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RE: [mdt-sbvr.dev] 3rd set of comments on MRV

I inserted a few comments like this, prefixed with "Mark:"
--------------------------------
Mark H. Linehan
STSM, Model Driven Business Transformation
IBM Research

phone: (914) 945-1038 or IBM tieline 862-1038
internet: mlinehan@xxxxxxxxxx
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RE: [mdt-sbvr.dev] 3rd set of comments on MRV

I’ve replied like this, marked “Stan:”

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RE: [mdt-sbvr.dev] 3rd set of comments on MRV

I added yet more, like this. I prefixed mine with "Mark:" to make it clearer.
--------------------------------
Mark H. Linehan
STSM, Model Driven Business Transformation
IBM Research

phone: (914) 945-1038 or IBM tieline 862-1038
internet: mlinehan@xxxxxxxxxx
Inactive hide details for "Stan Hendryx" <stan@xxxxxxxxxxxxxxxx>"Stan Hendryx" <stan@xxxxxxxxxxxxxxxx>

                  "Stan Hendryx" <stan@xxxxxxxxxxxxxxxx>
                  Sent by: mdt-sbvr.dev-bounces@xxxxxxxxxxx

                  11/21/2008 12:56 PM

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SBVR developer list <mdt-sbvr.dev@xxxxxxxxxxx>
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RE: [mdt-sbvr.dev] 3rd set of comments on MRV



Mark,


I’ve added some more in this pen.


Stan

Stan, thanks for your comments. I added my own in this pen.
--------------------------------
Mark H. Linehan
STSM, Model Driven Business Transformation
IBM Research


Mark,

Please see comments inline below.

Stan

Mark Linehan wrote:

* Most of LFSV is missing. In particular, AtomicFormulation and RoleBinding are not implemented -- and I can't model something as simple as "Driver Bill has age 35" without those.

Right. LFSV is needed to create semantic formulations.

My question is: what is the status of this. I someone planning to finish LFSV?

MDT-SBVR can focus on MRV and get it to work to interchange fact models and conceptual schemas with concepts, definitions, namespaces, etc., without having to involve LFSV. We can also do VDBV then VDBR after MRV without having to do LFSV. LFSV can be done any time after MRV. SBVR is last of all. See SBVR Fig. 2.1, p.4. This is a logical roadmap for MDT-SBVR, with usable milestones at each compliance point. In any case, I think we should get MRV to work before tackling any of the other SBVR vocabularies.

Mark: I am specifically interested in the AtomicFormulation part of LFSV in order to enable Actualities such as "driver Bill has car A". I have been experimenting with such modeling in order to understand the characteristics of the design when applied to individual concepts and instances.

Stan: Right. I understand. Sentences formulated as a single atomic formulation with no logical operations or quantifiers is an important subset of LFSV. These can be directly related to a particular row and column in a relational table, e.g. Driver Car
Bill A
Stan B

The values are literals that satisfy a reference scheme for the concept at the head of the column, i.e. are identifiers.

Mark: yes, but your reference to a "relational table" is a little confusing. It seems to me that an AtomicFormulation can avoid using quantified variables only be referencing IndividualConstants and/or Expressions. As soon as you want an AtomicFormulation to reference instances in a relational table, you must use quantified variables for the references.

* Since a Text is a kind of _expression_, which is a kind of BindableTarget, I can see how the string "Bill", instantiated as a Text, can participate in an AtomicFormulation. But I don't see how a boolean true/false value or a number can be a BindableTarget. For example "Driver Bill is of age" and "Driver Bill has age 35". I think this is a problem with the SBVR spec. Comments?

A variable can be a bindable target, and the variable can range over propositions (which are true or false) or numbers.

I retract the above sentence. It is false. I’m not sure what I was thinking when I wrote it! A variable can range over any kind of concept, including a fact type. In SBVR, integers have values that designate them; see 13.2.7, p.187. Similarly with text. Numbers other than integers are not defined in SBVR; they need to be in a model. For example, real numbers, rational numbers, complex numbers. ISO 6093 Number Namespace gives designations for real numbers.

An individual concept can be a bindable target, too. One would typically bind to the individual concept designated by “Bill” rather than the _expression_ “Bill” in an atomic formulation.

My model contains a fact type "Driver has Name". (Note that I am not using the clause 11 "name" concept, but instead a model-defined concept.) To model "IndividualConcept of Driver has name Bill", I create an IndividualConcept of "Driver" and I want to build an AtomicFormulation that binds to (1) the IndividualConcept, and (2) the Text "Bill". This is possible because SBVR clause 9.2.1 says a a BindableTarget can be a Variable, an _expression_, or an IndividualConcept.

I would think that “driver” is an object type, not an individual concept, and that “Bill” designates an individual concept that specializes “driver.” You seem to do this in the paragraph below.

Mark: yes, a "driver" is an object type. I am "an IndividualConcept of "Driver"". I don't bother with the clause 11 "name" concept but instead have a fact type "driver has name" to identify a model-specific "name" concept associated with the "driver" concept.

Stan: This highlights a difference between the use of an individual concept of a general concept and a reference scheme for the general concept. If {name} is a reference scheme for “driver”, then existential facts of different drivers can be instantiated without the need to individually conceptualize each:

Driver Table
name:
Bill
Mark
Stan

A thing only needs to be individually conceptualized if it needs to be distinguished and is in a conceptual schema. Then, it can play a role in fact types, like any other concept. For example, EU-Rent might include the individual concept designated by “EU-Rent” in its conceptual schema as a distinguished thing in order to formulate fact types that are unique to it, or refer to it by its designation in the schema without having to have an associated “name” fact type role.

Mark: yes. But I am trying to do something else, and the use of the role name "name" is confusing. Try a different example, such as "Driver has Title" where "Title" has "General Concept: String". Clearly, I can have an AtomicFormulation for "Driver Bill has Title 'chauffeur'", where "Bill" is an IndividualConcept of "Driver".

Now consider another example, "Bill has age 35. By analogy with the previous example, I would expect to create an AtomicFormulation based on the FactType "driver has age", with bindings to the IndividualConcept "Bill" and the Number "35". But I can't do that because a Number is not a BindableTarget.

However, there can be a variable that ranges over “age,” where an age is the duration since birth, with any fractional year of the duration truncated. A literal value of “duration” is a quantity value, consisting of a number and a measurement unit, as “Bill has age 35 years.”

Mark: This is not very satisfactory. (a) I don't think I should have to extend my model to say that "age is the duration since birth" in order to express the number, if I don't find it valuable to me; (b) if I did this, it still doesn't answer how I would bind the number "35" to the number part of the quantity value.

Stan: In any fact model, what kind of thing “age” is depends on the conceptual schema of the fact model. If you defined “age” as a specialization of “number,” then you can refer to an age by providing an _expression_ for a number, like “35” or “XXXV”. It would then require exogenous information to determine what “35” means, absent a measurement unit in the schema. If you were using our date-time vocabulary as part of the conceptual schema, you would probably say that an age is a duration since birth or creation, and use quantity values as literals.

Mark: you propose an AtomicFormulation based on "driver has age" (where "age" has "General Concept: number") that binds "Bill" (an IndividualConcept of "Driver") and "35" or "XXXV". But SBVR has nothing that indicates how to interpret such an _expression_. For example, is "XXXV" really legitimate?

Mark: How about we assume that a number such as "35" is an IndividualConstant of type Number, with its name set to the corresponding numeric value? This is justified by this sentence at the top of page 90 in the spec: "Trivially, each fact model includes existential facts to declare the existence of generic constants such as numbers, ...."

Stan: No need to introduce IndividualConstant. SBVR effectively does this by providing for a value attribute in the XML for “number”. See SBVR 13.2.7 Data Values, p.187.

Mark: The example in 13.3 uses a number value only for the numeric part of "... at least 3 officers." The main part of the SBVR specification does not sanction binding a number as an _expression_.

It's even worse for an example involving a boolean value such as "Bill is of age". I want to create an AtomicFormulation based on the FactType "Driver is of age". I can bind the only role of the FactType to the IndividualConcept "Bill". But what do I do about the truth value? There's no way (in SBVR) to specify a boolean value and no way to plug it into the AtomicFormulation.

You assert that Bill is of age by binding the individual concept designated by “Bill” to the role of the characteristic designated by “is of age.” This action instantiates the fact type. The instance is a fact. There is no need to deal with the truth value explicitly. The truth value “true” is implicit in the fact.

Mark: ok. Then I suppose that you specify that "Bill is not of age" by applying a "logical not" operation to the AtomicFormulation. Is that right?

Stan: Yes.

This example highlights a compromise that is made when mapping unary fact types to UML, needed because UML does not support unary associations. The preferred mapping of a unary fact type, or characteristic, to UML is as a Boolean attribute. However, the semantics are not exactly the same, because SBVR is open world and UML is closed world. In SBVR, failure to assert a fact does not mean that the fact is false; it means it is unknown whether the fact is true or false. (SBVR can “close” particular concepts, and “internally close” particular fact types as needed.) To handle this in UML and EMF, the mapped Boolean attribute should be allowed to be null (unless the SBVR concept is closed), representing “unknown,” and not be required to be either true or false. The SBVR XML either includes the characteristic, its negation, or neither. There is no need to use Boolean values in SBVR. See SBVR 13.2.3, p.184. See also 10.1.1.3, p.91ff.

Mark: EMF has a way to express that a value is not known: the set(), unset(), and isSet() methods.

Stan: Good! We should use these methods. There would be different rules if a concept is closed in a particular conceptual schema, than if it is not closed (the default in SBVR).

Regarding the point that "A variable can be a bindable target, and the variable can range over propositions (which are true or false) or numbers." -- I'm not sure how I would create a Quantification that ranges over the value "true" or over the number "35". And I believe that I shouldn't have to do that when I want to bind a literal value in an AtomicFormulation.

You don’t have to. Sorry for the confusion.

* I previously commented on the use of XPATH references (rather than UUIDs) between model elements. I think it should be possible to put these individual concepts in their own XML file, separate from the model file. But separating the individual concepts from the the model itself makes it likely that one will change independently of the other. Similarly, if one SBVR vocabulary incorporates another vocabulary, it is likely that they will be kept separately and evolve independently. XPATH references between separate vocabularies will be particularly brittle.

Unfortunately, “vocabulary” is in VDBV, not MRV. Use “namespace” instead of “vocabulary” with MRV, and put different namespaces in different files. Use “namespace has URI” and “namespace1 incorporates namespace2”.

OK. The MDT-SBVR MRV model currently has "Package" as a container for everything. I've previously asked how "Package" relates to "Namespace". I would be ok with eliminating "Package" and using "Namespace" as the container.

Uniqueness of designations and fact type forms in namespaces is used to identify terms, names, and fact types.

The current MDT-SBVR MRV design appears to use XPATH references. My complaint is that those are brittle. I'd be happy to have the XML file reference things via designations and fact type forms.

I agree.

If designations or fact type forms are changed in subsequent versions, references will break. To maintain upward compatibility between versions of namespaces, designations and fact type forms should not be deleted, but deprecated and replaced by other terms, if a new preferred synonym is desired. Also, definitions of a term should not be changed in a new version of a released namespace unless the new definition is logically equivalent to the old one, since the term will then refer to a different concept, with unpredictable results.

Sure, but (a) there are some changes that will not cause these types of breakages in principle, but will change XPATH references in practice. (b) during the period when vocabularies are under development, it should be possible to make such changes without technology-imposed problems.

Yes. Better to avoid the use of XPATH references, and stick with what SBVR does.

Mark: I think that some more development of the MRV model is needed to "stick with what SBVR does".

Stan: It sounds like it.

SBVR lacks a standard version control policy. Perhaps this project could establish some conventions to help manage this.

Let's get the EMF version of the metamodel done, first.

Right.

SBVR provides fact models and conceptual schemas to separate ground facts like “Driver Bill has age 35” from the schema in separate files. Each SBVR interchange file is a fact model, including fact models that may be used as conceptual schemas. Thus “conceptual schema” is a role of a fact model in another fact model. “Fact model has URI” and “conceptual schema has URI” are not included in SBVR, so there is no SBVR standard way to uniquely identify a fact model. It would be nice to have a URI for a fact model in the standard. I think “thing has URI” should be added to the spec to provide more flexible identification and reference of model elements, particularly for managing fact model modules.

Regarding the idea of adding URI's -- I would be ok with this. I suggest raising an issue on this point.

Regarding fact models and conceptual schemas -- I don't want to touch these until their relationship with namespaces, vocabularies, and the various other packaging concepts in SBVR are worked out.

I think MDT-SVR should not ignore “fact model” or “conceptual schema.” To conform to SBVR, MDT-SBVR must recognize “fact model” and “conceptual schema.” See SBVR 2.3, p.5. See also 10.1.1.2, p.86ff. A basic, usable, packaging arrangement is thus included in SBVR. Namespaces are well defined in relation to conceptual schemas. We don’t need to wait on resolving issues with “vocabulary” to use “fact model” or “conceptual schema”. Since every SBVR interchange file contains a fact model, “fact model” is often implicit. However, “fact model” needs to be used explicitly in order to specify meta data about a fact model, such as the Dublin Core meta data elements. “Conceptual schema” is needed to express closure conditions on concepts in conceptual schemas, as mentioned above, and to refer to a conceptual schema in a fact model. It is clear that a fact model consists of a set of (ground) facts and a conceptual schema. A conceptual schema consists of a set of concepts (whose designations are in namespaces) and a set of (schema) facts. It should be possible to include a conceptual schema in a fact model by reference. One thing that is missing from SBVR to do this is “fact model has URI” and “conceptual schema has URI.” A nuance is that “conceptual schema” is a role of a fact model in another fact model, via “fact model is based on conceptual schema.” Do you see anything else that needs to be worked out?

Mark: MDT-SBVR's version of MRV has both FactModel and ConceptualSchema. What's needed is guidance on how these relate to "Packages" and "namespaces". I disagree that "Namespaces are well defined in relation to conceptual schemas" -- I can't find anything in the spec that addresses that relationship. In any case, the fundamental problem is that clause 8 doesn't make clear what concept is the outer "container" for all the other clause 8 concepts. MDT-SBVR MRV has invented "Package" for that purpose, but that's a hack.

Stan: SBVR Clause 2.3 makes it clear that “fact model” is the outer logical container, since, as it says, “An exchange document that conforms to this specification (an “SBVR exchange document”) shall be an XML document [file] that represents a ‘fact model’ as defined in subclause 8.5. The fact model shall be based on the conceptual schema specified in subclause 13.5 - the “SBVR model of SBVR.”” As for the relationship between namespaces and conceptual schemas, these fact types come into play: designation is in namespace; fact type form is in namespace; concept has designation; fact type has fact type form; “fact type” specializes “concept”; conceptual schema includes concept; conceptual schema includes fact [so-called “schema fact”]; fact model is based on conceptual schema; fact model includes fact [so-called “ground fact”]. The concepts introduced by a conceptual schema are represented as instances of the concept “concept” or one of its specializations (the concept types). Each such instantiation is a fact in a interchange document (fact model). Thus it is seen that a conceptual schema is a fact model based on SBVR (or some chain of conceptual schemas that terminates in SBVR) and includes facts that instantiate “concept” plus other facts, “schema facts”, that stipulate the necessities, possibilities, permissions, and obligations of the domain modeled by the conceptual schema, i.e. the business rules of the conceptual schema. Any fact model that instantiates “concept” and is ultimately based on SBVR can be used as a conceptual schema.

Note that different conceptual schemas might have the same concepts but different schema facts, making their behavior quite different. This is where business rules come in in a very significant way. It is often desirable to split a conceptual schema into at least two parts, the concepts and the schema facts. Some of the schema facts might be dynamic, particularly the obligations and permissions (deontic rules), with frequent rule changes possible. Of course, changing a rule might invalidate a lot of data, requiring potentially massive data updates to bring a fact model (database) based on one version of the schema facts into consistency with the new version of the schema facts (just ask any DBA!).

Mark: This doesn't help much. Right now, the MRV model has a class called "Package" that is used as the container for everything in the model. Perhaps this should be "FactModel", since that is apparently supposed to be the outer element of an XML interchange file. (But notice that clause 13.5 doesn't have a "<FactModel>" XML element.) Or perhaps we should be using "ConceptualSchema" since facts about the existence of concepts apparently belong to conceptual schemas. I guess we could have a fact about a conceptual schema inside a fact model (??) Similarly, I guess we could have a fact about a namespace inside a fact model (??) The point is that different tool developers will guess differently if given no guidance.

* I noticed a class "Element" in MRV that isn't used anywhere, and doesn't even have a corresponding "impl" class. I think it should be dropped.

“Element” is not defined in SBVR, but is used in the fact type “set has element”, which is a synonymous form of “thing is in set”, 8.7, p.42. See also Fig. 8.9. I think “element” should be added to SBVR, rather than dropping “set has element,” since the latter is in the vernacular of technical people.

If we do that, then the relationship between "instance" and "element" should be clarified. An instance is an element of a set that is the extension of a a concept.

Yes.

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