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The NNF does not include class disjointness, transitive properties, reflexive properties and sufficient conditions represented as General Concept Inclusions (GCIs) in the OWL axiom refset.

Inferred relationships for concrete values, e.g. decimal, integer, string, or dateTime, should be included in a separate relationship file.

Rules for Determining Redundant Relationships

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Example for Class inclusion

Stated relationships

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Inferred relationships before the removal of redundant relationshiprelationships

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Inferred relationships after the reduction

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For

Example in OWL axiom refset and RF2 relationship file (NNF)

Example for Role inclusion

Stated relationships

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Inferred relationships before the removal of redundant relationship

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Inferred relationships after reduction

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For concept

Example in OWL axiom refset and RF2 relationship file (NNF)

Rule 2  - Property chains including transitive properties

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• Attribute u is the same as or a subtype of t, and

• D has a relationship to C via attribute s

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Example for property chain:

Stated relationships of

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Stated relationships

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of

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Inferred relationships before the removal of the redundant relationship

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Inferred relationships after the reduction

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For

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Example in OWL axiom refset and RF2 relationship file (NNF)

Technical Implementation for Calculating the NNF

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1. Read the Stated Form from RF2 files.

1. The following files are required: Concept, Stated Relationship, OWL Ontology Reference Set, OWL Axiom Reference Set. 

2. If the edition has any active stated relationships then the Stated Relationship and MRCM Attribute Domain Reference Set files are also required.

2. Use the OWL API to infer the class hierarchy

1. Build the Ontology object using:

1. Axioms from the OWL Axiom Reference Set, making a note of any Transitive property and Property Chain axioms.

2. Axioms created by converting Stated Relationships to OWL Axioms using the MRCM Attribute Domain Reference Set for list of attributes which should not be grouped in the given domain.

2. Use a reasoner to pre-compute the class hierarchy.

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Calculating the necessary normal form happens in two passes of the hierarchy.org.snomed.otf.owltoolkit.normalform

1. Walk the class hierarchy in a top-down, breadth first, order.

1. For each class visited gather the stated attributes of this class and each inferred parent.

2. Compare the attributes and remove those which are found to be redundant because they are less specific in terms of depth in the hierarchy.

3. During this first pass build a hierarchy for property chains and transitive properties.

2. Walk the class hierarchy again in the same order reducing the attributes of each class further.

1. Compare the attributes and remove those which are found to be redundant because they are less specific in terms of depth in one of the alternate hierarchies.

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1. All 

   Concept
   t 116680003 |Is a|

    relationships should be assigned in role group 0;

2. Attribute that is not grouped, not a value of 

   Concept
   ShowParts term t 609096000 |Role group (attribute)|

    or grouped=0 in MRCM, should be assigned in role group 0;

3. Attribute that is grouped, value of 

   Concept
   ShowParts term t 609096000 |Role group (attribute)|

    or grouped=1 in MRCM, should be assigned in a role group 1 or abovenumber that is not 0. Each 

   Concept
   ShowParts term t 609096000 |Role group (attribute)|

    in the OWL axiom should be presented by a unique role group number. Note, role group merging is not covered here.

An example for the current diagram representation for attribute in role group 0 in the stated relationship file and concept model diagram

After the complete OWL axiom refset is implemented,

Representation of