What is the difference between an XML Schema and WSDL?
The difference I noticed is that WSDL contains XSD and in WSDL we can declare operations, but not in XSD. Is that correct?
WSDL (Web Services Description Language) describes your service and its operations - what is the service called, which methods does it offer, what kind of in parameters and return values do these methods have?
It's a description of the behavior of the service - it's functionality.
XSD (Xml Schema Definition) describes the static structure of the complex data types being exchanged by those service methods. It describes the types, their fields, any restriction on those fields (like max length or a regex pattern) and so forth.
It's a description of datatypes and thus static properties of the service - it's about data.
XSD defines a schema which is a definition of how an XML document can be structured. You can use it to check that a given XML document is valid and follows the rules you've laid out in the schema.
WSDL is a XML document that describes a web service. It shows which operations are available and how data should be structured to send to those operations.
WSDL documents have an associated XSD that show what is valid to put in a WSDL document.
XSD : XML Schema Definition.
XML : eXtensible Markup Language.
WSDL : Web Service Definition Language.
I am not going to answer in technical terms. I am aiming this explanation at beginners.
It is not easy to communicate between two different applications that are developed using two different technologies. For example, a company in Chicago might develop a web application using Java and another company in New York might develop an application in C# and when these two companies decided to share information then XML comes into picture. It helps to store and transport data between two different applications that are developed using different technologies. Note: It is not limited to a programming language, please do research on the information transportation between two different apps.
XSD is a schema definition. By that what I mean is, it is telling users to develop their XML in such a schema. Please see below images, and please watch closely with "load-on-startup" element and its type which is integer. In the XSD image you can see it is meant to be integer value for the "load-on-startup" and hence when user created his/her XML they passed an int value to that particular element. As a reminder, XSD is a schema and style whereas XML is a form to communicate with another application or system. One has to see XSD and create XML in such a way or else it won't communicate with another application or system which has been developed with a different technology. A company in Chicago provides a XSD template for a company in Texas to write or generate their XML in the given XSD format. If the company in Texas failed to adhere with those rules or schema mentioned in XSD then it is impossible to expect correct information from the company in Chicago. There is so much to do after the above said story, which an amateur or newbie have to know while coding for some thing like I said above. If you really want to know what happens later then it is better to sit with senior software engineers who actually developed web services. Next comes WSDL, please follow the images and try to figure out where the WSDL will fit in.
***************========Below is partial XML image ==========***************
***************========Below is partial XSD image ==========***************
***************========Below is the partial WSDL image =======*************
I had to create a sample WSDL for a web service called Book. Note, it is an XSD but you have to call it WSDL (Web Service Definition Language) because it is very specific for Web Services. The above WSDL (or in other words XSD) is created for a class called Book.java and it has created a SOAP service. How the SOAP web service created it is a different topic. One has to write a Java class and before executing it create as a web service the user has to make sure Axis2 API is installed and Tomcat to host web service is in place.
As a servicer (the one who allows others (clients) to access information or data from their systems ) actually gives the client (the one who needs to use servicer information or data) complete access to data through a Web Service, because no company on the earth willing to expose their Database for outsiders. Like my company, decided to give some information about products via Web Services, hence we had to create XSD template and pass-on to few of our clients who wants to work with us. They have to write some code to make complete use of the given XSD and make Web Service calls to fetch data from servicer and convert data returned into their suitable requirement and then display or publish data or information about the product on their website. A simple example would be FLIGHT Ticket booking. An airline will let third parties to use flight data on their site for ticket sales. But again there is much more to it, it is just not letting third party flight ticket agent to sell tickets, there will be synchronize and security in place. If there is no sync then there is 100 % chances more than 1 customer might buy same flight ticket from various sources.
I am hoping experts will contribute to my answer. It is really hard for newbie or novice to understand XML, XSD and then to work on Web Services.
XSD is to validate the document, and contains metadata about the XML whereas WSDL is to describe the webservice location and operations.
XSD (XML schema definition) defines the element in an XML document. It can be used to verify if the elements in the xml document adheres to the description in which the content is to be placed.
While wsdl is specific type of XML document which describes the web service. WSDL itself adheres to a XSD.
WSDL - It contains the Operation such as Methods which a webservice provides.and these method can accept simple data types such as int,float etc and complex data types such as objects ,vectors, arrays etc. so mapping this to an xml datatype xsd are used. and based upon the xsd an user who wants to acccess webservice from different platform can provide the data appropriately.
Refer : ayazroomy-java.blogspot.com to read about basics of webservice.
If someone is looking for analogy , this answer might be helpful.
WSDL is like 'SHOW TABLE STATUS' command in mysql. It defines all the elements(request type, response type, format of URL to hit request,etc.,) which should be part of XML. By definition I mean:
1) Names of request or response
2) What should be treated as input , what should be treated as output.
XSD is like DESCRIBE command in mysql. It tells what all variables and their types, a request and response contains.
XSD is schema for WSDL file. XSD contain datatypes for WSDL. Element declared in XSD is valid to use in WSDL file.
We can Check WSDL against XSD to check out web service WSDL is valid or not.
Related
When I'm tasked with dealing with connecting to web services, I've always found the appropriate .wsdl file, ran WSDL2Java.bat, and incorporated those Java files into my Java project. Then I've successfully completed my project that needs to access data via web services.
My question is, are there other ways to use the .wsdl file to access web services? ( I'm not talking about creating classes for different languages ). For example, I have documentation describing one company's web services. The examples it shows in it's documentation are essentially dumps of HTTP Post requests. Is this "web services"? It looks to me that the .wsdl file is merely used as a reference to make the correct Post requests. I could just make text templates and plug in the right values, and send them out, right? I really feel like I'm missing something here.
Am I a web-services illiterati?
To call a SOAP web service over HTTP you just need to send it a properly formatted XML with a POST request. That's it! How you build the request is irrelevant as long as it conforms to the SOAP protocol and the payload corresponds to a proper web service operation that exists on the particular web service you are calling.
But how do you know how to build the proper payload?
The web service needs to have some sort of documentation otherwise you don't know what to put inside the XML. The documentation can be whatever you like as long as people can use it to build valid requests. WSDL fits this criteria but has an extra advantage: you can feed it to a tool that generates code. That code knows how to handle all the SOAP details and exposes objects and methods to your application.
What would you prefer? Generating code from the WSDL in a few minutes and be able to call whatever operation on the web service or, build the requests and parse the responses by hand and spend hours or days doing so. What would your boss or company prefer? :)
It looks to me that the .wsdl file is merely used as a reference to make the correct Post requests. I could just make text templates and plug in the right values, and send them out, right?
Right! But you also have to consider your productivity as an employee in one case as opposed to the other.
We are developing an MDA platform that has support for Web Services. The user can provide a WSDL in runtime and we generate all the artifacts (service interface and implementation for the server, and consumer for the client) using JAX-WS internally.
We want to add validation on the WSDL document provided by the user. Right now the user has to validate that with an external tool like Oxygen, XMLSpy or a web tool, but we want to add that as a part of our system. A nice-to-have feature would be schema validation aswell, including the embedded schemas of the WSDLs.
In JAX-WS (RI) there is support for schema validation in runtime (using the #SchemaValidation annotation) but we haven't found any support for WSDL validation.
We've tried to integrate Eclipse's WSDL validator but it doesn't seem to work for us.
Is there any way of doing this with JAX-WS?
If not, is there any other validation framework that we can integrate?
Thanks
There is a bit of confusion in your question that I need to clarify first.
You seem to want the ability to validate the WSDL (syntax + WS-I) and XSDs, either embedded or referenced externally by the WSDL. On the other hand you bring in #SchemaValidation, which is actually used to validate instance documents.
In a traditional development approach, one might say you want at least the ability to validate design-time artifacts (WSDL+XSDs).
For this scenario then, I would recommend the following:
WSDL: for WS-I compliance testing, please take a look at the test tools section of the WS-I site. It is not clear how the licensing they have with their test tooling would work with yours, but at least it should give you an idea for what to look if it doesn't work for you.
UPDATE: Additional WSDL validation resources:
- Eclipse based, how to use outside Eclipse.
XSDs: if you really need separate validation for XSD files, things may get tricky for a production quality product; WSDL4J is not much help here, and I believe XSOM is the way to go for this kind of job. You have to extract content from the types section as one or more XSD files (could be more than one XSD file, take a look at some examples, Microsoft's SharePoint WSDLs come to my mind as a good test case), assign a base uri for each extracted XSD that matches the WSDLs location, then use XSOM to validate those.
Since you're generating the client, you're most likely not concerned with validating, say of the HTTP headers (SOAP 1.1/HTTP, SOAPAction, if it matches the WSDL operation definition). If you end up developing an interest in that as well, which I call runtime validation, then I would recommend a different layout in your approach (i.e. I would not rely on #SchemaValidation but rather do it through a transparent, and generic, proxy service).
I am consuming a web service into my application. Now I have been informed that there will few changes in the web services but all methods(i.e. output from web service) exposed form the web service will not change.
I have got the WSDL link for both old and new webservices. Now, I want to compare the old and new webservice so that I can be sure that we are not missing any data.
Could anyone help me on the same i.e how to compare the two WSDLs?
The WSDL documents should have a "types" element with nested XMLSchema (e.g. <xsd:schema>) elements which may include import statements or inline XML schema definitions.
Compare the structure of the elements which are used as part of any "message" to see if there are any changes to their XML structure.
I used WCF to create a restful web service in .NET, by means of a .svc file. The web application automatically produces a WSDL file. AFAIK, the WADL is more natural for a restful web service.
How could I create a restful service in .NET (preferably with wcf) that produces a WADL description?
Note An answer like "RTFM" is accepted, as long as you indicate a suitable manual/tutorial.
This is an old question but having consumed restful services with WADLs they do offer some value. You can import them straight into SOAPUI and it will build a test suite for you automatically. Secondly they tend to contains all the required XSDs for XML based services and are useful for automatically building serialisable classes that your endpoints accept and receive.
Looks like REST Describe & Compile should do the trick.
On the WADL developer site Marc Hadley
maintains a command line tool named
WADL2Java. The ambitious goal of REST
Describe & Compile is to provide sort
of WADL2Anything. So what REST
Describe & Compile does is that it:
Generates new WADL files in a completely interactive way.
Lets you upload and edit existing WADL files.
Allows you to compile WADL files to source code in various programming
languages.
Forgive me for answering a question with a question, but do you really want to do REST? REST really has no need for things like WADL.
Update:
The "hypermedia constraint" (aka HATEOAS) dictates that the user agent discovers content based on links embedded in previously retrieved content. It really is unnecessary to have a separate document that describes all the available content.
Imagine using a web browser to go to a site and instead of going to the home page and navigating from there, you are presented with a page which is a list of all the URLs on the site. You must then looks through the list of available urls, choose the one you are interested in and copy it into the address bar.
WADL is effectively you list of site urls. You just don't need it if your main content is linked together.
Linking content instead of using a WADL "site map" has other advantages. The available links can be dynamic based on particular data values in the content. This capability can vastly reduce the complexity of clients, because the client no longer needs to host the logic to decide when it is allowed to follow a link.
In an answer to another question it was mentioned that passing XML as a string parameter to a web service was bad practice. What is the reason for this?
This question is at least in part due to a comment of mine about string parameters containing XML being bad practice in web service design. Here's why:
If the web service author wanted his service to accept XML, with or without a schema, then he should have defined the parameter as being of the XML Schema type <xs:any/>. That permits an arbitrary XML element. It's possible to restrict the permitted XML by using <xs:any namespace="xml namespace" processContents="strict" />. This will restrict the XML to being from the particular namespace, and will validate the XML against schemas. The recipient of such a message will be able to process it as pure XML, or possibly as type object or XmlElement or the platform equivalent.
In contrast, if XML is passed as a string, then the recipient has to take action to turn it back into XML. This assumes that actual XML has been properly encoded into the string.
Passing a string also loses you the benefits of XML. For example, the encoded XML cannot be easily processed by XML-based tools, such as XSLT.
I have used many web services that take simple XML values as a parameter or return them as output, so I am not sure exactly why someone would consider it to be a bad practice, but I could describe a few of the weaknesses.
The main downside that I can see to using arbitrary XML as an input parameter is that by itself it does not provide strong typing. If you are using a SOAP based web services with a WSDL that outlines the web service input and output variables then using basic XML as a variable does not give the user very much information. This is especially the case if you have a basic string input value to which you assume the user will enter XML data. A better approach is to use an XMLElement or XMLNode type instead of a standard string, so that there is at least a basic level of type checking for valid XML in the web service. The idea with SOAP and WSDL though are to create strongly typed parameters so that full objects can be passed back and forth across the wire between applications. You basically can create an object and use that as the basis for your input or output values and SOAP will handle the creation of a schema for serialization and de-serialization for you automatically.
The problem is that using complex data types can significantly increase the complexity required for calling the web service. Web services are offered in a variety of flavors from simple REST services to a complex web of WS - * protocols for strongly typed messages. Using Plain Old XML with no schema would definitely be a bad idea if you are building a Business to Business web service based on WS - *, but if you are creating a simple REST service then POX might suit your needs just fine.
Its bad practice because it opens your web server to potential injection or XSS or URI poisoning types of attacks. Most web servers are never updated or patched even when they are identified as vulnerable to attacks.