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From "Alistair Hopkins" <alist...@berthengron.co.uk>
Subject RE: XML based system architecture
Date Thu, 03 May 2001 08:16:55 GMT
Why do the tiers need to be on different machines?

My app works on a very clear MVC architecture:

Request ----> Controller ----> BL ----> Controller ----> XSLT
processor ----> Response
	HTTP			INTERNAL		RETURNS		PROCESSES 		WHATEVER
				WRAPPER		XML			XML TO ...		[Currently HTML, XML, CSV, pdf]
				ROUND
				REQUEST

The request URL is therefore constructed to say what action/information is
required AND how it is to be presented
eg \controller\Order?order_no=1034&csv=true for a spreadsheet of order 1034.

If I need to return raw XML over http I just tell it to forget the XSLT view
processing stage.

If I need to scale, I will load balance, as all of this happens within a
webapp (the controller is just a servlet which loads the relevant Action
(BL) which the URL specifies)

It's all a lot easier than other RPC, etcetera

Alistair


-----Original Message-----
From: mx2@dais.cro.st.com [mailto:mx2@dais.cro.st.com]On Behalf Of
Xavier MACHENAUD
Sent: Wednesday, May 02, 2001 4:28 PM
To: general@xml.apache.org
Subject: Re: XML based system architecture


This is fine with a 2 tier architecture because XML servers can do SQL
queries.

But it becomes more complicated if you want to do more generic requests
(not just SQL) to a business logic (BL) layer.

In my case, I also like to be able to pass on the authentication
information and to add a load-balancing mechanism later on in front of
the BL.
That's why I was thinking of a BL server accessible via HTTP.

That's why I was thinking of a way to do an HTTP request from the XML
server, do get to a sort of servlet chaining.
Am I going to a wrong way thinking that?
If not, how can I do servlet chaining from the XML server?
Should I implement a tag library that will allow me to do servlet
chaining? (or to make and XML-RPC/SOAP call if my BL server is an
XML-RPC/SOAP service)

Xavier

lyndon.samson@ssmb.com wrote:
>
> You could use XML-RPC ( simpler ) or SOAP ( more functionality ).
>
> I did something similar, but only 2-tier distributed.
>
> Outbound
>  XML -> SQL - > XML -> HTML
>
> Inbound
>  HTML FORM -> XML -> SQL
>
> ie for Outbound
>
> <queryset name="listCustomers">
>   <sql>select * from customers</sql>
> </queryset>
>
> select * from customers;
>
> <customers id="1">
>  <name>aaa</name>
>  <address>123 abc</address>
> </customers>
> <customers id="2">
>  <name>bbb</name>
>  <address>456 xzy</address>
> </customers>
> ...
>
> ...
> <table>
>  <tr><td>Name</td></td>Address</td></tr>
>  <tr><td>aaa</td></td>123 abc</td></tr>
>  <tr><td>bbb</td></td>456 xyz</td></tr>
> </table>
> ...
>
> -----Original Message-----
> From: Xavier MACHENAUD [mailto:xavier.machenaud@st.com]
> Sent: Wednesday, May 02, 2001 10:23 AM
> To: General@xml.apache.org
> Subject: XML based system architecture
>
> Hi,
>
> I'm in the process of designing an XML based application and I'm running
> into a problem.
>
> I want to separate the Presentation layer (XML server) and the Business
> Logic layer (servlet/cgi/...) by using XML : the presentation layer is
> querying  the business logic layer which is returning XML data.
> Of course, I don't want my BL layer to do any output formatting.
>
>         http
> +-----+ get/post  +-----+       query         +-----+
> |user | --------> |     | ------------------> |     |
> |agent|           |Pres.|                     | BL  |
> |     | <-------  |layer| <------------------ |layer|
> +-----+  html     +-----+        XML          +-----+
>          pdf      Xml Server                Servlet/cgi/...
>          wml
>
> My problem is how can implement such an architecture?
> More specifically, what protocol (compatible with that fact that there
> could be a firewall between the 2 layers) can be used to query the BL
> servlet?
>
>
> Cheers,
> Xavier
>

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