Gello Expression Language

The GELLO Expression Language was started in 2001 and introduced in 2002; in 2005, GELLO was adopted as an international standard by Health Level Seven International and ANSI for a decision support language. GELLO Release 2 was completed and approved by ANSI in June 2010.[http://www.hl7.org/implement/standards/ansiapproved.cfm ANSI Approved Standards | HL7 International]

The GELLO specifications have been developed in coordination with the HL7 Clinical Decision Support TC (CDSTC).{{cite web| url = http://www.hl7.org/implement/standards/v3gello.cfm| url-status = dead| archive-url = https://web.archive.org/web/20100402170042/http://www.hl7.org/implement/standards/v3gello.cfm| archive-date = 2010-04-02| title = V3 Rules/GELLO}} As of 2021, the GELLO Implementation Guide DSTU was withdrawn from HL7 Version 3 due to inactivity. {{cite web| url=https://confluence.hl7.org/display/CDS/Withdraw+-+HL7+Version+V3+GELLO+IG%3A+CDS+Model+Definition+Language| title=Withdraw - HL7 Version V3 GELLO IG: CDS Model Definition Language| accessdate=2024-05-16}} However, Release 2 of the standard remains as is, despite a low level of use.

GELLO is a class-based object-oriented programming language and a relative of the Object Constraint Language (OCL). OCL is a well-developed constraint language that makes it attractive for use as an expression language. The intention was for GELLO to evolve as a standard query and expression language for decision support.{{cite journal|pmid=15360796 | volume=107 | issue=Pt 1 | title=Description and status update on GELLO: a proposed standardized object-oriented expression language for clinical decision support | year=2004 | journal=Stud Health Technol Inform | pages=164–8 | last1 = Sordo | first1 = M | last2 = Boxwala | first2 = AA | last3 = Ogunyemi | first3 = O | last4 = Greenes | first4 = RA}}

GELLO creates the potential for many decision support options, as the full array of atomic patient data is greatly accessible to complement better, safer clinical decision-making by health professionals. Furthermore, this enables specialist clinicians to customize their current systems and create flexible purpose built decision support systems.{{Cite web |url=http://ehealthaustralia.org/gello-a-decision-support-language/ |title=GELLO a Decision Support Language |access-date=2010-11-11 |archive-date=2011-08-15 |archive-url=https://web.archive.org/web/20110815130113/http://ehealthaustralia.org/article/gello-a-decision-support-language/ |url-status=dead }}

Standardization of GELLO has made this language compatible with the HL7 version 3.0 Reference Information Model (RIM). GELLO uses an abstract "virtual medical record" (vMR) so that the same GELLO code can run on multiple systems accessing data stored in different formats. The vMR is a simplified view of the HL7 RIM.[http://wiki.medical-objects.com.au/index.php/VMR_-_Virtual_Medical_Record VMR - Virtual Medical Record - Knowledgebase - Medical-Objects Knowledgebase]

The 2019 focus of the HL7 CDS WG was{{cite web |title=HL7 CDS Standards |url=http://wiki.hl7.org/index.php?title=HL7_CDS_Standards |accessdate=25 June 2019}} to build the Clinical Quality Language (CQL),{{cite web |title="Clinical Quality Language" | url=https://confluence.hl7.org/display/CDS/Clinical+Quality+Language |accessdate=2024-05-16}} version 1.5 of which was later published in 2020.{{cite web |title="HL7 Standard: Clinical Quality Language Specification, Release 1 Mixed Normative/Trial-Use (CQL 1.5)" | url=https://cql.hl7.org/ | accessdate=2024-05-16}}