RE: Issue 4951 -- Reformulation

+1

Christopher Ferris
STSM, Software Group Standards Strategy
email: chrisfer@us.ibm.com
blog: http://www.ibm.com/developerworks/blogs/page/chrisferris
phone: +1 508 234 2986

public-ws-policy-request@w3.org wrote on 09/25/2007 12:34:59 PM:

> 
> Ashok,
> 
> I had long thought that XML and Web services needed a generalized
> solution for embedding the "order" of operations in the instance
> document. 
> 
> I proposed a simple model at the XML processing model workshop many
> years ago.  But it seems to me that things "kind of work" without it.
> Imagine a document that is described/defined by XML Schema with an
> Xinclude and XSLT.  Schema gets done first, then "typically" Xinclude
> then XSLT.   Now obviously the order of these could be inverted for some
> useful applications.  But the complexity of the solutions, such as the
> one embodied in Xproc, seems to outweight the benefits of a "default"
> processing order.  Now it may be that Xinclude deployment has been slow
> because there hasn't been an order of processing.  But I'm always leery
> of blaming lack of adoption of one technology on missing other
> technology because that "problem" usually means that the first
> technology is problematic or there is low demand.  If there was demand,
> it would happen.
> 
> The topic also came up at the Web Services Workshop, in the Web Services
> Architecture Working Group, and in each of the WS-* working groups or
> TCs.  I remember being dismayed that WS-Security was the "first" out of
> the chute for WS-* specs and only specified order for security.  What if
> RM needed to happen in between signing and encrypting?  But, it seems
> that if we again adopt a default model of security last on outbound and
> first on inbound, we can hit the 80/20 point of applications vs
> complexity.  The number of applications where order matters that cannot
> be solved by the current technology seems small. 
> 
> I will observe that this "default" order appears to bring back the
> notion of layering of protocols that the flat SOAP header structure
> dispensed with.  In the example of RM + Security, we do this "on the
> web" by using tcp/ip then layering SSL.  This "layering" is approximated
> in SOAP by having security always last, aka another layer. 
> 
> Having said all that, if we imagine what a solution might look like that
> would allow order of assertions, then there appear to be considerable
> complexities that emerge.  For example, if we wanted the ws-security
> applied to all headers, then RM applied after, then the new "order"
> header inserted, we'd have this multi-pass security model.  The RM
> header and the new order header would probably need some kind of
> security, otherwise what's the point of having the rest of the message
> secure?  The choices are: 1) have a message with security on most but
> none on RM and Order of processing; 2) re-apply security after the RM
> and Order of Processing meaning there are 2 passes of security. 
> 
> I find it hard to justify the costs to develop such technology for the
> limited applications.  I think what's really needed is at least one
> "killer app" where Order of processing had to be in the message, and I
> haven't heard anything other than "abstract" or "what ifs". 
> 
> Cheers,
> Dave
> 
> > -----Original Message-----
> > From: public-ws-policy-request@w3.org 
> > [mailto:public-ws-policy-request@w3.org] On Behalf Of ashok malhotra
> > Sent: Wednesday, September 12, 2007 11:55 AM
> > To: public-ws-policy@w3.org
> > Subject: Issue 4951 -- Reformulation
> > 
> > 
> > Here is a reformulation of issue 4951 based on discussion on 
> > morning's telcon.  Thanks to Paul Cotton for contributing to this.
> > 
> > The issue has to do with ordering between assertions.  The 
> > spec says that users can write special assertions that 
> > control the ordering between assertions.  Examples are the 
> > "sign before encrypt" and "encrypt before signing" assertions 
> > in WS-Security Policy.  But the interesting issues come up 
> > when ordering is desired between assertions from different 
> > domains, for example adding RM headers and encrypting the 
> > headers.  In such cases, which namespace does the ordering 
> > assertion go?
> > 
> > The other response to this issue is that the semantics of 
> > each assertion includes the ordering information.  I think 
> > this is  problematic.
> > 
> > Consider a universe of assertions U  that includes assertions 
> > A1, A2, ... An.  Assume  further that  the semantics of each 
> > assertion Am indicates its ordering wrt all other assertions 
> > in U ... or at least the assertions where ordering matters. 
> > Now, we add another assertion X into the universe U.  Not 
> > only do we need to specify the order of X wrt all the 
> > assertions in U, we have to change the semantics of all the 
> > existing assertions in U to specify the order wrt X.  This 
> > seems to be a problem to me.
> > --
> > All the best, Ashok
> > 
> > 
>