SNOMED
Core Structures
2nd AAHA Software Vendors Summit – April 21, 2009
Terminology of Terminology
• Concept
• embodiment of a particular meaning
• Really a “virtual” element in the system
• The string in concepts table is a member of the related list of
descriptions.
• Description
• Any string used to represent a concept
• Relationship
• (in SNOMED) an object – attribute – value triple connecting
two concepts through an attribute
• Relationships in SNOMED are explicit rather than implicit (as
was the case in SNOMED III)
Terminology of Terminology
• Extension (valid)
• SNOMED content outside of SNOMED core but integrated
such that it can be queried as if it were part of SNOMED
core.
• An official extension is created by an organization that holds
a namespace identifier (more later).
• Subset
• A functional subset of SNOMED is a list of concepts
extracted from core, an extension or both to serve a defined
purpose.
• Navigational subset
• A SNOMED subset that includes adequate hierarchical
information to allow navigation (browsing).
SNOMED Core
•
Concepts Table
•
•
Descriptions Table
•
•
Each row in this table represents a medical concept.
Each row in this table specifies a term that can be applied to describe a single
clinical concept.
Relationships Table
•
Each row in this table specifies a relationship between two clinical concepts. The
nature of each relationship is represented using a special kind of clinical concept.
SNOMED Core
• A concept is described by the term (string) in 2-n
descriptions
• At least the Fully Specified Name (FSN) + Preferred
Term
• Each description refers to (only) 1 concept.
SNOMED Core
• A concept is the source of 1-n relationships (except the
root concept).
• A concept is the target of 1-n relationships.
• A concept represents the type of relationship.
• A relationship refers to 3 concepts: a source, a target,
and a relationship type.
Concepts Table Fields
Key Fields
ConceptId
The unique SNOMED Clinical Terms Identifier for this
Concept.
Data Fields
ConceptStatus
The status of a Concept indicates whether it is in active use
and, if not, indicates the reason for withdrawal from current
use.
FullySpecifiedName
A unique phrase that describes a Concept in a way that is
intended to be unambiguous.
CTV3ID
The Read Code for this Concept.
SNOMEDID
The current SNOMED identifier for this Concept.
IsPrimitive
Indicates whether a Concept is Primitive or Fully defined by
its current set of Defining characteristics.
Descriptions Table
Key Fields
DescriptionId
The unique SNOMED CT Identifier for this Description.
Data Fields
DescriptionStatus
The status of a Description indicates whether it is in active use and, if not,
indicates the reason for withdrawal from current use.
ConceptId
The unique SNOMED CT Identifier of the associated Concept. (Foreign key
to Concepts Table).
Term
The text of a Term used to describe the associated Concept.
InitialCapitalStatus
An indication of whether the capitalization status of the first character of the
Term is significant.
DescriptionType
An indication of whether the Term is the Fully Specified Name, Preferred
Term or Synonym for the Concept to which this Description applies.
LanguageCode
An indication of a Language or Dialect in which this Description is valid. The
language or dialect subset ultimately defines the descriptions for each
concept.
Concepts -> Descriptions
233604007
D2-0007F
Pneumonia (concept)
350049016
233604007
Pneumonia (Disorder)
3
621810017
233604007
Pneumonia
1
xxxxxx01x
233604007
Synonym in Core
2
xxxxxxyyy11x
233604007
Synonym in NAHLN Extension
2
xxxxxxzzz11x
233604007
Synonym In Local Extension
2
1 = “preferred” description (term) – preferred by SNOMED, perhaps not your users
2 = synonym (alternate)
3 = fully specified name
Component History Table (future use)
Key Fields
ComponentID
The unique SNOMED CT Identifier for the changed Component.
ReleaseVersion
The version of SNOMED CT in which this change was made.
Data Fields
ChangeType
An indication of the nature of the change.
Status
The status of this Component after the change.
Reason
An optional text Description of the reason for the change.
Historical Relationships
Key Fields
RelationshipId
The unique SNOMED CT Identifier of this Relationship.
Data Fields
ConceptId1
The unique SNOMED CT Identifier of the Concept which is the source of this Relationship.
RelationshipType
The unique SNOMED CT Identifier of the Concept which represents the type of relationship
between the related Concepts.
ConceptId2
The unique SNOMED CT Identifier of the Concept which is the target of this Relationship.
CharacteristicType
An indication of whether a Relationship specifies a defining characteristic of the source
Concept or a possible qualifying characteristic of that Concept.
Refinability
An indication of whether it is possible to refine the target Concept when this relationship is used
as a template for clinical data entry.
RelationshipGroup
An integer value that links together Relationships which are part of a logically associated
Relationship group.
Historical Relationships
• Allowed attribute values
•
•
•
•
•
•
SAME AS (redundant)
MAYBE A (ambiguous - 2 or more)
REPLACED BY (major changes)
WAS A (IS A no longer valid)
MOVED TO (namespace change)
MOVED FROM (namespace change)
Relationships Table
Key Fields
RelationshipId
The unique SNOMED CT Identifier of this Relationship.
Data Fields
ConceptId1
The unique SNOMED CT Identifier of the Concept which is the source of this Relationship.
RelationshipType
The unique SNOMED CT Identifier of the Concept which represents the type of
relationship between the related Concepts.
ConceptId2
The unique SNOMED CT Identifier of the Concept which is the target of this Relationship.
CharacteristicType
An indication of whether a Relationship specifies a defining characteristic of the source
Concept or a possible qualifying characteristic of that Concept.
Refinability
An indication of whether it is possible to refine the target Concept when this relationship is
used as a template for clinical data entry.
RelationshipGroup
An integer value that links together Relationships which are part of a logically associated
Relationship group.
Concept -> Relationship
Concepts Table
SCT ID
SNOMED ID
71620000 DD-13100
116676008 G-C504
72704001 M-12000
Concept Name
Fracture of Femur
Associated Morphology
Fracture (morphology)
Relationship Table
Concept ID
Relationship ID
Concept ID
71620000
116676008
72704001
SCTID
• The SCTID data type is a 64-bit integer,
which is subject to the following constraints:
• Only positive integer values are permitted.
• The minimum permitted value is 100,000 (6 digits)
• The maximum permitted value is
999,999,999,999,999,999 (18-digits).
• As result of rules for the partition-identifier and
check-digit, many integers within this range are
not valid SCTIDs.
SCTID
• The SCTID does not contain semantic information
related to the meaning of a concept or term
• It does however have a structure that is designed to
allow different types of terminological components to
be recognized.
• The nature of a component can be derived from the table in
which a component is distributed.
• Partitioning the SCTID avoids reuse of the same identifier for
a different type of component – thus avoiding ambiguity.
• This also allows the nature of the identifier to be recognized
when stored in a record or transferred in a message.
SCTID
SCTID for centrally distributed component.
SCTID
SCTID for a component in an extension.
SCTID Partition Values
00
A concept
01
A description
02
A relationship
03
A subset
04
A Cross Map set
05
A Cross Map target
10
A concept in an extension
11
A description in an extension
12
A relationship in an extension
13
A subset in an extension
14
A Cross Map set in an extension
15
A Cross Map target in an extension