Web Services Interview Questions

17 September, 2018


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Web Service Interview Questions

Following are some of the most frequently asked Web Service interview questions in the interview, here are the answers for them.

Explain Web Services?

A Web Service can be defined as an application component for communication or say exchanging information between two applications over the network. Web services basically work on client server model where web services are easily accessible to client applications over the network.

To enable communication between various applications, web services take the help of open standards like XML (for data tagging), SOAP (for message transferring) and WSDL (to denote service availability).

What is the difference between SOA and a web service?

SOA (Service-Oriented Architecture) is an architectural pattern that makes possible for services to interact with one another independently.

Web Services is a realization of SOA concept, that leverages XML, JSON, etc. and common Internet protocols such as HTTP(S), SMTP, etc. SOA is a system-level architectural style that tries to expose business. WOA is an interface-level architectural style that focuses on the means by which these service capabilities are exposed to consumers.

What is SOAP?

SOAP (Simple Object Access Protocol) is a transport protocol for sending and receiving requests and responses on XML format, which can be used on top of transport protocols such as HTTP, SMTP, UDP, etc.

What is the difference between a REST web service and a SOAP web service?

Below are the main differences between REST and SOAP web service

-REST supports different formats like text, JSON and XML; SOAP only supports XML; -REST works only over HTTP(S) on a transport layer; SOAP can be used different protocols on a transport layer; -REST works with resources, each unique URL is some representation of a resource; SOAP works with operations, which implement some business logic through different interfaces; -SOAP based reads can’t be cached, for SOAP need to provide caching; REST based reads can be cached; -SOAP supports SSL security and WS-security(Web Service-security); REST only supports SSL security; -SOAP supports ACID (Atomicity, Consistency, Isolation, Durability); REST supports transactions, but it is neither ACID compliant nor can provide two phase commit.

What is WSDL?

WSDL (Web Services Description Language) is an XML format for describing web services and how to access them.

What is MTOM?
MTOM (Message Transmission Optimization Mechanism) is a mechanism for transmitting large binary attachments with SOAP messages as raw bytes, allowing for smaller messages.

WSDL is the language that UDDI uses.

What is XOP?
XOP (XML-binary Optimized Packaging) is a mechanism defined for the serializationof XML Information Sets that contain binary data, as well as deserialization back into the XML Information Set.
Define web service protocol stack and its layers?
Web service protocol stack consists of 4 layers. This can be described as follows 1) Service transport: This is the first layer which helps in transporting XML messages between various client applications. This layer commonly uses the below-mentioned protocols:
HTTP(Hypertext Transport Protocol) SMTP(Simple Mail Transport Protocol) FTP(File Transfer Protocol) BEEP(Block Extensible Exchange Protocol)
2) XML messaging: This layer is based on the XML model where messages are encoded in common XML format which is easily understood by others. This layer includes
XML-RPC SOAP(Simple Object Access Protocol)
3) Service description: This layer contains description like location, available functions, and data types for XML messaging which describes the public interface to a specific web service. This layer includes:
WSDL(Web Service Description Language)
4) Service discovery: This layer is responsible for providing a way to publish and find web services over the web. This layer includes:
UDDI(Universal Description, Discovery, and Integration)

HTTP stands for Hyper Text Transfer Protocol.

XML-RPC is a simple protocol that uses XML messages to perform RPCs.

Following are the features of SOAP −
SOAP is a communication protocol.SOAP is for communication between applications. SOAP is a format for sending messages. SOAP is designed to communicate via Internet. SOAP is platform independent. SOAP is language independent. SOAP is simple and extensible. SOAP allows you to get around firewalls. SOAP will be developed as a W3C standard.

There are three specific security issues with web services −

  • Confidentiality
  • Authentication
  • Network Security

Web services manageability is defined as a set of capabilities for discovering the existence, availability, health, performance, usage, as well as the control and configuration of a web service within the web services architecture. As web services become pervasive and critical to business operations, the task of managing and implementing them is imperative to the success of business operations.

WSDL is an XML-based language for describing web services and how to access them.

Following are the features of UDDI − UDDI is a specification for a distributed registry of web services. UDDI is platform independent, open framework. UDDI can communicate via SOAP, CORBA, and Java RMI Protocol. UDDI uses WSDL to describe interfaces to web services. UDDI is seen with SOAP and WSDL as one of the three foundation standards of web services. UDDI is an open industry initiative enabling businesses to discover each other and define how they interact over the Internet.  
What are the core layers in Web Service Protocol Stack?
The Web Service Protocol Stack is still evolving, but currently has four main layers −
Service Transport XML Messaging Service Description Service Discovery

This is any consumer of the web service. The requestor utilizes an existing web service by opening a network connection and sending an XML request.

Enlist few advantages of web services?

We have already discussed web services, its architecture, components. Now, let us see some its advantages

-Every application is now on the internet and it the web service which provides some sort of required functionality to the client applications. -Web services help in exposing the existing functionalities over the network to help other applications to use in their programs. -It has features like ‘Interoperability’ which determines the communication between various applications, sharing of data as well as services among themselves. -Web services use the standardized web service protocol stack for communication which consists of 4 layers namely, Service Transport, XML messaging, Service description and Service discovery. -It has the feature of the low cost of communication because of the usage of SOAP (Simple Object Access Protocol) over HTTP protocol. -Easy to deploy, integrate and is reusable. -Allows simple integration between different feature as a part of loose coupling feature.

Explain BEEP?

BEEP stands for Blocks Extensible Exchange Protocol. BEEP is determined as building new protocols for the variety of applications such as instant messaging, network management, file transfer etc. It is termed as new Internet Engineering Task Force (IETF) which is layered directly over TCP. It has some built-in features like



Error handling

Handshake Protocol

Explain the advantages of RESTful web services?

Enlisted below are the advantages of RESTful web services

-They are considered as language and platform independent as these can be written in any programming language and can be executed on any platform. -REST is lightweight protocol and is considered as fast because of less consumption of bandwidth and resources. -It supports multiple technologies and different data formats like plain text, XML, JSON, etc. -It has loosely coupled implementation and can be tested easily over browsers.

Explain different HTTP methods supported by RESTful web services?

Enlisted below are some common HTTP methods along with their functions that are supported by RESTful web services

GET: Read-only access to the resource.

PUT: Creation of new resource.

DELETE: Removal of a resource.

POST: Update of an existing resource.

OPTIONS: Get supported operations on the resource.

HEAD: Returns HTTP header only, nobody.

For designing a secure RESTful web service, what are the best factors that should be followed?

As HTTP URL paths are used as a part of RESTful web service, so they need to be secured. Some of the best practices include the following

Perform validation of all inputs on the server from SQL injection attacks.

Perform user’s session based authentication whenever a request is made.

Never use sensitive data like username, session token password, etc through URL. These should be passed via POST method.

Methods like GET, POST, PUT, DELETE, etc should be executed with proper restrictions.

HTTP generic error message should be invoked wherever required.

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