[WS] Web Service series (ii) structure of Web Services

I found that writing logs can help me sort out my ideas. Some technologies are very effective in consolidating memory if they are written in the form of logs after they are not used for a period of time. For example, in this web service series, in order to avoid errors as much as possible, I will review the materials and learn new knowledge in this process. However, Web services involve a wide range of fields, and new technologies are emerging so quickly. Even if all the time is spent studying them, it is impossible to cover everything, just like a very thick and thick book, frequent flip leads to unexpected gains.

In the previous post, I have already mentioned what Web services are for. In this article, I want to talk about the structure of web services, that is, the protocol stack of Web Services. Protocols are the basis for communication between roles. Stack is called because these protocols are built on layer by layer. The following layer is the basis of the above layer. Just like the Relationship Between OSI Layer-7 network protocols.

Now I want to introduce some concepts: XML, SOAP, WSDL, UDDI, and BPEL4WS. XML is the abbreviation of extensible markup language, which is the basis of various web service protocols; soap is short for Simple Object Access Protocol. It is mainly used to transmit various requests and response data between service providers and users; WSDL stands for the Web Services Description Language. A service provider uses this language to publish its own Web Services for potential service users; the meaning of UDDI is the unified description discovery and Integration (Universal Description, discovery and integration ).CommunityMaintenance: service providers can register their own services on the UDDI server, and service users can browse and query the required services on the server; BPEL4WS refers to the Business Process Execution Language (Business Process Execution Language for Web Services) for Web Services. It can assemble multiple web service groups into a complete business process, represents the true power of Web Services (assembly ).

To put it simply, you may not understand some of these concepts, but it does not matter. In future posts, we will describe each concept. It should also be noted that the concepts listed here are the most widely used technologies used in actual construction and use of web services, but web services do not necessarily need to be used. Apart from XML, there are alternatives to other technologies, but they are not that popular. Let's take a look at what the web service protocol stack looks like ,.

Figure 1 web service protocol stack

The bottom layer is the service transmission layer. As shown in the figure, Web services can use multiple (OSI Application Layer) network protocols for message transmission. HTTP is the most widely used, because the HTTP request response mode is very suitable for RPC calls, SMTP is mainly used for asynchronous calls, such as subscription information.

The protocol at the service message layer defines the Message format. In this layer, almost all are based on soap. At least I have not seen examples of other protocols. Soap is based on XML, that is, soap messages must be in XML format.

The service description layer protocol is used to describe how to use this web service, the description information generally includes the data type, message format, method name, and parameter used (the name in WSDL is different. WSDL is also based on XML.

The service publishing and discovery layer protocol is used by the Registry. UDDI is the most widely used Registry. Other methods are also used in the figure.

The service Assembly layer is used to assemble web services into new services. These assembled services generally reflect certain business processes. The advantage is that the coupling between services is very small and it is easy to change. At this layer, many protocols are currently competing. BPEL4WS has some advantages.

The Protocol to be developed is relatively small than ours. The three vertical protocols on the right of the figure throughout the Web Service lifecycle. They are service management, service quality, and service security. In the future, many web services will be available for free of charge, and money-linked things must be managed to ensure quality and security. For a long time, they are all difficulties in the study of Web Services (because they involve too many benefits). Currently, Web services are well prepared in terms of functions. If they can break through these non-functional difficulties, I think Web services are not far from large-scale applications.

Figure 1 is a common protocol stack diagram. In fact, the protocol stack Diagram may not be the same because of the various web services. For example, on w3.org, XML technology is also shown in the figure, reflecting its basic position in Web Services.

Summarize the key technologies of Web Services: XML, SOAP, WSDL, UDDI, and BPEL4WS.

If you think this article is a bit abstract, it is normal because a new concept has emerged. In addition, my own understanding of Web Services is also a source and book, with insufficient project experience and lack of a macro understanding of the industry. Therefore, when writing this article, we should consider one or two points, if you are not sure, try not to write it. It doesn't matter. The following articles are about specific technologies. you can wake up :)