Requirements

In this page, we state the requirements of SNOMED CT Compositional Grammar. These requirements are grouped into General SNOMED CT Language Requirements , which are shared by all SNOMED computable languages, and Representation of Clinical Meaning Requirements, which enable the representation of clinical meanings in health records, messages or expression associations.

General SNOMED CT Language Requirements

The general SNOMED CT language requirements include:

Requirement G.1 : Backward compatibility

The language must be backwardly compatible with any version of the language that has previously been adopted as an SNOMED International standard. This means that any expression that is valid based on the previous SNOMED CT Compositional Grammar standard

1 should also be valid based on this updated version. Please note that this requirement does not preclude extensions to the language which do not affect its backward compatibility.

Requirement G.2 : Consistency

Each logical feature of the language should have a single, consistent meaning across all SNOMED computable languages. Each logical feature should also have a consistent set of syntax representations.

Requirement G.3 : Sufficient and necessary

Each language must be sufficiently expressive to meet the requirements defined for the use cases it was designed for. However, functionality without a corresponding use case will not be included, as this increases the complexity of implementation unnecessarily.

Requirement G.4 : Machine processability

In order to facilitate the easy adoption by technical audiences, instances of each language must be able to be parsed into a logical representation using a machine processable syntax specification. This requirement will be met by defining the language syntax in ABNF.

Requirement G.5 : Human readability

Non-technical stakeholders require that the language is as human readable as possible, while still meeting the other requirements. This is essential for both the clinical validation of expressions, as well as for the education and training required to author expressions.

Representation of Clinical Meanings

The requirements for representing postcoordinated clinical meanings in health records, messages and expression associations are:

Requirement M1: Unambiguous meaning

An expression must be able to specify one unambiguous meaning, independently of the implementation environment.

Requirement M2: Conformance to concept model

Expressions must conform to the rules defined by the SNOMED CT concept model, or be transformable into an expression that conforms to the SNOMED CT concept model. For example, expressions with a clinical finding that is refined using the attribute 272741003 | Laterality| , can be transformed into a conformant expression by applying the laterality to every lateralizable body structure within the definition of the clinical finding. Please note that expressions may either conform to the international SNOMED CT concept model, or a local (e.g. national) extension to the concept model.

Requirement M3: Subset of SNOMED CT's Description Logic profile

The logical features provided by SNOMED CT compositional grammar must be a subset of those supported by SNOMED CT's Description Logic profile. This profile is primarily based on OWL 2 EL, however some additional features (which are still able to be classified in polynomial time) may also be included. This ensures that all clinical meanings expressed using SNOMED CT compositional grammar can be translated into an equivalent representation in OWL and classified in polynomial time.

Requirement M4: Functional requirements

The logical model must support the following capabilities:

Function	Details
Concept reference	The ability to reference a precoordinated SNOMED CT concept using its identifier and optional human-readable term.
Intersection / Conjunction	The ability to connect two focus concepts via a logical AND operator.
Refinement	The ability to refine (or specialise) the meaning of an expression using one or more attributes values.
Attribute group	The ability to group a collection of attributes which operate together as part of a refinement.
Attribute	An attribute-value pair which further refines the meaning of the expression
Nesting	The ability to include an expression as the value of an attribute
Concrete values	The ability to use integers, decimals, strings and booleans as attribute values
Definition status	The ability to specify whether the clinical meaning is 'equivalent to' or a 'subtype of' the expression.