Web Server Administration

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3 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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Web Server Administration

Web Services

XML

SOAP

Overview


What are web services and what do they do?


What is XML?


What is SOAP?


How are they all connected?


Web Services: What are they?


A
Web Service

is a software system that allows
services to be accessed over a network, and
executed on a remote system hosting the requested
services.


HTML transported over HTTP and presented via a
web browser is the most successful implementation
of remote access to a service running on another
machine.


The key is a
simple
,
accessible

message format,
that allows an application to be used by people all
over the world without installing custom client
software on their computers.


Web Services Continued


It’s an open standard, unlike prior standards such as DCOM,
CORBA, Java Remote Method Invocation (RMI).


APPS could be written using DCOM and if you are only dealing
with another PC using DCOM it works...if the DCOM port 135 is
open.


However, if the other machine is using CORBA or if you don’t
know what it ‘s using then open standard of web services is the
solution.


Everyone is offering web services tool kits! Java has one,
ASP.NET has one, and so do other languages and
environments.


It's probably one of the first times that all big players have come
to an agreement on a standard.


Web Services and XML


Web Services communicate with one another
via messages in a format known as
XML
.


Web services exchange XML messages with
one another, typically using either HTTP or
SMTP (e
-
mail) to transport the messages.


These Ports are usually open.



XML documents can be easily transported
via HTTP through firewalls without security
risks


“Valid” Web Services



The current web services standard, as defined by the W3C org, is composed of
4 main parts.



The service

which is usually performed by a web server that listens for requests
of the service. This is generally just a web like page or cgi script that gets posted
to similar to the way other HTTP web requests are done. Instead of returning
HTML though it returns a formalized XML message in Simple Object Application
Protocol (SOAP) format.



The service description

-

specified in Web Services Description Language
(WSDL)
-

this description defines the web methods (functions) that a service will
accept
-

the inputs that go into these methods, and the format of the output that
can be expected in return. It is the contract or message signature of the service.
This is what you will need to generate a web service client proxy. The .NET
Developer’s Kit comes with a utility WSDL.exe that will auto generate a client
proxy class in .vb or C# given a .wsdl file.



The web service registry
This piece is basically a directory of web
services. The current standard is Universal Description, Discovery, and
Integration (UDDI). This is an optional piece because a web service need
not be listed in a UDDI registry to be used. The registry is just a nice way of
cataloging available services
-

similar to what Java Naming and Directory
Service (JNDI) does for Java.



Finally there is the web service client proxy
-

which negotiates the
communication between a web service and a client. It accepts the inputs
and requests
-

passes it off to the web service
-

waits for the service to
respond and then converts the response to something meaningful. This is
known as serialization/deserialization
-

conversion from the web service
XML response back to an object and conversion of a user request to XML
format required by the service.


True or False?



Most corporate firewalls leave only port 80 open.

Answer
-

True


Web Services require DCOM for remote application
access.


False Web Services call remote applications using
XML in Soap syntax.


The service description

of a web service is an
optional component that defines the web methods
(functions) that a service will accept
-

the inputs that
go into these methods, and the format of the output
that can be expected in return.

Answer
-

False


True or False?


UDDI is a standard for establishing and using
public registries of web services.

Answer


True


Web Services usually exchange XLM
instructions via email or HTML.

Answer
-

True


What is SOAP?


SOAP


S
imple
O
bject
A
ccess
P
rotocol


SOAP is a platform independent set of syntax
rules used to call methods located on diverse
distributed systems.


XML Documents are transported via HTTP
through firewalls without risk.


A SOAP message is just an XML message
that follows a few additional rules.


What SOAP Does…


Messages are sent in a Request / Response
fashion.


Defines an XML structure to call a method,
pass the method parameters and return the
requested values.


Returns error values (faults) if the service
provider cannot execute the requested
method.


What SOAP does not do…


The SOAP specification does not define how
the requester or the responder send or
receive messages.


Does not define how a message will create
an instance of an object and execute the
method.


Implementation details are left to the software
developer.


Why SOAP is good!


Soap will allow developers to use/reuse code
from know and trusted sources.


Makes it possible for systems to become
highly distributed.


Flash Video about SOAP:

Play Video


What is XML?


XML
-

Extensible Markup Language


A set of rules, published by the W3C (World
Wide Web Consortium), for building new
languages.


XML


Well Formedness


The specific rules with which all XML
documents must comply in order to be
minimally legitimate XML


Examples


element and attribute names are case
-
sensitive.


attribute values must be enclosed in single or
double quotation marks.


Every start tag must be balanced with one end
tag.


XML


Important Characters


The only characters you
must

be able to represent
are:


the less
-
than and greater
-
than "angle brackets," < and >


the forward slash, /


the single quotation mark or apostrophe, ‘


the double quotation mark, “


the ampersand, &


and the semi
-
colon, ;



Some optional features of XML will be accessible
only if you also have such punctuation marks as an
exclamation point, !; a dollar sign, $; and an @ sign.

XML Continued


The most important characters in a XML
document are the <, >, and /


No XML document does not include these.


Each well
-
formed XML document has one
and only one "outermost element," within
which all the others are nested. This
outermost element is called the
root element.


More XML…



As with HTML, XML documents depend on
you being able to interpret them.And for that
you need a data type document (DTD)


Browsers have an XML DTD built in so you
could just let them know you are using XML


<?XML version="1.0" standalone="yes"?>


Or alternately, you can also write your own
and send it along with your code.


Even More XML…


The two main types of XML pages are the
"standalone" and those that use a DTD.


With standalone the page stands alone
relying on the browser to have the XML DTD.


The other type of page offers the DTD to the
browser so it can run the page.


Multiple Choice


An XML document that adheres to common
syntax is called:


a. well written


b. extensible


c. well formed


d. compliant

Answer
-

C



Which of these characters is optional in XML
coding?


a. greater than >


b. less than >


c. percent %


d. slash /

Answer
-

C


True or False?


A DTD is a document about how to interpret
HTML or XML


Answer
-
True



In an XML document IMG and img refer to
the same thing


Answer
-
False