Earlier in the projects history it was decided not to use role groups for the Observables model, mainly because at the time, the model was proposed to include nested definitions more specific than what role grouping admits. Also, the nesting patterns using role groups for procedures and findings (i.e. having more than one "part" of the procedure or more than one "condition" for the finding) does not apply to observables. There will only ever be one kind of quality and observation procedure referred to by one observable.
Below is an example of the relationship table for an observable created using SnoOwl from UNMC:
| id | effectiveTime | active | moduleId | sourceId | destinationId | relationshipGroup | typeId | characteristicTypeId | modifierId |
| 389446341000004000 | 1 | 900000000000207000 | 799635351000004000 | 117362005 | 0 | 370132008 | 900000000000225000 | 900000000000451000 | |
| 154043481000004000 | 1 | 900000000000207000 | 799635351000004000 | 64195000 | 0 | 704320005 | 900000000000011000 | 900000000000451000 | |
| 113689121000004000 | 1 | 900000000000207000 | 799635351000004000 | 443412009 | 0 | 116680003 | 900000000000011000 | 900000000000451000 | |
| 953865841000004000 | 1 | 900000000000207000 | 799635351000004000 | 367651003 | 0 | 704319004 | 900000000000011000 | 900000000000451000 | |
| 978593911000004000 | 1 | 900000000000207000 | 799635351000004000 | 441652008 | 0 | 704327008 | 900000000000011000 | 900000000000451000 | |
| 326682591000004000 | 1 | 900000000000207000 | 799635351000004000 | 776042991000004000 | 0 | 9216841000004100 | 900000000000011000 | 900000000000451000 | |
| 557253841000004000 | 1 | 900000000000207000 | 799635351000004000 | 118536000 | 0 | 704318007 | 900000000000011000 | 900000000000451000 | |
| 326573721000004000 | 1 | 900000000000207000 | 799635351000004000 | 123029007 | 0 | 370134009 | 900000000000011000 | 900000000000451000 | |
| 232992231000004000 | 1 | 900000000000207000 | 799635351000004000 | 258066000 | 0 | 246501002 | 900000000000011000 | 900000000000451000 |
As can be seen, all relationship groups (role groups) are 0. Most attributes use to define observables are exclusive to the observables model, with the exception of 246093002 | Component (attribute) |. The same SnoOwl tool outputs observables concepts as below:
The RF2-to-OWL script provided with the international release of SNOMED CT role groups everything that isn't explicitly marked as "never grouped" by hard coding the list of attributes not to be "automagically" put into role groups. All other attributes are currently put inside a role group, even if relationshipGroup equals 0 in the RF2 file. Currently these "never grouped" attributes are:
$nevergrouped{"123005000"} = "T"; # part-of is never grouped
$nevergrouped{"272741003"} = "T"; # laterality is never grouped
$nevergrouped{"127489000"} = "T"; # has-active-ingredient is never grouped
$nevergrouped{"411116001"} = "T"; # has-dose-form is never grouped
There are three possible solutions:
- Always role group all observables into one group. + easy to achieve, - no straightforward corresponding semantics (as for findings and procedures)
- Make observables use two role groups, one for target of observation (quality, disposition, function) and one for the observation procedure, + almost as easy, - interim solution
- Create a new COMPONENT-like attribute exclusive to the observables model and add all observables attributes to the "never grouped" list. + easy to achieve (see David Sperzel's comment), - lack of re-use between models (procedures and observables)
- Remove role groups from evaluation procedures (which should be observables anyway?), - more invasive solution (~9000 concepts, 15 with explicit role group)
- Add rules to OWL generation software (or similar) which distinguishes between observables and procedures