# Transformation Level 0 At this level, the terminology server requires all submitted expressions to already be in valid classifiable form. This form is a syntactically valid *and* concept model compliant representation expression that can be directly used as input to the classifier, enabling expressions to be classified together with other SNOMED CT content. {% hint style="info" %} For more details on the Machine Readable Concept Model, please see [SNOMED CT Machine Readable Concept Model](https://docs.snomed.org/snomed-ct-specifications/snomed-ct-machine-readable-concept-model/). {% endhint %} ## Implementation Advice To enable postcoordination at Level 0, it is important that the system used to create the expressions supports any transformation needed to represent the expressions in their classifiable form. This may be enabled using one of the following techniques: * Form-based Creation * Expression Templates These techniques will support the creation of expressions that fully comply with the concept model rules and avoid some of the common mistakes created. For example using attributes that are incorrect for the domain or incorrectly grouped. ### Incorrect Attributes Consider the situation where the following expression is created to represent the meaning of a "Disorder of left lung": ``` === 19829001 |Disorder of lung (disorder)| : 272741003 |Laterality (attribute)| = 7771000 |Left (qualifier value)| ``` At level 0, this expression would *not* be accepted by the terminology server, because the MRCM only permits those concepts that are both within the `<< 91723000 |Anatomical structure (body structure)|` domain and also listed in the [723264001 |Lateralizable body structure reference set|](http://snomed.info/id/723264001) to be qualified using [272741003 |Laterality (attribute)|](http://snomed.info/id/272741003) . The focus concept of the expression is neither. As a result of this rule, the action required to make the expression classifiable, is to add a nested expression where the laterality is applied to the value of the [363698007 | Finding site (attribute)|](http://snomed.info/id/363698007) attribute that is part of the NNF for the same focus concept, [19829001 | Disorder of lung (disorder)|](http://snomed.info/id/19829001) , as follows: {% code overflow="wrap" %} ``` === 19829001 |Disorder of lung (disorder)| : { 363698007 |Finding site (attribute)| = ( 39607008 |Lung structure (body structure)| : 272741003 |Laterality (attribute)| = 7771000 |Left (qualifier value)| )} ``` {% endcode %} ### Incorrectly Grouped Attributes Consider the situation where the following expression is created to express the meaning of a "Procedure on left lung": {% code overflow="wrap" %} ``` === 71388002 |Procedure (procedure)| : 363704007 |Procedure site| = 44029006 |Left lung structure (body structure)| ``` {% endcode %} At level 0, this expression would *not* be accepted by the terminology server, because [363704007 | Procedure site (attribute)|](http://snomed.info/id/363704007) is specified as being 'grouped', which requires a role group to be explicitly stated. As a result of this rule, the action required to make the expression classifiable, is to place the attribute in a group, as follows: {% code overflow="wrap" %} ``` === 71388002 |Procedure (procedure)| : { 363704007 |Procedure site| = 44029006 |Left lung structure (body structure)| } ``` {% endcode %} ## Examples Terminology servers at level 0 will reject any expressions not conforming to the classifiable form. The table below provides examples of a set of expressions with an indication of their acceptability and potential issues at level 0.
ExpressionClassifiableIssues
372244006 |Malignant melanoma| : { 363698007 |Finding site| = 91775009 |Left shoulder| }

Yes


Although this expression complies with the concept model rules, the expression will not classify as probably desired, as a subtype of 188060000 |Malignant melanoma of shoulder (disorder)| The reason for this is that the stated group does not include the required attribute: 116676008 |Associated morphology (attribute)| = 1162635006 |Malignant melanoma (morphologic abnormality)|
=== 188060000 |Malignant melanoma of shoulder| : 272741003 |Laterality| = 7771000 |Left|NoAttribute 272741003 | Laterality| does not apply to the domain | Malignant melanoma of shoulder|
=== 372244006 |Malignant melanoma| : { 116676008 |Associated morphology| = 1162635006 |Malignant melanoma| ,
363698007 |Finding site| = 91775009 |Left shoulder| }		Yes
=== 372244006 |Malignant melanoma| : { 116676008 |Associated morphology| = 1162635006 |Malignant melanoma| ,
363698007 |Finding site| = ( 16982005 |Shoulder| : 272741003 |Laterality| = 7771000 |Left| )}		Yes
=== 372244006 |Malignant melanoma| : 363698007 |Finding site| =
( 16982005 |Shoulder| : 272741003 |Laterality| = 7771000 |Left| )		NoAttribute 363698007 | Finding site| should be in a group
=== 372244006 |Malignant melanoma| : 363698007 |Finding site| = 91775009 |Left shoulder|NoAttribute 363698007 | Finding site| should be in a group
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