For SOAP web services there is a specification which all request/responses must follow. This specification is in the form of a WSDL document. However for REST web services, why is there no such specification or WSDL? Does this make REST more vulnerable to runtime exceptions because we are not following any specifications?
There are bunch of ways to define a RESTful API just like WSDL for SOAP:
Google Discovery service format.
Mashery IODocs.
WADL.
Swagger.
Apiary.
You can find more info here on my blog post.
REST really only uses the HTTP verbs (GET, PUT, POST, DELETE, …) on a resource. All operations on a resource are supposed to be represented that way. POST is used as a catch all for when you can't express your business logic in a way that fits into the other three. That is why there isn't really a WSDL for a REST service since you only ever have 4 methods on the resource.
But you still have the possibility to describe a REST web service with WSDL 2.0.
SOAP is a protocol.
REST is an architecture.
In many references you will see REST and SOAP both mentioned as
competitors. That is not true. SOAP is actually a protocol, not an
architecture style. What REST can be compared against is SOA and RPC.
All three are examples of web service styles, each with their own
conceptual focus. RPC is focused around operations, SOA around
messages, and REST around resources. (ref)
So for SOAP, wrote WSDL document standards. But for REST there is not a standard document, but there is many the best practices be like http://jsonapi.org
Related
We are using SOAP based web services to let end user schedule service appointments. Our portal is WebService client & we have a number of Vendors(who are spread across the globe in various timezones) who are building Webservice Server operations.
We are thinking to build it as a contract first SOAP based web services so that we have tight control(interface based e.g. date-time format should be standard xsd:dateTime etc.) over what can be sent & received as part of XML messages for possible success & error scenarios(via different error codes). We want to keep single client code for all the vendors. We would like to determine
1) Should we think about using RESTful web services?
2) Is there any way the vendors can use RESTful services also if they want at their end(by sticking to our WSDL contract) & we use SOAP at our end
First a little bit about,
REST (Representation State Transfer) is an architecture style to develop webservice. In which data and functionality are considered as a resource and can be accessed via URI (Uniform Resource Indicator). It follows client server architecture and uses stateless protocol (usually HTTP). Typically in REST webserivces resources are acted upon by GET, PUT, POST,DELETE operation. Generally we use JSON to exchange data between client and server. It is light weight.
On the other hand SOAP (Simple Object Access Protocol) is a XML based mesaage protocol. Which is generally used on enterprise level to define their own interfacing and operations as services. It also follows REST architecture.
So basically, it is a RESTful webservice.
Now to answer your question,
It seems you are going to expose your webservice client on enterprise level. Which is going to be used by many vendors to implement their own webservice server.
So, it is perfect, you go with SOAP webservices.
You will define the skeleton of the webservice like Message formats, Operations, binding etc which is called WSDL. It is widely used standard and very easy to understand by any third party. Something called WADL is used for REST services also but it is not very user friendly.
The same contract (WSDL) will be used by your vendors to implement the webservice on their server in Top to Bottom approach using some API, for example JAX-WS.
This way you will have a tighter control over your operations, formats, security etc. in a single contract (WSDL).
Now if a vendor wants to use REST webservice instead of SOAP. You can build a JAVA proxy on top of your client. Which will convert your soap messages into REST to send/receive request/response to REST webservices. But you can not dictate your contract in this approach. Although, You can recommend vendors to build their own proxy to handle your SOAP webservice requests. This way your contract will be intact.
If you are going to expose your webservice client for small applications then it is alright to go with REST but if you are an enterprise and going to expand in future, you should go with SOAP for robust features and easy maintenance.
Disclaimer: please do not consider this answer as really serious.
Well, I think question too abstract. Why do you asking it? Because you see yourself that currently everything is RESTful? Then you'r right. You can do any protocol. But if you will do REST with JSON instead of XML, everybody will thank you. And if you will use 40 years old technology for creating modern service, then probably not. Same for your contractors.
The only advantage SOAP seems to have in your situation is that it is already implemented.
SOAP is a complex standard with unfriendly implementation and verbose implementation - i.e. hard to work with and maintain. Also note that you are not even using it "by the book" since your security is external to it and not using ws-security
REST based interfaces would make your and your users' lives easier. I suggest you take a look at standards and tools like swagger for building APIs.If you're running on premise you can take a look at API gateways like tyk If you're running in the cloud you also take a look at AWS API Gateway
Does a RESTful web service (e.g. in a JAX-RS implementation) support both contract-first (top-down) approach and contract-last (bottom-up) approach?
Do RESTful web services support both contract-first and contract-last approaches?
It depends on what tools/frameworks you use.
What you are talking about applies to a SOAP web service and its accompanying WSDL.
A WSDL describes what a web service expects as input and what should a client expect as output. It defines the contract to be followed in order for both parties to communicate with each other. You can obtain the WSDL by doing contract-first or contract-last and you can later use this WSDL to generate code for a client stub or a service skeleton.
But doing REST isn't the same as doing SOAP. Processes that worked for SOAP (a protocol) can't necessarily be applied to REST (an architectural style) just because we are familiar with them.
Unlike SOAP that exposes methods and method signatures, REST exposes resources. An understanding of the media types used in the exchange of those resources is all a REST client needs in order to communicate with a REST web service. There is no need for a separate document to describe the resources.
Because of the HATEOAS principle, REST clients are more dynamic and can adapt to other services that communicate using the same media types. Exposing static service description documents would be limiting for a REST service.
Having said that, there are REST tools that do expose a description document, for example Jersey who exposes a WADL (contract-last). I'm sure you can use the published WADL to build client stubs and I don't see a reason why you couldn't write the WADL by hand (contract-first) and use it to generate stubs and skeletons. But as I said, that might not be the best solution for REST.
Here are some posts you might want to read to form an opinion if contract-last or contract-first approaches make sense in REST:
Does REST Need a Description Language?
Why the slow WADL uptake?
There are 2 types of web-services as I know. First one is custom xml formatted messages and the second one SOAP standard xml messages. What are the differences between them? Which one is better, what are pros and cons of each of that two approaches?
By "ordinary" I assume you mean RESTful services. This discussion would be a long one, so I'll try to give you some key points:
RESTful services are the most used flavor of Web Services. They are closely linked to the functionality and principles of HTTP and can be accessed as simple as a GET request (other operations are POST, DELETE and PUT). The core concept is the "resource" which is identified by an URI. Common formats for REST are XML and JSON. It's a pretty straightforward and easy to use technology, which is what makes it so widely available.
SOAP web services are based on XML, most of them adhering to the RPC-style of app design (calling remote methods on a server and getting a response), and use 3 main pillars:
WSDL - Web Service Description Language - used to describe a service in terms of available operations, parameters, etc.
SOAP - Simple Object Access Protocol - used to construct interaction messages between the entities involved (client, server).
UDDI - Universal Description, Discovery and Integration - used to classify and publish available web services to a repository and enable discovery by potential users.
SOAP Web Services tend to have high overhead and generally have very verbose messages, but may be good if you need to implement more complex functionality and interaction in your application.
Strictly speaking only the Soap services are webservices. They are based on the WS-* Specs standardisized by W3C and Oasis. Sometimes a also reffered as Webservice are so called POX-Endpoint (Plain old XML) or REST Endpoint, which allows you to simply get a raw XML via HTTP GET.
SOAP Services carry their schema in form of a wsdl endpoint (usualy append ?wsdl to the service endpoint), so there a lots of tools to create proxy objects and hide the complexity of the webservice call. With POX Services you need to know which schema to use from e.g. the documentation.
SOAP Services carry the payload inside the SOAP Envelope (an XML Schema with header and body with the payload in the body). Having a header independent from the payload allows to reroute the content, sign and encrypt, authenticate etc. without knowing the content. But you pay by additional overhead in the message itself.
POX on the other hand leaves all that to the webserver and relies usualy on HTTP for authentification and compression. Encription and signing had to be done by your system. It is low overhead but also low discoverability.
Whats works best for you depends a lot on your scenario. If you work in a .Net or Java World, you often find it simplest to create a proxy and use that to work with the webservices as remote objects. You get a well build infrastructure and a comfortable programming experience. If youre environment does not support the proxy generation or if it had to be called from anything, POX might the very much more lightweight way to go.
"Web Service" refers to a more abstract and general concept. We can say that anything that can be served on web is a Web Service. SOAP Web Services or RESTful services are special kind of Web Services which has wide acceptance and has their own standards. While SOAP services are built on a new XML based standard, RESTful approach makes use of existing HTTP methods, hence more widely accepted (to my experience).
I am new to the arena of RESTful services. I have been going through the articles about REST. And I have a lots of doubts. Please help me to clear these doubts. Thanks in advance.
1) For all RESTful web services, will there be a WSDL/WADL for describing the service? Is it mandatory to have service description? If there is no description, how can I know the data and its structure that I have to send along the HTTPRequest?
I read like, the request content could be any type (XML, JSON, YAML etc.). And there is no restriction for the content-type that could be send with request. Without a description how can I know the type of data that I am supposed to send?
2) By going through the articles, I have got the impression that RESTful services is used mainly for CRUD operation kind of services. Different HTTP verbs for different operations. But if you take web services, it can do all kinds of operations. For example, adding 2 numbers is not exactly a CRUD operation. If I use GET/POST to the resource which could do this operations for me, then will it be a violation of REST principles?
3) If you can point me to any public RESTful webservices that could be used for testing, I could try using the service and get an idea how complex the services could be.
Thanks in advance,
Paul
There is normally no machine-readable service description. You would typically know what to send by reading the documentation for the service.
REST isn't limited to CRUD and the PUT/GET/POST/DELETE methods are not necessarily the same as create/retrieve/update/delete. REST-based services can do anything that SOAP-based web services can do. It is completely RESTful to send a GET request to a URI like http://example.com/add?3,5.
You can find a list of REST services at http://www.programmableweb.com/apis/directory/1?protocol=REST.
Answer to your first question :
WSDL/WADL is not mandatory for restful webservices. Also, WSDL 1.1 HTTP binding was inadequate to describe restful webservice.
However, WSDL 2.0 can be used to describe it. Restful webservice should be used when the client and provider have mutual understanding of the contract.
Have a look at : http://www.ibm.com/developerworks/webservices/library/ws-restwsdl/
Second : Yeah, you can accomplish almost everything from crud operations. Like stated in previous answer http://example.com/add?3,5. is a valid crud.
No WSDL/WADL files. You get the HTTP protocol (e.g. GET, POST, UPDATE, DELETE) and everything else is up to you. Make sure to document your expected inputs and outputs accordingly.
No, RESTful web services are not restricted to CRUD. For your adding service, I would implement it as an "adder" resource which would take as input the 2 numbers to add. You could take these inputs as part of the url path (http://yourdomain.com/adder/1/2) or in the query string params (http://yourdomain.com/adder?var1=2&var2=2) or as inputs from an HTTP POST. Up to you.
What is the difference between OData and REST-ful web services?
UPDATE Warning, this answer is extremely out of date now that OData V4 is available.
I wrote a post on the subject a while ago here.
As Franci said, OData is based on Atom Pub. However, they have layered some functionality on top and unfortunately have ignored some of the REST constraints in the process.
The querying capability of an OData service requires you to construct URIs based on information that is not available, or linked to in the response. It is what REST people call out-of-band information and introduces hidden coupling between the client and server.
The other coupling that is introduced is through the use of EDMX metadata to define the properties contained in the entry content. This metadata can be discovered at a fixed endpoint called $metadata. Again, the client needs to know this in advance, it cannot be discovered.
Unfortunately, Microsoft did not see fit to create media types to describe these key pieces of data, so any OData client has to make a bunch of assumptions about the service that it is talking to and the data it is receiving.
The OData protocol is built on top of the AtomPub protocol. The AtomPub protocol is one of the best examples of REST API design. So, in a sense you are right - the OData is just another REST API and each OData implementation is a REST-ful web service.
The difference is that OData is a specific protocol; REST is architecture style and design pattern.
REST is a generic design technique used to describe how a web service can be accessed. Using REST you can make http requests to get data. If you try it in your browser it would be just like going to a website except instead of returning a web page you would get back XML. Some services will also return data in JSON format which is easier to use with Javascript.
OData is a specific technology that exposes data through REST.
If you want to sum it up real quick, think of it as:
REST - design pattern
OData - enabling technology
In 2012 OData underwent standardization, so I'll just add an update here..
First the definitions:
REST - is an architecture of how to send messages over HTTP.
OData V4- is a specific implementation of REST, really defines the content of the messages in different formats (currently I think is AtomPub and JSON). ODataV4 follows rest principles.
For example, asp.net people will mostly use WebApi controller to serialize/deserialize objects into JSON and have javascript do something with it. The point of Odata is being able to query directly from the URL with
out-of-the-box options.
From the OData documentation:
The OData Protocol is an application-level protocol for interacting with data via RESTful web services.
...
The OData Protocol is different from other REST-based web service approaches in that it provides a uniform way to describe both the data and the data model.
OData (Open Data Protocol) is an OASIS standard that defines the best
practice for building and consuming RESTful APIs. OData helps you
focus on your business logic while building RESTful APIs without
having to worry about the approaches to define request and response
headers, status codes, HTTP methods, URL conventions, media types,
payload formats and query options etc. OData also guides you about
tracking changes, defining functions/actions for reusable procedures
and sending asynchronous/batch requests etc. Additionally, OData
provides facility for extension to fulfil any custom needs of your
RESTful APIs.
OData RESTful APIs are easy to consume. The OData metadata, a
machine-readable description of the data model of the APIs, enables
the creation of powerful generic client proxies and tools. Some of
them can help you interact with OData even without knowing anything
about the protocol. The following 6 steps demonstrate 6 interesting
scenarios of OData consumption across different programming platforms.
But if you are a non-developer and would like to simply play with
OData, XOData is the best start for you.
for more details at http://www.odata.org/
ODATA is a special kind of REST where we can query data uniformly from URL.
REST stands for REpresentational State Transfer which is a resource based architectural style. Resource based means that data and functionalities are considered as resources.
OData is a web based protocol that defines a set of best practices for building and consuming RESTful web services. OData is a way to create RESTful web services thus an implementation of REST.