SOAP (Simple Object Access Protocol). Data is sent via standard HTTP, and a SOAP message encapsulates the XML data being transmitted between the web service and the application. Because the message content is in XML, the client application interacting with the web service can be developed in virtually any programming language.
Core Functions of Web Services
Web services are designed with specific functionalities in mind, making them powerful tools for distributed computing. Key functions include:
- Accessibility via Internet and Intranet: Web services can be accessed through both the public internet and private intranet networks, making them versatile for various deployment scenarios.
- Standardized XML Messaging Protocol: They rely on XML as a standardized messaging protocol, ensuring interoperability and platform independence.
- Operating System and Programming Language Independence: Web services are designed to be independent of specific operating systems and programming languages, promoting seamless integration across diverse technological environments.
- Self-Describing through XML Standards: Using XML standards, web services are self-describing, meaning their capabilities and interfaces can be understood by other systems without prior knowledge.
- Simple Location Mechanism: Web services can be easily located through straightforward mechanisms, enabling dynamic discovery and utilization.
Essential Components of Web Services
The foundation of most web services platforms rests on XML and HTTP. Several key components are crucial for their operation:
SOAP (Simple Object Access Protocol)
SOAP, or Simple Object Access Protocol, is a transport-agnostic messaging protocol. It’s a cornerstone of web services, built upon sending XML-formatted data as SOAP messages. Each message includes an XML document that adheres to a specific structure but allows flexibility in content. A SOAP document must have a root element called the <Envelope> element, which is divided into two main parts: a header and a body. The header contains routing information, guiding the XML document to the correct recipient. The body contains the actual message content. A significant advantage of SOAP in web services is its reliance on HTTP, the standard web protocol, for message transmission, ensuring broad compatibility and ease of use.
UDDI (Universal Description, Discovery, and Integration)
UDDI, standing for Universal Description, Discovery, and Integration, serves as a standard for publishing and discovering online web services. It provides a framework for service providers to advertise their services and for client applications to find them. UDDI essentially acts as a directory service, allowing clients to discover WSDL files, which describe the capabilities of a web service. Think of UDDI as a repository where WSDL files are stored, enabling client applications to explore the functionalities offered by various web services. The UDDI registry holds essential information about each online service, much like a phone directory provides names, addresses, and phone numbers. This allows client applications to locate the web service they need.
WSDL (Web Services Description Language)
WSDL, or Web Services Description Language, is crucial for understanding and utilizing web services. Before a client application can use a web service, it needs to know two key things: the service’s location and its capabilities. WSDL provides this information through an XML-based file. This WSDL file describes what the web service does and how to interact with it. By reading the WSDL document, a client application can understand the service’s location (endpoint) and the operations it supports, enabling it to correctly invoke the web service. WSDL ensures that clients have the necessary information to effectively communicate with and utilize web services.
Key Features and Characteristics of Web Services
Web services possess several defining features that contribute to their effectiveness and widespread adoption:
(a) XML Based: Web services fundamentally rely on XML for data representation and message transport. This XML foundation eliminates dependencies on specific networks, operating systems, or platforms. The use of XML ensures high interoperability for applications built upon web services.
(b) Loosely Coupled: A client application using a web service is not tightly bound to that service. The web service provider can evolve and change its internal implementation without disrupting the client’s ability to interact with it. This loose coupling contrasts with tightly coupled systems where changes in one component necessitate changes in others. Loose coupling makes software systems more maintainable, adaptable, and facilitates integration between different systems.
(c) Synchronous and Asynchronous Capabilities: Web services can support both synchronous and asynchronous communication. Synchronous operations require the client to wait for the web service to complete its task before proceeding. In contrast, asynchronous operations allow the client to initiate a task and continue with other operations without waiting for an immediate response. Asynchronous capabilities are crucial for enabling loosely coupled systems and improving responsiveness in certain scenarios.
(d) Coarse-Grained Operations: Unlike object-oriented systems that often expose fine-grained methods, web services typically offer coarse-grained operations. This means that web services expose functionalities at a higher level of abstraction, representing business-level operations rather than individual technical methods. This approach aligns better with business needs and simplifies client interactions.
(e) Support for Remote Procedure Calls (RPC): Web services enable clients to invoke procedures, functions, and methods on remote systems using XML-based protocols. This RPC capability allows for distributed computing and accessing functionalities across networks. Web services can either directly offer their own services or act as intermediaries, translating incoming invocations to other enterprise components like Enterprise JavaBeans (EJBs) or .NET components.
(f) Document Exchange Support: XML’s strength in representing data and complex entities makes web services ideal for document exchange. These documents can range from simple address information to complex business documents like purchase orders or requests for quotations. Web services facilitate the seamless exchange of these documents, streamlining business processes and data integration.
Advantages of Utilizing Web Services
Adopting web services brings numerous advantages to businesses and developers:
(a) Exposing Business Functions Over the Internet: Web services allow businesses to expose specific functionalities and code components to client applications or end-users over the internet. Because they utilize HTTP, these functionalities become accessible from virtually anywhere. In today’s interconnected world, where applications are increasingly web-based, this capability is immensely valuable, enabling businesses to offer services and integrate with partners and customers seamlessly.
(b) Enhanced Interoperability: Web services are designed to enable communication and data exchange between diverse applications, regardless of their underlying technology platforms. For instance, a .NET application can seamlessly interact with Java web services and vice versa. This interoperability is a core strength, breaking down technology silos and promoting application integration across heterogeneous environments.
(c) Cost-Effective Communication: By leveraging SOAP over HTTP, web services can utilize existing, low-cost internet infrastructure for communication. While SOAP over HTTP is common, web services can also be implemented using other reliable transport protocols like FTP, offering flexibility and cost-efficiency.
(d) Adherence to Standard Protocols: Web services operate based on well-defined industry protocols. The entire web service protocol stack, encompassing service transport, XML messaging, service description, and service discovery, relies on standardized protocols. This standardization ensures consistency, interoperability, and ease of adoption.
(e) Reusability: A single web service can be utilized concurrently by multiple client applications. This reusability maximizes efficiency, reduces development effort, and promotes a service-oriented architecture where functionalities are shared and reused across different applications and systems.
Sample Questions and Answers:
Question 1. What protocol is used when you upload a file to the internet?
Answer:
The protocol commonly used for uploading files to a server over the internet is FTP (File Transfer Protocol). FTP client applications enable users to interact with FTP servers to access data and services. Users need an internet connection and an FTP client application to use FTP servers effectively.
Question 2. Why are web services necessary?
Answer:
In today’s business landscape, web applications are built using diverse programming platforms, including Java, .Net, Angular JS, Node.js, and others. Often, these applications need to communicate and work together. However, ensuring seamless communication between applications written in different programming languages can be complex. Web services address this challenge by providing a common platform for applications written in different languages to connect and exchange data effectively, enabling interoperability across diverse technology stacks.
Question 3. What level of security is recommended for web services?
Answer:
Web services often require a higher level of security than standard Secure Socket Layer (SSL). Solutions like Entrust Secure Transaction Platform can provide this enhanced security. This level of security is crucial for web services to ensure reliable transactions and protect sensitive and confidential information exchanged between applications.
