The intention is to build a intra-network semantic web services, but struggling to get the concepts together. Please care to answer the following questions:
We annotate ontologies to WSDL elements in SAWSDL, but where does the web server store the reference ontology file for the benefit of client?
Is it mandatory to describe the pre-conditions and effects of atomic/simple processes? If yes, why?
As per W3C specifications, unlike SAWSDL, OWL-S decouples the ontology and WSDL files. WSDL, which is completely decoupled from semantics, is used only at the time of service invocation. If that is the case, how does client find ontology information during service discovery phase?
In SAWSDL, concepts are identified by URIs in the form of attribute values of the modelReference attribute.
Related
Is REST the future for SOA:
SOA architectural style is based on a functional decomposition of
enterprise business architecture and introduces two high-level
abstractions: enterprise business services and business processes...
REST, on another hand, is a set of architectural guidelines expressed
as Resource-Oriented Architecture (ROA). ROA is based upon the concept of resources;
... it is impossible to build an SOA system using true REST.
and
The REST Web Service approach is an approach for using REST purely as
a communication technology to build SOA. In this case, services are
defined using SOA style decomposition and REST-based Web Services
are leveraged as a transport.
Could you pls explain in more details the last quote? Did they mean RESTful Web Services is smth different from REST or not only a REST or what? What did they mean by use REST as a communication technology? What did they mean by "REST-based Web Services are leveraged as a transport"?
Update: for tonicsoft answer
Due you can't build SOA with pure REST (like sentence with pure nouns) I'm wondering what is the right way of arranging app parts where REST is appropriate and where isn't? Should I separate REST-part from not-REST parts? How not-REST part should comunicate among each other and with REST parts?
Yes, the article is stating that REST is something different to "RESTful web services".
The author compares REST to "nouns" as opposed to verbs, or the "DBMS" of the web. Can I write a sentence without using verbs? No. Can I build a system using only a DBMS? No. In the same way, one cannot build a system only using REST architecture principles. In most systems REST semantics break down eventually. One example given in the article is when a messaging solution is required.
I think the author is saying the a "RESTful web service" is the whole sentence whereas REST is just the nouns. In a "RESTful web service", the parts of the system which do not have REST semantics (basically anything that is not CRUD) can be implemented using similar technologies and programming styles often found in the implementation of pure REST components.
"REST as a communications technology" basically just means restricting the transport implementation of the service to HTTP. Most web services frameworks provide multiple options for the transport (e.g. WCF can do SOAP over HTTP, or use shared memory, or TCP for networked services without HTTP). REST shuns this flexibility in favour of simplicity. A "RESTful web service" will be purely HTTP based, according to my interpretation of the quoted article.
In summary, REST is simply an architectural style. It is impossible to build any technology solution of note using only one architectural style. Therefore a "RESTful web service" is simple a web service that leverages the REST architectural principles where appropriate.
Again, this is not my opinion, it is simply my interpretation of what the article is saying.
How to seperate pure REST operations from the rest of your "RESTful web service"
I don't think any particular seperation is needed between the pure "REST" endpoints (CRUD) and the more behavioural/service oriented endpoints, beyond the fact that any given URL should be either one or the other, and you may find that you don't want to mix the two styles under the same base URL. For example, if you have a REST endpoint for retrieving the details of a user account with id=1234:
/users/id/1234
and you want to implement a "verify email" workflow (which for argument's sake is not implemented as a REST service), then choose a URL for your verify email workflow/service that doesn't clash with the REST style /users/ API. Don't be tempted to do things like this:
/users/id/1234/verifyEmail?securityToken=XXXX
but instead, prefer to create a completely new URL for this endpoint:
/verifyEmail/userId/1234?securityToken=XXX
These guidelines are largely arbitrary: the important thing is to design your service in a way that will make sense other programmers, as these are the people who will use your service. As with any other bit of software design, Single Responsibility Principal will get you a long way. Each base URL should only do one thing!
As mentioned in th e introduction, the H ypermedia as the E
ngine of A pplication S tate (HATEOAS) constraint is one of
the least understood constraints, and thus seldom implemented
correctly. Annoyed by the fact that a lot of services claim
to be RESTful regardless of violating the hypermedia
constraint, Fielding [29] made it very clear that hypermedia is
a fundamental requirement but since the term REST is so widely
misused, there are e fforts in the community to look for an
alternative term, such as Hypermedia API , to denote truly
RESTful services
http://www.ws-rest.org/2012/proc/a4-2-lanthaler.pdf
http://www.markus-lanthaler.com/research/third-generation-web-apis-bridging-the-gap-between-rest-and-linked-data.pdf
http://roy.gbiv.com/untangled/2008/rest-apis-must-be-hypertext-driven
The REST architecture has well defined constraints you can find here: http://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm
The term RESTful comes from the Richardson Maturity Model as far as I know. http://martinfowler.com/articles/richardsonMaturityModel.html I don't know where the original article is, but as far as I know it is some nonsense, something like you should call every API REST, which fulfills at least a single constraint and you should call RESTful only those APIs which fulfill every REST constraint. Fielding made clear many times that only APIs which fulfill all constraints are considered REST and APIs which don't are simple web APIs, but not REST APIs. Sadly both REST and RESTful words are overused by developers who know nothing about REST. Most of them don't even know that REST constraints exists. For them REST is only CRUD and URI design. Just check SO questions about REST, 99% is that kind of stuff. Even funnier that I get minus points from them when I answer questions related to REST... So to avoid confusion and misunderstandings we build Hypermedia APIs now, so we can live in piece as long as people do not start to use this word as well...
I cannot make sense from most of the questions. I compared REST and SOAP here along with many people Representational state transfer (REST) and Simple Object Access Protocol (SOAP) maybe you find an answer to your questions.
How not-REST part should comunicate among each other and with REST
parts?
If you mean microservices by app parts, then ofc. SOA and REST microservices can communicate with each-other simply by sending HTTP and SOAP messages to each-other. If you don't have a legacy SOAP system, then I recommend to develop only REST services, since SOAP is stateful, and so it does not scale as well as REST.
I am currently dealing with semantic descriptions of web services, OWL-S more specifically. I'm not manually writing the annotations, I use this tool.
My point is not the annotations per se, but to know how close 2 web services are. So my idea was to try and compare their respective OWL-S descriptions.
What I'm looking for is maybe a matcher, an API (Java or Python) that would allow me to match two .owl files.
UPDATE : This is just my idea. If you can suggest something else that serves the same purpose you are welcome.
You could try LogMap, it's a framework for ontology matching. You can try it from the web interface. In case of problem you can contact directly the authors of the tool too.
I understand that you can describe your REST webservice while using WSDL.
Is this a good idea if you don't use WCF? Is there a better way to allow service discovery and bind your request/response to certain types?
If you use json you can use SMD and JSON-Schema but what if you use XML or YAML?
EDIT:
I have found this specification for WADL.
How widely used is it?
The Http Accept header and Content Type headers are there to allow a client to dynamically request and respond to different types. Statically describing what those types are in some kind of description file like WSDL would be unnecessarily limiting.
The use of hyperlinks within the returned representations allows for incremental service discovery. This allows the service discovery to be dynamic based on a whole range of factors.
The use of a global static service discovery document like WSDL or WADL is really not the optimum solution with a REST service.
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.
I am little bit confused about what really a web service is. You say Amazone web services,etc like that, they offer information. So what is the requirement to be a web url to be a web service ? Let's say I am not much familiar with web development, how could you explain it to me ? But I can get it if you point some ways.
And also little about SOAP and REST basically for someone really new
What is a web service
It is many things. In programming, in generally refers to a web page, that can be called from an application (be it another web page, or desktop app), and the caller will pass in data to it, or receive data from it.
In this sense, it's basically like a 'method' or 'function' in a normal programming language; except you're calling it over the internet.
SOAP
A message format. As discussed above, a web service is a basically a 'method' or 'function'. SOAP is the 'instructions' and 'data' to this method. It will outline data types, and possibly a bunch of data as well. It is an XML format.
REST
REST is the means of implementing an interface to your application but, implementing access control, and other such things, specifically with HTTP Response codes. So you will get a 401: Denied (I think that's the right code), if you don't have access. There are other types of response codes that are useful. It also makes use of other HTTP commands like PUT/HEAD/OPTIONS.
The W3C defines a Web Service as (quoting) :
A Web service is a software system
designed to support interoperable
machine-to-machine interaction over a
network. It has an interface described
in a machine-processable format
(specifically WSDL). Other systems
interact with the Web service in a
manner prescribed by its description
using SOAP-messages, typically
conveyed using HTTP with an XML
serialization in conjunction with
other Web-related standards.
That definition is maybe a bit too restrictive, considering how that term is used nowadays -- I'd probably go with just the first part of that definition, which is quite generalist :
A Web service is a software system
designed to support interoperable
machine-to-machine interaction over a
network.
Wikipedia also has some interesting definitions, like :
In common usage the term refers to
clients and servers that communicate
over the Hypertext Transfer Protocol
(HTTP) protocol used on the Web.
From what I've seen :
A couple of years ago, when we said "web service", we generally meant "SOAP, WSDL, ..."
Now, when we say "web service", we often mean "whatever allows to call something on another server, be it SOAP, REST, ..."
A Web-Service can be considered as a set of methods that enables communication amongst applications irrespective of the application's coding language or framework.
http://acharyashri.com/blog/WebServices.html
Think of Web services as remote APIs (since they are basically just that). You have a method that you want to implement. Let's suppose the method wasn't built by you and resides somewhere else in the world on equipment that you have no control over—how can you go about providing that remote method what it needs in order to get instantiated?
When you find a Web service that you want to include in your application, you must first figure out how to supply the Web service with the parameters it needs in order for it to work. That need also extends a bit further. Even if you know the parameters and types that are required for instantiation, you also need to understand the types that are passed to your application in return. Without these pieces of information, using Web services would prove rather difficult.
Just as there are standard ways to represent data as well as standard ways to move this data over the Internet using Web services, there is a standard way to get a description of the Web service you are interested in consuming. Web Services Description Language (WSDL) is a specification of XML that describes the Web services you are interested in consuming. It's just an interface to describe a web service.