[OGSA-D-WG] Fw: Definition of data consistency

Wed Oct 10 03:47:09 CDT 2007

I like this approach.

Is it worth embellishing it as follows:

Data consistency: An instance of data in one resource in a distributed
system is said to be "consistent" with one or more other instances of
that data elsewhere in the system if it is up-to-date with respect to
those instances. 

In a given system a policy may define the rules for determining the
extent to which data is up-to-date, and for maintaining that degree of
consistency.

The changes are:

paragraph 1 - to talk about different resources in a distributed system
(putting some context on "data instances", which is not a term we
define).

paragraph 2 - to introduce the notion of a degree of consistency rather
than simply consistent/inconsistent.

I don't feel strongly about either of these - what do others think?

Dave.
  _____  

	From: ogsa-d-wg-bounces at ogf.org
[mailto:ogsa-d-wg-bounces at ogf.org] On Behalf Of Allen Luniewski
	Sent: 09 October 2007 17:50
	To: ogsa-d-wg at ggf.org
	Subject: [OGSA-D-WG] Fw: Definition of data consistency

	Please see Jem's note below - he can not post to this DL.

	I think that his suggestion is a good one.

	Allen Luniewski
	IBM Cross Brand Services
	IBM Silicon Valley Laboratory
	555 Bailey Ave.
	San Jose, CA 95141

	408-463-2255
	408-930-1844 (mobile)

	----- Forwarded by Allen Luniewski/Almaden/IBM on 10/09/2007
09:49 AM -----

				"Treadwell, Jem" <jem.treadwell at hp.com> 

				10/09/2007 09:40 AM

To

Dave Berry <daveb at nesc.ac.uk>, Allen Luniewski <luniew at almaden.ibm.com>	

cc

Subject

FW: [OGSA-D-WG] ***SPAM*** Definition of data consistency	

	Allen/Dave, I can't mail the data mailing list, so please feel
free to pass this on if you think it's worthwhile.

	I agree with Allen about sounding specific, and this is a hard
thing to turn into a direct definition without using some term such as
"indication." You might think about using an indirect form:

			Data consistency: An instance of data is said to
be "consistent" with one or more other instances of that data if it is
up-to-date with respect to those instances. 

	That may be enough, but you could also add something like: 

			In a given system a policy may define the rules
for determining whether data is up-to-date, and for maintaining
consistency.

	- Jem

	Jem Treadwell 
	Software Engineer 

	HP ESS Software
	856.638.6021 office | 856.638.6190 fax | jem.treadwell at hp.com
<mailto:jem.treadwell at hp.com> 
	6000 Irwin Road | Mount Laurel | NJ 08054
	http://www.hp.com/go/vse <http://www.hp.com/go/vse>  

	  <http://www.hp.com/go/software>  
  _____  

	From: Allen Luniewski [mailto:luniew at us.ibm.com] 
	Sent: Monday, October 08, 2007 5:20 PM
	To: Dave Berry
	Cc: Treadwell, Jem; ogsa-d-wg at ogf.org
	Subject: Re: [OGSA-D-WG] ***SPAM*** Definition of data
consistency

	Dave,

	I think that I am okay with that suggested change. I am a little
bit worried about using the word "measure" as it can be taken to imply
things that we really do not want to address (e.g., a means to measure
and a quantifiable scale for measurement). I thought about suggesting
changing "A measure" to "An indication" but that seems just a bit too
vague to me. I don't have a better suggestion right now.

	Allen Luniewski
	IBM Cross Brand Services
	IBM Silicon Valley Laboratory
	555 Bailey Ave.
	San Jose, CA 95141

	408-463-2255
	408-930-1844 (mobile)

	 "Dave Berry" <daveb at nesc.ac.uk> 

					"Dave Berry" <daveb at nesc.ac.uk> 
				Sent by: ogsa-d-wg-bounces at ogf.org 

					10/08/2007 02:11 PM

To

<ogsa-d-wg at ogf.org>	

cc

"Treadwell, Jem" <jem.treadwell at hp.com>	

Subject

[OGSA-D-WG] ***SPAM*** Definition of data consistency	

	Jem queried our definition of data consistency, which is
currently: 

A policy that specifies or describes how up-to-date an instance of data
is in one service of a distributed system, with respect to one or more
instances of that data elsewhere in the system.	

	Jem said (in e-mail): 

	my thought was that data consistency would be a state of the
data - it's consistent w.r.t. some other set of data or it isn't; the
policy would be the rules that determine whether it is, and what the
requirements are. 

	I've had a look through our document and I agree. We refer to
data consistency policies but also to data consistency requirements,
mechanisms and strategies.

	So, how about this as a revised definntion:

	"A measure of how up-to-date an instance of data is in one
service of a distributed system, with respect to one or more instances
of that data elsewhere in the system." 

	Best wishes,

	Dave Berry 
	Deputy Director, Research & E-infrastructure Development 
	National e-Science Centre 
	15 South College Street, Edinburgh, EH8 9AA 
	+44 131 651 4039 www.nesc.ac.uk <http://www.nesc.ac.uk/> 
	--
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