[Crm-sig] issue 336 and spacetime volumes

Martin Doerr martin at ics.forth.gr
Sat Mar 23 20:25:55 EET 2019


Dear Francesco,

Here a more complete comment. I widely agree anyway.

On 3/21/2019 12:49 AM, Francesco Beretta wrote:
>
> Dear Martin, all,
>
> Applying the principles we generally use in conceptual modelling, a 
> model of « CRM top hierarchy and space&time » like the one you’ll find 
> in attachment seems plausible. I’ll comment the slides from the top to 
> the bottom, for the sake of clarity.
>
>
> Let’s start from the basic modelling principles Martin expressed on 
> 9/3/2019 :
>
> « In the first place, E2 has a substance of "phenomena" something 
> "becoming" "changing" "moving", "interacting". In addition, we 
> interpret it now also more statically as including a sort of 
> maintaining something. It is _necessarily connected_ to some "things" 
> on which such interactions, changes or temporary, non-essential 
> formation of properties happen, but we have seen so far no good 
> general way to describe the ways of involvement at the level of E2.
>
> E92 is nothing of that kind. It is just spacetime, the generalized 
> space in which we live and think, not what is there not what happens 
> there. It is just a "where". It is further a volume in that space, 
> i.e., it must have some inner part, and a surface as fuzzy as it may 
> be, and a way to identify it. »
>
>
> As you can see in the attached slides (the more relevant being the 
> first one), E77 Persistent Item and E2 Temporal entity are 
> ‘phenomenal’ classes. In contrast, Place, Time-Span, STV, Dimension 
> are ‘regions’ in a reference ‘space’, be this spatial, temporal or 
> quantitative.
>
There is a curious difference of the STV to Place, TimeSpan and 
Dimensions. Points in spacetime are absolute in the world in which we 
live, at least in modern physics, and in our intuition. They are the 
"where this happened". If we describe them by coordinates, we use 
different reference 'spaces' in the physical space, and in time. But 
their identity does not depend on them. Therefore, descriptions in one 
reference 'space' can be transformed into descriptions of the same 
points in another, if the relations are known. This makes a fundamental 
difference.
>
>
> As we know, E77 Persistent Item instances are in principle not 
> directly related to time (using properties) but they live in time : we 
> model this using temporal entities related to these Persistent item 
> instances « on which such interactions, changes or temporary, 
> non-essential formation of properties happen » (Martin). Temporal 
> entities are phenomena we usually perceive or observe in relation to 
> some persistent item, be this a conceptual or physical one. A very 
> general property ‘Pxx involves/concern’ would clearly express this 
> basic phenomenon : persistent items live in time (and space) and we 
> model this using temporal entities (Events for dynamic moments, Phases 
> for static characteristics, both phenomenal).
>
Indeed, but it violates the bottom-up methodology to define a property 
which is not well-distinguished from others, and possibly the Open World 
assumption, trying to cover all future relations between two classes. It 
satisfies the theoretical understanding, but is error-prone for data 
modeling. We should only accept if good definitions are found.
>
> E2 Temporal entities (having a phenomenal substance) are projected in 
> a region in time and these contribute to define their identity (we 
> stress here the phenomenal aspect, not the epistemological). This 
> projection in time is modelled as an instance of E52 Time span.
>
Yes. Without theory or relativity, this projection is unique except for 
the zero point. With theory of relativity, it depends on the reference 
'space'. With GPS satellites, the correction makes up for an error of 
about one km on the surface of Earth, if I remember correctly.
>
> Insofar as we are modelling conceptually we need to keep these two 
> classes (E2, E52) separate in the model regardless their cardinality 
> because they are expressions of significantly different substance. The 
> implementation in an information system, if the (1,1;1,1) cardinality 
> is chosen, can merge the two classes but this is about implementation 
> not about the conceptual model : here we must keep both classes 
> separate for the sake of clarity and consistency with the identity 
> principles.
>
I agree.
>
> How do we model, in the next step, projection in physical space ? The 
> crucial question is: are there any temporal entities without such a 
> projection ? If yes (e.g. I2 Belief), we have two ways of modelling 
> this : 1) with a (*1*,1:1,1/n) cardinality for /P7 took place at 
> /associating it to E4 Period (slide 1) or 2)
>
Besides that P7 allows for defining wider areas, spacial projections are 
not unique. They depend on reference frames, which are in general 
moving, be it geologically slow or faster. Therefore (1,1: is wrong).
>
> with a (*0*,1:1,1/n) cardinality associating it directly to E2 
> Temporal entity (slide 2). This second model would imply in some cases 
> there is not a projection of a Temporal entity instance in a region in 
> physical space, although fundamentally there can be one. In the 
> perspective of simplicity, the second solution would be the preferable 
> one.
>
I can only repeat, that if we accept this argument, for questions of 
simplicity all properties should be at CRM Entity. It is really a trap, 
because the ways an E2 may occur in physical space needs not qualify as 
an "extent in space".
>
> But for the sake of consistency with earlier versions of the CRM and 
> for making the conceptual model more clear and explicit, the first 
> modelling choice (using E4 Period) would probably be the best one.
>
This is not a question of the CRM, but a fundamental modelling principle 
of ontology. We are committed to understand the "οντα". So far, it has 
saved us from many modelling errors and pseudo-solutions, causing 
incompatibilities with other "simplified" high-level theories.
>
> Insofar as it has a projection in time and space, an instance of E4 
> Period (which is composed by Events and Phases) is associated to a 
> Spacetime Volume. As phenomenon, an instance of E4 Period makes a STV 
> to be virtually present : if we want to make this explicit, and 
> especially if we want to explicitly associate a time span with a 
> place, providing this association with a specific identity, 
> independently from any E4 Period instance, we need a STV instance (and 
> the E92 STV class). For this we would then need to have a property 
> /Pxx has //spacetime//volume/ (1,1:1,1/n) modelled similarly to P4/P7.
>
In contrast to Place and Time-Span, this volume is unique. It is 
(1,1:1,1). It has exactly the same projections to Place and Time as the 
E4, and therefore is definitely not similar to P4/P7. Please refer to 
texts about CRMgeo.
>
> Incidentally, for all these properties we have to decide if the 
> maximum cardinality on the side of a Exx Region subclass has to be 1 
> or n. If we choose ‘n’ we provide a specific identity to the Exx 
> Region instance, independently from the identity of the related 
> Phenomenal Class instance. E.g. different E4 Period instances could be 
> located in the same spatial region, i.e. E53 Place.
>
Yes, this is correct for P7, but not for the projection. The projection 
is unique per reference system. No other phenomenon will have exactly 
the same extent. See CRMgeo for more detailed argumentation.
>
> If we think an autonomous identity of E92 STV is not given, and time 
> and space, and virtual spacetime volume (= time + space) are always 
> related to at least one temporal entity or period (i.e. to a phenomenon),
>
This is not the case, because we have the declarative STVs in cRMgeo.
>
> then we could deprecate the E92 Spacetime Volume class and use E4 
> Period instead as common point of meeting of time and space, in the 
> phenomenal sense. A E53 Place being the ‘surface’ of a phenomenon 
> during a given timespan. E93 Presence (as subclass of S4 Observation?) 
> would be an intersection of time and space in the epistemological 
> sense, providing an arbitrarily defined snapshot of a Period. As such, 
> it would have a specific identity and would be modelled as a distinct 
> class.
>
Correct. We could move the whole stuff to CRMgeo, and allow it to have a 
huge superclass out of CRMbase. That was what we wanted to avoid, but we 
could change that.
>
>
> This way of modelling seems to be more robust and consistent with the 
> domain : we model phenomena in cultural life associated to persistent 
> items, phenomena having a projection in time and space, not 
> time/space/STV as such, independently from phenomena.
>
If we make multiple ISA, it *means *that both concepts, E2 *AND* E92 are 
specialized! The specialization of E92 in E4 is to be in addition 
phenomenal. See CRMgeo.
>
> Also, this would avoid the issue of the redundancy of properties which 
> was the starting point of this discussion : P4/P160 ; P7/P161. For 
> these reasons I would advocate to abandon the E92 class, knowing that 
> it is virtually present in E4 Period as its implicit spatio-temporal 
> surface.
>
See above. The redundancy of property here is more crying out for a 
common superclass on top of E2 and E92.
>
> The last issue I see is the one related to modelling of a STV for a 
> E18 Physical thing. The /difference/ between the volume occupied by a 
> physical body as such, be it moving or not, and the volume occupied by 
> the body moving from one place to another, is not clearly defined if 
> you make a E18 Physical thing a subclass of E92 Spacetime volume.In 
> the well known case of the vessels’ fight in Trafalgar, the TSV of the 
> fight can be treated as projection in time and space of the whole 
> event, using P4/P7 and, if needed, the correspondent declarative 
> properties : we have a phenomenon, the fight (E5 as temporal entity), 
> and a document driven approximation of its STV using in SP10/SP2 
> (without necessarily the need of using a E92 Spacetime volume/SP7 STV 
> classes as separated entities with an own identity).
>
Basically, this is a misunderstanding of the nature of an STV. The STV 
is not the result of a backprojection of a space and a time.

Just the opposite. The moving around of the spatial volume of a physical 
body IS the STV. It is all spatial points where the volume was one 
instant of time after another. he TSTV of the fight cannot be treated as 
projection in time and space of the whole event. It is the STV of the 
event that has such projections. The resulting box of the two 
projections is containing/approximating the event's STV. We need to 
understand that!

> On the one side, Nelson’s ship itself, as an instance of E18 Physical 
> thing, would have a time related volume (STV), even being moored in a 
> port without moving, and the wreck of it on the seafloor has a STV 
> different from the navigating ship. But this is not about the position 
> in the fight but about the volume of the Persistent item instance 
> itself (this volume being a E53 Place instance, as specific « extent 
> in space » : the 3D ‘surface’ of the ship) and can be modelled using a 
> Exx Volume/Surface class, modelled as subclass of E3 Condition state.
>
Well, this is just inventing a new term for the phenomenal STV, if I am 
not completely mistaken?
>
> E3 would be modelled directly as subclass of E4 Period or as subclass 
> of the new Exx Phase class, expressing « phases during the existence 
> and evolution of an instance of E18 Physical Thing characterized by a 
> substantial appearance » (Martin). In this case the ‘appearance’ is 
> the volume of the physical thing understood as a « surface » with a 
> precise form. The movement of the ship, on the other side, can be 
> modelled as an instance of E5 Event and associated to the fight E5 
> Event instance using P9 consists of.
>
See above. Note, that the spatial projection of the STV of the ship on 
the ship as reference space stays within the ship all time, but the 
projection of the STV on the seafloor is a long path. The spatial 
projection of Nelson's body on the seafloor is within this path., and 
within the ship in the other projection.
>
>
> This approach would allow to have a concise and straightforward model 
> and avoid inconsistency with the CRM well established way of defining 
> identity criteria, which isn’t the case if E4 Period and E18 Physical 
> thing are modelled as subclasses of E92 Spacetime Volume (insofar as 
> this is not a phenomenon but a ‘region’ in space and time).
>
Just let me repeat, the inconsistency we are discussing is that the 
projection of the event points in an E4 on time occurs as P4 and as 
P160, regardless whether we make E4 an STV or not, or if we rename E92 
to something else.

All the best,

Martin

>
> All the best
>
> Francesco
>
>
>
>

-- 
------------------------------------
  Dr. Martin Doerr
               
  Honorary Head of the
  Center for Cultural Informatics
  
  Information Systems Laboratory
  Institute of Computer Science
  Foundation for Research and Technology - Hellas (FORTH)
                   
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