GELLO Update

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(No Transcript)
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GELLO Update

• HL7 Working Group Meeting _at_ Baltimore
• 2nd October 2002
• Aziz Boxwala and Robert Greenes
• Brigham and Womens Hospital
• Harvard Medical School

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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

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Model
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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

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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

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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

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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

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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
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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
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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 gt creatinine_threshold) and
(product gt product_threshold) then
conclude true else conclude false
endif
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MLM in GELLO (data slot)
data creatinine Observation.allInstances-gt
select(coded_concept "C0428279") .sort(critical_
time.high).last() calcium
Observation.allInstances -gtselect(coded_concept
"C0428302") .sort(critical_time.high). last()
phosphate Observation.allInstances
-gtselect(coded_concept "C0428304") .sort(critic
al_time.high).last()
ListltObservationgt 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",'co
nstraints'"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()
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MLM in GELLO (data slot)
renal_failure_threshold PhysicalQuantity.new(2.
0, "mg/dl") renal_failure if
creatinine-gtnotEmpty and creatine.observed_quan
tity gt renal_failure_threshold then
true else false endif threshold_for_osteodystroph
y 70 calcium_phosphate_product if
calcium-gtnotEmpty and phosphate-gtnotEmpty
then calcium.observed_quantity.value
phospate.observed_quantity.value else -1 endif
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MLM in GELLO
logic renal_failure and calcium_phosphate_product
gt 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 gt
creatinine_threshold) and (product gt
product_threshold) then conclude true
else conclude false endif
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Implementation model
Application (e.g., Arden alert engine)
GELLO Interpreter
evaluate(ab)
result 7
Variable evaluator
valueOf(a)
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Observation.allInstances-gtselect()
Data retrieval
resultCollection/tuple
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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