20 SOAP Interview Questions (ANSWERED) Developers Must Kill

A Service Oriented Architecture (SOA) is basically defined as an architectural pattern consisting of services. Here application components provide services to the other components using communication protocol over the network. This communication involves data exchanging or some coordination activity between services.

Some of the key principles on which SOA is based are mentioned below

• The service contract should be standardized containing all the description of the services.
• There is loose coupling defining the less dependency between the web services and the client.
• It should follow Service Abstraction rule, which says the service should not expose the way functionality has been executed to the client application.
• Services should be reusable in order to work with various application types.
• Services should be stateless having the feature of discoverability.
• Services break big problems into little problems and allow diverse subscribers to use the services.

SOAP stands for Simple Object Access Protocol. SOAP is an XML based industry standard protocol for designing and developing web services. Since it’s XML based, it’s platform and language independent. So our server can be based on JAVA and client can be on .NET, PHP etc. and vice versa.

WSDL stands for Web Service Description Language. WSDL is an XML based document that provides technical details about the web service. Some of the useful information in WSDL document are:

• method name,
• port types,
• service end point,
• binding,
• method parameters etc.

WSDL stands for Web service Description Language. It is a simple XML document which comes under the Service Description layer of Web Service Protocol Stock and describes the technical details or locates the user interface to web service. Few of the important information present in WSDL document are

• Method name
• Port types
• Service end point
• Method parameters
• Header information
• Origin, etc

Web Services work on client-server model and when it comes to choose between SOAP and REST, it all depends on project requirements. Let’s look at some of the conditions affecting our choice:

• Do you know your web service clients beforehand? If Yes, then you can define a contract before implementation and SOAP seems better choice. But if you don’t then REST seems better choice because you can provide sample request/response and test cases easily for client applications to use later on.
• How much time you have? For quick implementation REST is the best choice. You can create web service easily, test it through browser/curl and get ready for your clients. What kind of data format are supported? If only XML then you can go with SOAP but if you think about supporting JSON also in future then go with REST.

SOAP web services have all the advantages that web services has, some of the additional advantages are:

• WSDL document provides contract and technical details of the web services for client applications without exposing the underlying implementation technologies.
• SOAP uses XML data for payload as well as contract, so it can be easily read by any technology.
• SOAP protocol is universally accepted, so it's an industry standard approach with many easily available open source implementations.

Some of the disadvantages of SOAP protocol are:

• Only XML can be used, JSON and other lightweight formats are not supported.
• SOAP is based on the contract, so there is a tight coupling between client and server applications.
• SOAP is slow because payload is large for a simple string message, since it uses XML format.
• Anytime there is change in the server side contract, client stub classes need to be generated again. Can’t be tested easily in browser

To ensure reliable transactions and secure confidential information, web services requires very high level of security which can be only achieved through Entrust Secure Transaction Platform. Security issues for web services are broadly divided into three sections as described below

1) Confidentiality: A single web service can have multiple applications and their service path contains a potential weak link at its nodes. Whenever messages or say XML requests are sent by the client along with the service path to the server, they must be encrypted. Thus, maintaining the confidentiality of the communication is a must.

2) Authentication: Authentication is basically performed to verify the identity of the users as well as ensuring that the user using the web service has the right to use or not? Authentication is also done to track user’s activity. There are several options that can be considered for this purpose

• Application level authentication
• HTTP digest and HTTP basic authentication
• Client certificates

3) Network Security: This is a serious issue which requires tools to filter web service traffic.

There are basically 2 different approaches available for developing SOAP-based web services. These are explained as follows

• Contract-first approach: In this approach, the contract is defined first by XML and WSDL and then java classes are derived from the contract.
• Contract-last approach: In this approach, java classes are defined first and then the contract is generated which is usually the WSDL file from the java class.

“Contract-first” method is the most preferred approach.

UDDI is acronym for Universal Description, Discovery and Integration. UDDI is a directory of web services where client applications can lookup for web services. Web Services can register to the UDDI server and make them available to client applications.