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70-562 Web Services


A single server can't handle it all, connecting many computers together is far more powerfull than in a mainframe.

In distributed applications, One cluster may be for the database, then a group of servers might function as a specialized application server, and still others handle user interface and security logic.
All those computers need to communicate together.

There are 4 broad WS technollgies,
1) Universal access: The tcp/ip is most common protocol
2) Standard data representation: xml is intended to transport data. And XPath that allows to xtract a subset of data easily, while http was made for to transport markup(html). While
3) Standard message format: SOAP stadardizes the message envelope
4) Service description format: WSDL web services description language

The web service has to derive from System.Webh.Services.WEbService and contain the WebSErvice and WebSErviceBinding attribute.
The WebMethod attribute is added to each methods exposed to the outside world.
The http://tempuri.org is a placeholder, you can put one of your own, there is not repository keeping track of it, it doesn't need to be browsable, it's just an id to uniquely identify like a guid would do.
Must be constant over time: versioning.
Use datasets or custom objects(serialized).
Chunky is better than chatty, sending a big chunk of SOAP is better than a bunch of little chunks.

The client has to capture the types and web methods, this is done by adding a service reference to the client project, this is when the wsdl file is generated.
Visual Studio creates a proxy class that will handle the request and response.

The disco file contains the location of the wsdl file, the client uses this file, the discomap maps both wsdl and disco file togther.

WCF: Contract is a key concept, the client and the server agree wont change.
DataContract is used to identify types.
ServiceContract defines the service, usualy defined as an interface.
The svc file provides the service host, in a command line application this one would need to be created manualy. To test the service availability, invoke this svc file in the browser.
WCF is a topic in it's own, this just scratch the surface, but is all that is needed as far as 70-562 goes.

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