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GELLO Update

GELLO Update. HL7 Working Group Meeting @ Baltimore 2 nd October 2002 Aziz Boxwala and Robert Greenes Brigham and Women’s Hospital Harvard Medical School. What is GELLO?. Expression language Query language maps variables in expressions to data in external systems Embedded language

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GELLO Update

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  1. HL7 @ Baltimore

  2. GELLO Update HL7 Working Group Meeting @ Baltimore 2nd October 2002 Aziz Boxwala and Robert Greenes Brigham and Women’s Hospital Harvard Medical School

  3. What is GELLO? • Expression language • Query language • maps variables in expressions to data in external systems • Embedded language • Can be used as part of other specs • MLM, guidelines, RIM, template constraints, etc. • Goal is to facilitate sharing of knowledge HL7 @ Baltimore

  4. Arden Syntax Guideline (Sequential Knowledge) RIM Expressions (Ontology) Other DS & KBs GELLO Q&E GELLO Q&E GELLO Q&E GELLO Q&E vMR Object-oriented data model Model HL7 @ Baltimore

  5. Status report • As of May 2002 meeting, we had agreed to bring this to TC ballot • But decided to defer because of desire to: • Reduce complexity of syntax • Make more compatible with generic language specification efforts • Eliminate side effects in expressions • Facilitate use as embedded language distinct from other elements of an application, e.g., those that do assignment or flow control • Revised language specification developed • To be presented here HL7 @ Baltimore

  6. Requirements - 1 • Work with an object-oriented data structure compatible with the RIM • Should support different data models (such as VMR) • Be platform independent • Be easy to write and read for defined class of users • Be usable in different ‘applications’ (Arden MLMs, guidelines, templates, …) • Leverage existing standard frameworks/languages where possible HL7 @ Baltimore

  7. Requirements - 2 • Be side-effects free • Built-in data types (if any) should be compatible with those defined in the RIM • Be extensible • classes must be compatible with the RIM and language framework • Be free of ambiguities HL7 @ Baltimore

  8. Using OCL grammar • Object Constraint Language • Part of UML spec • Object Management Group standard • Language for specifying invariants on classes and its member attributes and functions • Not a complete programming language • Side-effects free • Maps to our needs and requirements HL7 @ Baltimore

  9. An example with an MLM maintenance: title: Screening for elevated calcium-phosphate product;; library: purpose: provide an alert if the product of the blood calcium and phosphorus exceeds a certain threshold in the setting of renal failure;; explanation: An elevated Ca-PO4 product suggests a tendency toward renal osteodystrophy and predisposes to soft-tissue calcification;; HL7 @ Baltimore

  10. …MLM knowledge: data: /* trigger on Ca, PO4 or Cr */ creatinine := read last {'dam'="PDQRES2",'constraints'="C****"; ;'32752'}; calcium := read last {'dam'="PDQRES2",'constraints'="C****"; ;'32109'}; phosphate := read last {'dam'="PDQRES2",'constraints'="C****"; ;'33824'}; creatinine_threshold := 2; product_threshold := 70; HL7 @ Baltimore

  11. …MLM logic: if (creatinine is not number) or (calcium is not number) or (phosphate is not number) then conclude false; endif; product := calcium * phosphate; if (creatinine >= creatinine_threshold) and (product >= product_threshold) then conclude true; else conclude false; endif; HL7 @ Baltimore

  12. MLM in GELLO (data slot) data: creatinine := Observation.allInstances->select(coded_concept= "C0428279") .sort(critical_time.high).last() calcium := Observation.allInstances ->select(coded_concept= "C0428302") .sort(critical_time.high).last() phosphate := Observation.allInstances ->select(coded_concept = "C0428304") .sort(critical_time.high).last() List<Observation> := last(select obs from Observation as obs where obs.service_cd.equals(new Concept(“MTH”, “C042879”)) sort descending obs.critical_time.high); creatinine := read last {'dam'="PDQRES2",'constraints'="C****"; ;'32752'}; There are ways to make the GELLO query syntax easier – for example by defining class/static functions in VMR classes to retrieve instances Observation.select(coded_concept = "C0428279").last() HL7 @ Baltimore

  13. … MLM in GELLO (data slot) • renal_failure_threshold := PhysicalQuantity.new(2.0, "mg/dl") • renal_failure := • if creatinine->notEmpty and • creatine.observed_quantity > renal_failure_threshold then • true • else • false • endif • threshold_for_osteodystrophy := 70 • calcium_phosphate_product := • if calcium->notEmpty and phosphate->notEmpty then • calcium.observed_quantity.value * phospate.observed_quantity.value • else • -1 • endif HL7 @ Baltimore

  14. … MLM in GELLO logic: renal_failure and calcium_phosphate_product > threshold_for_osteodystrophy if (creatinine is not number) or (calcium is not number) or (phosphate is not number) then conclude false; endif; product := calcium * phosphate; if (creatinine >= creatinine_threshold) and (product >= product_threshold) then conclude true; else conclude false; endif; HL7 @ Baltimore

  15. Implementation model Application (e.g., Arden alert engine) GELLO Interpreter evaluate(a+b) result: 7 Variable evaluator valueOf(a) 5 Observation.allInstances->select(…) Data retrieval result:Collection/tuple HL7 @ Baltimore

  16. Issues • Side-effect free language • Constructors • Restructuring of MLM… Let expressions • Built-in datatypes • Same specification or different? • Reconciling OCL standard lib with HL7 datatypes • Writing back data • Observation.write(…) • Exception management HL7 @ Baltimore

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