More Services

Key Points

References

Key Concepts

Web Services framework overview

https://www.guru99.com/web-service-architecture.html

Web service summary

The client would invoke a series of web service calls via requests to a server which would host the actual web service.

These requests are made through what is known as remote procedure calls. Remote Procedure Calls(RPC) are calls made to methods which are hosted by the relevant web service.

As an example, Amazon provides a web service that provides prices for products sold online via amazon.com. The front end or presentation layer can be in .Net or Java but either programming language would have the ability to communicate with the web service.

The main component of a web service is the data which is transferred between the client and the server, and that is XML. XML (Extensible markup language) is a counterpart to HTML and easy to understand the intermediate language that is understood by many programming languages.

WS benefits

1. common protocol to pass messages – XML

2. exposes services to clients for reusable services

3. supports security options

4. uses existing TCP protocols

WS types

1. SOAP web services.

2. RESTful web services.
   
   

SOAP-messages

soap messages have an envelope with a header and body

• The header contains the routing data which is basically the information which tells the XML document to which client it needs to be sent to.

• The body will contain the actual message.

The header element can contain information such as authentication credentials which can be used by the calling application. It can also contain the definition of complex types which could be used in the SOAP message. By default, the SOAP message can contain parameters which could be of simple types such as strings and numbers, but can also be a complex object type.

<xsd:complexType>     
 <xsd:sequence>       
 	<xsd:element name="Tutorial Name" type="string"/>         
  	<xsd:element name="Tutorial Description"  type="string"/>
  </xsd:sequence>
</xsd:complexType>

SOAP frameworks marshal and unmarshal the messages

SOAP example in VB

https://www.guru99.com/soap-simple-object-access-protocol.html

WSDL

The WSDL file is again an XML-based file which basically tells the client application what the web service does. By using the WSDL document, the client application would be able to understand where the web service is located and how it can be utilized.

UDDI

UDDI is a standard for describing, publishing, and discovering the web services that are provided by a particular service provider. It provides a specification which helps in hosting the information on web services.

Agent - Broker - Service architecture

1. Provider - The provider creates the web service and makes it available to client application who want to use it.
2. Requestor - A requestor is nothing but the client application that needs to contact a web service. The client application can be a .Net, Java, or any other language based application which looks for some sort of functionality via a web service.
3. Broker - The broker is nothing but the application which provides access to the UDDI. The UDDI, as discussed in the earlier topic enables the client application to locate the web service.

Connecting client to a service

1. Publish - A provider informs the broker (service registry) about the existence of the web service by using the broker's publish interface to make the service accessible to clients
2. Find - The requestor consults the broker to locate a published web service
3. Bind - With the information it gained from the broker(service registry) about the web service, the requestor is able to bind, or invoke, the web service.

Web services features

1. xml based
2. soap message has a header and a body
3. loosely coupled
4. synch or asynch
5. supports rpc
6. supports document exchange
7. wsdl defines how to bind to a service

Potential Value Opportunities

Potential Challenges

Candidate Solutions

Step-by-step guide for Example

sample code block

Recommended Next Steps

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