- From: Paolo Missier <Paolo.Missier@ncl.ac.uk>
- Date: Sat, 25 Jun 2011 19:31:02 +0100
- To: public-prov-wg@w3.org
I have added some comments to the "smaller example" page: http://www.w3.org/2011/prov/wiki/FileExample#Comments_.28Paolo.29 in an attempt to understand the definitions. There is also a pretty picture that tries to capture the gist of the example. See if you like it I believe I fundamentally agree with Jim when I rename "invariant properties" to "properties whose value is constant across a time span or a sequence of observable events (which may include transformational processes)". Time is tricky though, as we know, because of the issues with distributed clocks potentially being used by different observers. -Paolo On 6/24/11 8:44 PM, Myers, Jim wrote: > I think it's possible to consider the invariance to be defined in terms of processes (in the same sense we discussed time not necessarily being core but useful corroborating evidence on the weekly call): B is a view of A implies that some of the processes that are part of A's lifecycle are things that start/end the existence of Bs. That maps to time in that there are time intervals when no such processes occur during which a view exists and the properties that define that view don't change (for A or B). > > I know I'm sliding close to the 'invariant properties integral to identity' discussion by saying 'properties that define the view' but my sense of that discussion was that really about a strict sense of integral to identity versus a distinguishing feature of, and both are OK - there's a set of properties that are either integral to B's identity or distinguishing features of B that together define what type of thing B is. And the processes that modify those properties are the ones we're documenting with the provenance statements. > > Jim > > >> -----Original Message----- >> From: public-prov-wg-request@w3.org [mailto:public-prov-wg- >> request@w3.org] On Behalf Of Stian Soiland-Reyes >> Sent: Friday, June 24, 2011 12:03 PM >> To: public-prov-wg@w3.org >> Subject: Re: Definitions and provenance and invariance >> >> On Fri, Jun 24, 2011 at 14:33, Paolo Missier<Paolo.Missier@ncl.ac.uk> wrote: >> >> >>> I initially thought "invariant" was relative to Time, but it is not >>> the case. so what is invariance relative to, here? all possible views >>> of this particular rectangle A? but then we are back to "properties >>> that are integral to identity", which I thought we had dropped >> Invariant *is* relative to time, or immune to changes if you like. >> >> See http://www.w3.org/2011/prov/wiki/FileExample : >> >> i0: A file, for which we have a property name (/home/towns.txt) and a >> property creator (Alice), which are invariant in the interval [t,t+4[ >> i1: A file (i0) with added property content which is empty; it exists in the >> interval [t,t+1[ >> i2: A file (i0) with added property content with value London and Edinburgh; >> it exists in the interval [t+1,t+3[ >> i3: A file (i0) with added property content with value London, Edinburgh, NY, >> LA; it exists in the interval [t+3,t+4[ >> >> So invariant properties are properties which can not change over the lifetime >> that for *that* IVPT. In the example here the content of i0 is changing over >> its lifetime, but its name and creator are immutable. >> The name might or might not be integral to identity, but we are not saying >> anything about that. In i2 the content is immutable as well (but perhaps not >> the "last accessed time" property). >> >> When we want to say that Charles is emailing the file content, we want to say >> "the file with this particular content". So we'll say that the email i4 is derived >> from i2 - which is a view of i0 for the period when the content was >> London/Edinburgh. It might not be important exactly when that was, or what >> was before or after, as long as we are able to distinguish i2 from i1 and i3. (In >> fact, in a distributed setting, Charles might well attach the i2 content after >> David has added NY and LA - perhaps his Dropbox had not synchronized yet) >> >> >> > From this, if B is an invariant of A - then properties they share must >> have corresponding values - so over that time period all the immutable >> properties of B should correspond to (possibly mutable) properties in A. >> >> I guess it depends on the 'corresponding' if this means that those properties >> are unchanged in A during B's life span - and (just thought about this) - if B >> stays being an invariant of A over B's life span. >> >> >> (BTW - why are we saying View Or Perspective - when is it Perspective and >> when is it a View?) >> >> -- >> Stian Soiland-Reyes, myGrid team >> School of Computer Science >> The University of Manchester -- ----------- ~oo~ -------------- Paolo Missier - Paolo.Missier@newcastle.ac.uk, pmissier@acm.org School of Computing Science, Newcastle University, UK http://www.cs.ncl.ac.uk/people/Paolo.Missier
Received on Saturday, 25 June 2011 18:31:34 UTC