Incomplete Static Models

Introduction

In order to use static models for templates, we need to be able to have incomplete static models. An incomplete static model is a model that leaves some content open.

Rationale

Usually a static model is complete - any content not described by the model is disallowed. For normal static models - D-MIMs, R-MIMs, CMETs - this makes complete sense. But when it comes to templates, such completeness is often not appropriate.

A typical case is the use case for a template that says that this observation must have a snomed code associated with it. A simple static model would therefore have a single Act Class, with classCode <= OBS, and a constraint on the code to say that there must be a term from snomed.

(It's not the focus of this page, but assuming that the oid for the snomed code system is [snomed_oid], then the constraint might look something like this in OCL:

 inv: code->hasCodeSystem([snomed_oid])

This fragment depends on some decorations on CD, but that's not what this page is about)

The problem with the simple static model described above is that it says that the observation cannot have anything else on it - only a classCode and a code, and no associations. Not very useful.

An alternative is to add every attribute, and also to add every possible association. This includes all the classes that might be encountered, including at the very least the entire RIM backbone - but this is all getting very difficult. At the least we can say that the conceptual problems this brings up can be ignored since no one would ever bother writing such a template for a simple statement.

The solution to this is to allow a static model to say somethings, and refrain from making rules about some content. This is known as an incomplete static model.

Maximum and Minimum Models

The first option that we (LM,GG) considered was maximum and minimum models. This is a concept that is used with stubs to describe what possible models can be bound to the stub. The model that is bound must be between the two models, minimum and maximum.

This concept works when a model is compared to minimum and maximum models (at least for some usages), but doesn't work with instances. It's relatively easy to figure out how cardinality works with minimum and maximum models, but fixed values is a problem. If you tried to capture the case above using a min/max approach, it turns out the min model is irrelevant, and the max model must make the rule - and it turns out to be the same model as the full model with the backbone etc above.

So this is not useful.

Incomplete Classes

A workable approach is to add a flag to classes in static models. The flag on the class is called "incomplete". If this is flag is set, then any attributes and associations that are not mentioned are not constrained in any fashion. Any attributes or associations that are defined carry the normal meaning.

The default value for the flag is false - classes are always complete by default.

This flag can only be set to true in a LIM. If a model is to be used as a CMET, Message, Document etc, then the flag must be false. (All sorts of problems if you tried to allow incompleteness in these kinds of artifacts).

To prohibit an attribute in an incomplete class, set the cardinality to [0..0]? You cannot prohibit an attribute if it is mandatory in the model from which this is derived, of course.

Like attributes, associations are prohibited by setting the cardinality to [0..0]. Since associations are not distinguished by name, but by their data content (at least not when used as templates), what is prohibited is the existence of any association that meets the criteria specified by the constraints on the class that the association points to.

Methodology consequences

Diagrams

The flag will be shown on the model as a ? (bright purple border? snazzy picture?)

The flag will be shown as the text "Incomplete" in italics and bold in the table views.

The flag will be stored in the MIF as a boolean attribute with a default value of false on the Class type.

Examples

Use snomed codes

This example is based on the use case discussed in the introduction to this document. Making this into a template:

• define a static model with a single class.
• Set the incomplete flag to true
• set the classCode <= OBS
• add the snomed constraint from above (inv: code->hasCodeSystem([snomed_oid]))
• leave all the other attributes off.

Outstanding issues

Entry points.