>The advantage of generating a
WSDL file is that each client can download the WSDL file and generate
proxy "on the fly".
But what proxy classes do, the same can be done using business objects.
In other words, the logic that a proxy class encapsulates, the same
logic can be implemented using a business object i.e. both of them can
be used to retrieve data dynamically but using WSDL means the client
has to save the proxy file (along with the disco & results.discomap
files though not necessarily) in his machine thus consuming disk space
but with business objects, the client needn't save anything on his hard
disk.
Moreover to access the methods & properties in a proxy file, the client
has to pass commands to the Web Service (which maybe preceded by first
finding where the Web Service exists using DISCO) but with business
objects, there isn't any need for clients to use any extra tools like
WSDL.exe & DISCO.exe to access the business object's methods &
properties.
Both Web Services & business objects require compiled objects that are
implemented in ASP.NET pages. An ASP.NET book for beginners states that
the ONLY difference between Web Services & business objects is that
with Web Services, the compiled object (i.e. the proxy class) can
reside anywhere on the Internet. In other words, the ASP.NET page can
be located on a client's home computer in New York while the Web
Service resides on a server which is in Tokyo. But even business
objects that reside on a server in Tokyo can be accessed by an ASP.NET
page which is located in a client's machine in New York!
So what's the difference between Web Services & business objects or
what are the advantages of using Web Services (using WSDLs & sometimes
DISCOs) over business objects?
Thanks,
Regards,
Arpan
Laurent Bugnion wrote:
Hi,
Arpan wrote:
Web Services make use of proxy classes whose methods & properties are
accessed in exactly the same way as how a normal class' methods &
properties are accessed. So what for does ASP.NET generate proxy
classes (using WSDL) which consume more hard disk space & resources?
<code snipped>
The above code spans just 11 lines but if the above code (excluding the
2 Namespace lines) is encapsulated in an ASMX file after which WSDL is
used to generate a corresponding class file, the class file spans
almost 100 lines (excluding the commented lines). Moreover, most part
of the code in the generated class is not comprehensible to newbies
like me. So why use WSDL to generate a class file? Also there
definitely must be some additional overheads involved in this approach,
isn't it?
Thanks,
Arpan
WSDL is Web Service Description Language. It is a standard which is used
to describe what the Web Service can do. The advantage of generating a
WSDL file is that each client can download the WSDL file and generate
proxy "on the fly". This is what Visual Studio does when you create a
WebReference to a web service, and it generates proxies. However, there
are also other consumers of web services (ATLAS in JavaScript), and they
also create proxies in JavaScript dynamically using the WSDL file. Since
JavaScript is a very different language than C# and VB.NET, and since
web services may actually be written in yet other languages, WSDL
abstracts the language differences and allows different languages to
communicate through this medium.
It's very possible to do AJAX without SOAP and without WSDL. The code is
much thinner then. But SOAP and WSDL offer an additional level of
comfort for the consumer of web services.
.NET creates WSDL files automatically (just use the URL
myService.asmx?WSDL), but other providers of web services (Google comes
in mind) also deliver WSDL files with their web services.
HTH,
Laurent
--
Laurent Bugnion, GalaSoft
Software engineering: http://www.galasoft-LB.ch
Private/Malaysia: http://mypage.bluewin.ch/lbugnion
Support children in Calcutta: http://www.calcutta-espoir.ch
