Sunday, February 17, 2008

The weight of the baby

HL7 RIM, as we have pointed out on too many occasions, confuses observations with the entities observed. To illustrate this confusion once again, we provide the following scenario, from Werner Ceusters (WC), with reactions from Dan Russler (DR), as they appeared on the HL7 vocabulary list. (Dan played a key role in the development of the HL7 Reference Information Model.)  We added some small clarifications and corrected some spelling errors (and perhaps, by trying to work our way through the numerous levels of comments on comments, we might have overlooked some dependencies). Dan and Werner are free to suggest corrections. (To access the Archives of HL7 lists one can go to:

Here we go:

WC to DR: I am in a delivery room, and there is that baby and his weight. When I want to register something about that baby's weight, I will use the symbol "#w-1234" to denote that baby's weight. The numbers are there to differentiate that baby's weight from some other baby's weight. The baby's weight is something that has different values at different times. The baby's weight endures through time. It is a continuant.

I want to obtain a value for the baby's weight, for which I have to perform an act of measurement, for which I will use the symbol "#m-5678". The ID numbers are there to differentiate that measurement from other measurements I might perform, even from the measurement which I might do a few minutes later when I weigh the same baby for a second time. The act of measuring occurs at a time. It is an occurrent.

The act of measuring gives me a magnitude, which in this case is something we have been taught to register as "4.7 kg". Now registering that (entering "4.7" into a computer, for instance) is an act in its own right, and when I want to refer to that registering act, I will use the symbol #r-881 (you get the picture, I hope).

Now you (Dan) seem to argue that I am not allowed to assign some of these symbols, though I can't figure out from your comments which one(s) precisely you object to. You should clarify. Here are the symbols again, for easy reference:

#w-1234 : THAT baby's weight
#m-5678 : THAT process (which occurred during THAT time) of measuring THAT baby's weight
4.7 kg : the value obtained for THAT baby's weight through THAT process
#r-881 : the further process of entering the obtained value in some record
DR: The baby is a collection of molecules ...

WC: Sure; but that is not relevant here.

DR: Why isn't the fact that the baby is made of molecules relevant? ... The baby wouldn't have a weight without being made of molecules.

WC: If the task is to register the magnitude of that baby's weight in a record, there is no reason to mention his molecules. We also don't talk about those other molecules on the side of the Earth that attract the baby's molecules, do we ?

DR: The weight is the measurement of the force of attraction between the baby's molecules and the earth at that location and at that point in time.

WC: "No" on several things. First, the weight of the baby is not a measurement at all.

DR: You will need to go back to the physics definition of weight. Objects have mass, which create a mutual force of attraction.

WC: Thanks for this lesson, again; although I said in my mail that I knew that. It is simply not relevant.

DR: Weight is simply the concept of putting a scale in between two masses and measuring the force of attraction between two masses, the baby and the earth. You could abstract out the idea of measurement, but then we would just say "force of attraction," not weight. Of course the force of attraction between the baby and the earth is less in Denver than at sea level. So perhaps you could alter your discussion to match the real physics of the situation?

WC: That doesn't change anything to the simple task at hand: putting a baby on the scale, and reading what the instrument gives as weight. Dan, stick to the topic.

DR: Now this illustrates the problem with comparing "your reality" to "my reality."

WC: There is only one reality, but we can describe it in different ways. Your way seems to be to lump important things together (e.g. that baby's weight and my activity of measuring that weight), and to add irrelevant things (such as the molecules of the Earth)

DR: You invent things in your mind in the discussion below that I have not invented in my mind.

WC: I didn't invent anything. I gave a description of a simple scenario and I introduced 4 symbols. You started to mix and confuse the symbols, and bring in others.

DR: When you communicate what you invent, you use words that mean something different to me (and to many other people). Although I respect the inventions of your mind, I don't understand them, and when you explain them, I don't always agree with them.

WC: Then, if you still don't understand the scenario I described, and what the four symbols stand for, give me a language in which I can describe it so that you will understand it.

There is something that you can measure (the baby's weight), and an act of measurement, which is a different thing. The value for the weight that you obtain by measuring it is yet another thing. The word "measurement" is often used ambiguously to denote the last two things: the measuring act and the value obtained through the measuring act. It would be good for everybody's understanding not to use language ambiguously in this way. (Compare it with the noun phrase "the cut" which is used for both the act of cutting and the gap that results from this act.)

[Ceusters here tries to describe what at first might seem hard to swallow: the weight of this baby is the same entity from one time to the next. It is an enduring attribute of the baby. Certainly the baby's weight changes over time, but then so also does the baby. But just as the baby stays the same individual from one time to the next as it changes, so also does its weight. The baby's weight is a continuant. At any point in time, that weight has a precise magnitude, but which magnitude this is changes from one time to the next. - BS]

The discussion continues:

WC: All that gravity stuff is irrelevant here, because if I or a nurse put a baby on a scale to measure it's weight, I know what I'm measuring. I was and I am not talking about other stuff you can measure.
Again, I will use the symbol "#w-1234" to denote that baby's weight.

DR: Werner has in his mind the idea of "the force of attraction" and created a symbol #w-1234 to communicate the force of attraction between the baby's molecules and the earth at that point in time.

WC: No on several things, again: I had nothing regarding forces of attraction in my mind. In fact, I was describing a concrete delivery room situation.

DR: Doesn't gravity exist in the delivery room? Gravity sounds pretty concrete to me.

WC: Sure, but this fact is irrelevant. There are at least a billion other things in that room, such as the molecules in the door knob. I used explicitly demonstrative particles to make it clear: There is "THAT" baby. I'm not talking about conceptual representations of babies and delivery rooms, but simple things: babies and rooms.

"#w-1234" is the symbol that I use to denote that baby's weight in a description, NOT the magnitude of the weight.

DR: Now this symbol "#w-1234" has attributes associated with the symbol, such as:
time (since the weight will vary with time);
location (since the weight will vary with the location, e.g. altitude);
identity of the baby (weight will vary with different babies).
WC: Many more "no's". The symbol "#w-1234" may have attributes associated with it, but I did not talk about that.

DR: on the contrary, you gave the symbol attributes "the symbol #w-1234 ... to denote that baby's weight". To transform to a formal propositional grammar:
the symbol #w-1234 dentotes the weight of that baby
object of the predicate: "that baby"
predicate: "denotes the weight"
WC: Dan, the symbol I introduced here is "#w-1234". I told you what the symbol stands for: that baby's weight. You can decompose that in as many ways as you want and I can give fifteen other grammars and NLU paradigms for you to analyse the way I said things; but you must at some stage get back to the topic. We are not analysing the lines of text that I produced, we are analysing what the lines of text try to convey. But the fact that you insist on analysing it this way, demonstrates that you are not able to get passed the language level.

Let's try it this way: "#w-1234" is a symbol. It is composed of the characters "#", "w", etc. I use it in a language to refer to / to stand for that particular baby's weight, a particular entity in reality, not an element of a language. I could use another symbol for that baby's weight. Thus I could use the symbol "that baby's weight'. I could then say "that baby's weight" stands for that baby's weight.

Attributes of the symbol may be the number of characters, the font used, etc. I am not studying symbols for the sake of this discussion. But interestingly, Dan, it is becoming clear at this point that you (perhaps because of the inadequacy of the representation language you choose to use) confuse the symbol with what the symbol stands for, a common mistake made by people who misunderstand semiotics, and a confusion which pervades the entire RIM, as we and others have shown.

Dan, it is surely the case that the words I used in the language of that paragraph are symbols, but we are not talking about the language in that paragraph. We are talking about the state of affairs in reality of which that paragraph is a linguistic representation. And you darned well know it, Dan, come on.

DR: I just tried to understand what you mean (perhaps not always in the same way as what is in your mind) or what the relationship is in your mind to what is occurring in the delivery room.

WC: I told you: that is irrelevant. That is "Wusteria". If I am talking to you about my mother, then I am not talking to you about some neuronal blurb in my brain. I am talking about my flesh and blood mother.

DR: If there is a problem with me understanding what you created in your mind, is that your problem, my problem or both our problems?

WC: If I was obscure or ambiguous, it would be my problem. But I was, repetitititititively, quite specific.

DR: Surely, my difficulty in understanding what you invented doesn't change what happened in the delivery room!

WC: The weight of the baby will change over time, the symbol will not. You may perhaps not like my symbol and would use another one. That is fine with me, as long as we make it clear for each other that these symbols denote the weight of THAT baby, not the magnitude of THAT baby's weight.

Thus, again, I use the symbol ONLY for THAT baby's weight, not for any other baby's weight. I made that quite clear, but you ignore it, and I am interested in knowing why you ignore it. I repeat thus about that symbol: "The numbers are there to differentiate that baby's weight from some other baby's weight."

DR: I am happy to be corrected on what you meant to say. Can you explain how I know how to figure out the baby's identity and the name of the force of attraction (not the magnitude of the force as you suggest) from the symbol #w-1234?

WC: Excuse me ? Do you not know how a baby looks like ? If I am in a delivery room, and they ask me to take the weight of that baby, I don't think I would grasp some bucket and measure its diameter. Or do you mean literally what the name is of that baby? I don't see what that has to do with that baby's weight. It has to do of course with putting the value in the right record. But again, that adds nothing here to the discussion.

DR: Symbol #w-1234 has common name: "weight"

WC: No! that symbol denotes the weight of THAT baby. The symbol itself certainly does not have the common name "weight". It might be given the common name "symbol" though. You can use the common name "weight" to denote that baby's weight, but that is imprecise and may lead to exactly the sort of confusions that you exhibit.

DR: I can agree to narrowing down my understanding of #w-1234 if you can teach me how to make sure the symbol unambiguously represents the baby's identity and other things that affect the force of attraction between the baby and the earth.

WC: Because I told you. "#w-1234" is the symbol that I use to denote that baby's weight. If you were there, I would have pointed to the baby. If not, I could show you a picture, or you would get other information related to the parents, etc. All that information could be put in some symbol dictionary or look-up table. And no, the idea is NOT to infer it from the form of the symbol itself. I think that the notion of no meaning IN the code is broadly accepted.

DR: Symbol #w-1234 has definition: "the force of attraction between the baby's molecules and the earth at that location and at that point in time

Symbol #w-1234 "has location: delivery room "latitude-longitude-altitude"

Symbol #w-1234 has time: TS

Symbol #w-1234 has baby: identity of baby

WC: No ! I did not give a definition. And if I would have done so, it would have been a quite different one.

DR: Since a physicist, or a physician, would give the definition I inferred from your use case, which would you supply?

WC: That is irrelevant in this case. We are talking about the simple notion of weight.

DR: Once the symbol "#w-1234" is created in Werner's mind and written down and re-created in my mind ...

WC: The symbol is on some bearer medium. Whatever happens in my brain is irrelevant here. The symbol is for sure not "created" there. Something will happen there, of course, some state of affairs involving neurons and neuro-transmitters and so forth, and there is some relationship between the symbol on the medium and the state of affairs in my brain. If I would wish to say something about that particular state, I would use another symbol for that. At that point, I could imagine that you would say: "Ah, you see, you assign another symbol to that symbol", but if you did, then clearly you did not get the point.

DR: We can communicate using the symbol.

WC: Right, and independently of whatever our brain does in this case, because we agreed (I hope, finally) that we use "#w-1234" ONLY to refer in descriptions to THAT baby's weight (NOT its magnitude, NOT the act of measuring in order to determine this magnitude, ...)

DR: However, the weight is still the force of attraction between the baby's molecules and the earth.

WC: probably, but irrelevant.

DR: Not irrelevant to me, because the force of attraction, the earth, the baby, the people like you and me, are the only things really existing in my reality. Everything else is made up in your mind. What is in your mind is important to me, but I don't confuse what is in your mind with my reality.


DR: When you say "obtain a value for the baby's weight, for which I have to do a measurement" you add a new attribute to the symbol for weight: "value"

WC: no ! In the sentence above, I didn't mention or introduce another symbol at all. The symbols I introduced were:
#w-1234 : THAT baby's weight
#m-5678 : THAT process (which occurred during THAT time) of measuring THAT baby's weight
4.7 kg : the value obtained for THAT baby's weight through THAT process
#r-881 : the process of entering the obtained value in some record
I did not introduce the symbol "value".

DR: Your whole paragraph is made up of symbols. Above, you just pick out several symbols from the paragraph and throw away the rest.

WC: Try not to confuse the readers by throwing in another level of symbols. I was quite specific about what the symbols I was talking about are. All, except the "4.7 kg" started explicitly with #.

DR: In any case, I now see you added to your story the term "process".

WC: ... in a humble attempt to make you see the difference between (1) what is to be measured, (2) measuring itself, (3) and the value obtained through the measuring.

DR: ... and defined 2 processes:

1) #m-5678 : THAT process (which occurred during that time) of measuring THAT baby's weight
2) #r-881 : the process of entering the obtained value in some record

WC: I didn't define these processes. In the scenario, these are two processes which are relevant to our discussion (because you confused them) and for which I introduced two different symbols.

DR: It is helpful for me to know that you feel these are two processes, which represent the movement between three states. Thank you for the extra detail. In my mind, that communicates the standard state transition model where process describes the movement from state to state.

WC: I am not responsible for the limitations in your language of choice, i.e. the standard language of state transition models. If you don't get the right results by using that state transition stuff when addressing this scenario, then don't blame me; blame your language.

State 1: pre-condition to Process #1
Process #1: #m-5678 : THAT process (which occurred during that time)of measuring THAT baby's weight

4.7 kg : the value obtained for THATbaby's weight through THAT process
State 2 is both the post-condition of Process #1 and the pre-condition to Process #2
Process #2: #r-881 : the process of entering the obtained value in some record
State 3: is the post-condition of Process #2.

DR: You said, "When I want to register something about that particular measurement, I will use the symbol #m-5678".

Here you identify the measurement with a symbol and fill in the value with a symbol:
#m-5678{symbol #w-1234
has common name: "weight"
has definition: "the force of attraction between the baby's molecules and the earth at that location and at that point in time ...
The act of measurement, which gives a magnitude which in this case is something that we have been taught to register as '4.7 kg' , he identifies with the symbol
has location: delivery room "latitude-longitude-altitude"
has time: TS
has baby: identity of baby
measurer: Werner
value: #r-881
WC: No ! Again, you confuse the measurement (the act of measuring) with the weight of the baby. It is for THAT measurement act, that was performed to get a value for THAT baby's weight, that I use the symbol "#m-5678". I can then use that symbol to document, for instance, that the measuring act took 55 seconds to perform.

Furthermore, I didn't fill in any value.

Furthermore, you erroneously equate #r-881 with that weight, which I clearly (or so I thought) explained r-881 to be the act of registering the obtained value in a record. I wrote that:
The measurement gives me a magnitude which in this case is something that we have been taught to register as '4.7 kg'". Now that act of registering (entering "4.7" into a computer, for instance) is an act in its own right, and when I want to refer to that act, I use the symbol #r-881 (you get the picture, I hope).
But clearly, you didn't get the picture, confusing now THREE things.

DR: I must apologize for not clearly discovering what is in your mind. Again, is that my problem or our problem? If what you want to achieve is good communication, you have to be very clear for those of us who can't read your mind.

WC: You didn't have to read my mind. You only had to read what appeared on your screen after opening my message. Again, if you are not able to distinguish the symbols that I introduced from the natural language that I used to try to describe to you what they stand for, then suggest a better language.

DR: I see from your explanation of process above, that you meant to use the symbol "#r-881" to represent "the process of entering the obtained value in some record".

WC: Yes !!!!!!!! Great !!!!!!!!!

DR: ... and not the magnitude of the force of attraction. I would ask however, other than communicating the symbol"#r-881," what gets communicated along with the symbol in process #2, the process of entering the value in the record?

WC: I didn't say anything about that, as yet. But stuff that might go there is, for example, how long it takes to enter weight values in a record (interesting for comparing user interfaces from an ergonomic and effort required perspective) or who entered the data (that gives you the culprit in case of mistyping) or when the data was entered (the weight was taken at time t, but the registration at t+1).

DR: Summary: I believe these are the symbols you assigned in your own mind and communicated in your paragraph.

WC: As I explained above, your belief is wrong.

DR: Here is how I created the communication in my mind and communicated it back -- is my creation in my mind wrong from your point of view?

WC: yes, indeed. You confused several different entities.


Act.ii = #m-5678
Act.code = "3-1234 (weight--the force of attraction between the baby's molecules and the earth at that location and at that point in time)
Act.effectiveTime = TSAct.observation.value = #r-881
Act.participantMeasurer = Werner
EntityPatientRole = identity of baby
Entity.location = "latitude-longitude-altitude"

WC: On the basis of what I described above, you must identify at least 2 acts in HL7-speak, and not just one as you came up with: one is for measuring the weight of that baby, the other for registering the value obtained through the former in a record. Furthermore, there must be at least three non-act entities: the baby, its weight and the magnitude of this weight at the time of the measurement (i.e., first act). Now I can accept that this detail is not relevant for many purposes and that therefore you don't want to register these things (although then I don't understand why you consider the baby's molecules and the gravity of the earth to be of relevance here - and please, don't take the latter statement as an indication that I don't know what weight physically is about, it is simply irrelevant). But you should NOT come up with a representation as you did - in HL7-speak, I believe - that CONFUSES the different elements.

Compare with this analogy: if you take a picture of some scene (say of your best friend and his wife), and parts of the scene are irrelevant (say his wife), you can cut out these parts of the picture. The remaining parts (the picture of your friend) still depict faithfully the corresponding parts of the scene. One should not, in contrast, use some analogous technique of removing irrelevant parts if this means that the relevant parts will get distorted as well.

Your analysis of my use case was clearly wrong: I pointed out precisely where you went off track. The $60M question is now: WHY ? I can come up with several possibilities, but prefer, as Anthony asked and we agreed to, to keep the discussion germane to the issue. Thus I argue here (as before and as a few others have done earlier) that the semiotic and speech act theories and architecture of the "HL7-language" are such that they mislead even experts like you: HL7, in many cases, lets you build representations which are such that removing irrelevant detail leads to distortion of what is relevant.

DR: Certainly, I have learned more about how your mind works in this exchange.

WC: Sure ?

DR: That is important because as I communicate back to you what I heard from you, I make misinterpretations unless your language is VERY clear.

WC: Wasn't it ? I think the problem is that from the very beginning you lumped different things together. As you know, getting things-lumped-together apart is harder than lumping things together. Third time: propose me a more formal language then.

DR: Of course, our communication patterns don't change what happens in the delivery room, and we have to decide why we are bothering to communicate if it doesn't change what happens in the delivery room!

WC: I don't get your point.

DR: Perhaps you can try again to make clearer language, and we can see if you succeed in getting a more accurate return communication. I've given you some hints of how my mind works such that you can craft a more understandable version for my brain.

WC: It seems, as I indicated above, that you cannot make, or do not wish to make, links from what is IN language, to what it is in reality which the language is ABOUT. I guess that is the brain-washing effect of HL7.


Sam said...

Hi All,
Someone has pointed me to this discussion regarding an openEHR view of the content. First lets remind ourselves of the key aspects that Werner wants to capture:

#w-1234 : THAT baby's weight

The first thing is to identify that baby (it may be that it is a multiple birth) so the subject of data may have to be identified in some way (1234). The fact that it is a weight is represented by the choice of archetype (weight).

#m-5678 : THAT process (which occurred during THAT time) of measuring THAT baby's weight

The information about the process of measuring is recorded in the protocol, and the event that is associated with the value. Here it will be a point in time to represent the particular measurement.

4.7 kg : the value obtained for THAT baby's weight through THAT process

This is the value associated with the event of measurement.

#r-881 : the process of entering the obtained value in some record

This is the commital process of that data and is identified at that level.

Werner is pointing out the context issues to have a full grip on the information. Although his 'map' does not match the usual clinical recording process in some ways, he has some of the context here. We could add information about the device, about the timing and measurer, the author of the document, the date of commital of the document, the date the document arrived in this health record...etc, etc

Adrian said...

The real issue is of course, that kg is the unit of mass, not weight!

If you want to record the weight of the baby, you should be using Newtons, the unit of force!

Pedantic humour aside, this reminds me of a compromise made in an HL7 message specification forced by supplier pressure.

The supplier uses some "magic numbers" to denote special circumstances (like "unknown"). Despite HL7 v3 having "null flavours" which covered all the possible circumstances covered by the magic numbers (and then some!), the supplier refused to allow these to be used. I presume that the prospect of working null flavour mappings into their system was just too distasteful. Instead, a textual note appears in the documentation of the HL7 message as to what those magic numbers mean.

Now, one of the purposes of HL7 v3 (as I understand it) is that you should be able to read a message in isolation and get an understanding of what it means (ignoring the fact that your brain may explode). Using magic numbers where there are standard alternatives defeats this, of course. Instead, you may get someone phoning the Guinness book of records to report that a 9999 gram baby has just been born. And that the force of gravity exerts 98.0567N of pull on them (at sea level).

Anonymous said...

That is one mind boggling exchange. WC has the patience of a god. DR is a religious fanatic. DC is into some powerful mojo. Every HL7 consultant team should include a witch doctor.