Current Version - Under Revision
Selective retrieval is an essential function for a health record system. There are two main types of requirements:
Example: Active problems/diagnoses, current medication, recent investigation results or blood pressure readings.
Example: To check the record for specified symptoms, findings, investigations, procedures or diagnoses.
The following subsections address issues and requirements that are common to all types of retrieval.
The following sections identify factors that may influence performance when undertaking selective data retrieval. There are no fixed rules for optimization of retrieval performance. Application developers should interpret the issues outlined in the guide in the light of their experience with the operating systems and data management tools that they use.
An evaluation of different approaches to retrieval was undertaken for the NHS, in connection with work on Clinical Terms Version 3 implementation. This showed that the "best" approach was not the same for all relational databases. Some software environments favor one approach while a different approach may be more effective in another environment. Therefore, it is likely that some of the factors discussed will have a significant impact on some developers, while being less relevant in others.
The quality of selective retrieval is measured in terms of two factors:
The semantic structures of SNOMED CT assist application developers to achieve these goals by allowing different expressions that represent the same or similar information to be recognized and compared (see 11 Supporting Selective Data Retrieval ).
The meaning of a SNOMED CT expression may be modified by the context in which it is used. Aspects of this context are represented by:
Storing similar information in differing structures complicates retrieval since each query must take account of alternative ways in which the required information may be stored. As a result the semantic strength of SNOMED CT may be obscured by the varied approach to structure. Therefore, realization of the full potential benefit of SNOMED CT, requires an information model that accommodates SNOMED CT expressions and ensure consistent storage of similar information.
Another limiting factor for retrieval is the consistency and completeness of recording. The extent of use of SNOMED CT depends in part of policy and guidance at national or organizational levels, which in turn depends on requirements and priorities for data retrieval and reuse. From a technical implementation perspective a key factor in delivering consistent retrieval is a user-interface that facilitates, simplifies and encourages consistent data entry which uses SNOMED CT expressions to the extent need to meet relevant requirements.
Before addressing the specifics of SNOMED CT related retrieval criteria it is important to recognize that these only form one part of the picture. Most selective retrieval criteria will include a mixture of predicates, some of which apply to SNOMED CT encoded data and some of which apply to other data in the patient record. This non - SNOMED CT encoded data includes:
The interplay of these factors with SNOMED CT encoded data may affect the optimum approach for data retrieval. Some non - SNOMED CT encoded retrieval criteria may significantly reduce the potential set of patients or in patient record entries that qualify for retrieval. In these cases, it may be useful to apply these criteria before testing SNOMED CT specific criteria.
These examples illustrate a general point rather than to offer guidance on the specific searches. It is important to bear in mind that the performance, completeness and specificity of retrieval are dependent on the structure of the record as well as the semantics of SNOMED CT .