Tuesday, October 28, 2008

Information and Communication Technologies Standards in the Health Sector

A new study has been released on behalf of the Enterprise & Industry Directorate General of the European Commission on the topic of ICT standards in the health sector: current situation and prospects.

The study contains a number of interesting remarks on HL7, for example welcoming the current initiative towards greater collaboration between HL7, ISO and CEN.

But there are also critical remarks, for example to the effect that:

Small or medium-sized ICT manufacturers may not be willing to adopt commonly used standards because these are very complex and thus difficult and expensive to implement. This applies for example to HL7 version 3. It may be less costly to develop proprietary standards on their own. (p. 21)

And also this:

HL7’s v2.x standards were important steps towards standardising clinical messaging. However, several issues caused difficulties, above all different options to implement the standard. To correct this issue, the RIM was developed for v3.0, eliminating most of the implementation options. The concept behind HL7 v3.0 has been generally well received. However, the RIM caused new problems. Firstly, it is unlikely that the defined RIM classes and attributes could be applied to every domain in healthcare – which is what they are intended to do. Secondly, the RIM documentation is described as being “disastrously unclear”, poorly integrated with HL7 v3.0 documentation, and inconsistent.

Under these circumstances, it may be difficult for HL7 v3.0 to establish a large user base. ... HL7’s involvement in the joint initiative with ISO and CEN may have the objective to move faster to international adoption of HL7 standards. The outcome of this convergence work as well as the organisation’s ability to create a satisfactory RIM may determine the future importance of HL7. (p. 37f.; emphasis added)

Thursday, October 09, 2008

Does the emperor have clothes?

This set of slides from a recent presentation by Eric Browne at an Australian national e-health conference provides some reassurance that the arguments I have been making on this blog are perhaps not simply the product of my own ignorance. Summary: "Basing clinical information interoperability on the HL7 v3 RIM is severely flawed. It is too complex; the underlying principles are unproved and highly suspect. The complexity leads to bad models, glacial progress, compromised quality and safety."

Postscript: Feb. 15, 2009
A more recent post by Eric Browne documenting problems with HL7 Clinical Document Architecture (CDA) is here.

Barriers, approaches and research priorities for integrating biomedical ontologies

Alan Rector has published an impressive survey of what we can expect for terminologies and ontologies in healthcare in the next ten years. Summarizing a long document, Rector believes:
  • HL7 (a mix of versions) will dominate the standards for messaging.
  • The standard for EHRs is likely to be a combination or amalgam of the HL7 CDA and Archetype based standards from OpenEHR, CEN EN 13606.
  • Terminologies from biomedicine, particularly the Gene Ontology and the associated ontologies in the Open Biomedical ontologies consortium will become of increasing importance to clinical medicine.
  • Following the example of the bioinformatics community, open systems “owned” by their community are likely to make an increasing contribution.

Rector echoes a number of what one might be tempted to call 'philosophical' points addressed in this blog as concerns the relations between ontologies and information models. He nicely summarizes these points as follows:

The relationship between knowledge representation and ontologies remains controversial and plagued by confusion of substance compounded by loose use of language. A second closely related notion is that of an “information model” of “model of data structures”. Both Archetypes and HL7 V3 Messages are examples of data structures. Formalisms for data structures bear many resemblances to formalisms for ontologies. ... However, there is a clear difference.

  • Ontologies are about the things being represented – patients, their diseases. They are about what is always true, whether or not it is known to the clinician.For example, all patients have a body temperature (possibly ambient if they are dead); however, the body temperature may not be known or recorded. It makes no sense to talk about a patient with a “missing” body temperature.
  • Data structures are about the artefacts in which information is recorded. Not every data structure about a patient need include a field for body temperature, and even if it does, that field may be missing for any given patient. It makes perfect sense to speak about a patient record with missing data for body temperature.

A key point is that “epistemological issues” – issues of what a given physician or the healthcare system knows – should be represented in the data structures rather than the ontology. This causes serious problems for terminologies coding systems, which often include notions such as “unspecified” or even “missing”. This practice is now widely deprecated but remains common.

Under 'desirable outcomes', he lists:

The methods will become increasingly formal. The conflict between the scaling problems presented by pre-coordinated terminologies and the difficulty of maintaining consistency with post-coordinated terminologies will be overcome. To this end, the formal structure of SNOMED-CT and will be radically revised to take advantage of its purported underpinnings in description logic. HL7 v3 and/or Archetypes will likewise be reformulated to take advantage of modern technologies to ensure their mutual consistency and consistent binding to the new terminologies. Common links to terminologies from OBO and others used in molecular biology will be forged.

And under 'outcomes to be avoided':

enormous resources will be spent on over-ambitious plans for semantic interoperability that inevitably fail. In either case, communication will take place by going around rather than via the clinical information systems. In countries where it is mandated, SNOMED and HL7 V3 will become taxes on healthcare, absorbing significant resources while returning no, or in some cases negative, benefits.

The document as a whole contains a wealth of important material on HL7 V3 -- and SNOMED CT -- and on the problems associated with each. It draws special attention to HL7 15 year-long planning process designed to produce a '“version 3” that is not yet in routine use'.

Flavors of Null

Interesting post from Ananda Mohan concerning the problems created by HL7 v3's lack of support for any kind of optionality. One result of this policy is that codes need to be provided in advance to cover all cases where information is missing -- hence the multiple 'flavors of null', which, are listed by Mohan on the basis of the latest HL7 v3 ballot pack as follows:
1. NI: "no information" - this is the most general and default exceptional value. There is no information which can be inferred from this exceptional value.

2. MSK: "masked" - this particular item has a known proper value, but it cannot be released in a given context due to security, privacy or other reasons.

3. OTH: "other" - there is a value, but it is not an element in the value domain of a variable, with particular cases:
- NINF: "negative infinity of numbers"
- PINF: "positive infinity of numbers"

4. UNK: "unknown" - a proper value is applicable, but not known. In particular:
- ASKU: "asked but unknown" – information was sought from the source but not known (e.g., patient was asked but didn't know)

- NAV: "temporarily not available" - information is not available at this time but it is expected that it will be available later.

- NASK: "not asked" - the Information was not requested from the patient

- QS: "sufficient quantity" – The actual quantity is not known but sufficient enough to achieve a specific goal. For example the advice can be: add a sufficient quantity of water to 10 mg of medicine.
- TRC: "trace" – The content is too small to measure but still a non-zero value.

5. NA: "not applicable" – There is no proper value for this data item for this patient; for example, the date of the last menstrual period is not applicable for a male.
All of these “flavors” are provided for every data type. Thus for example “null” is a possible value of an integer or real alongside actual integer and real values As Mohan points out, this might lead to reasoning problems: the HL7 definition of 'Boolean', in contrast to every working formalism, implies a 3-valued logic. The null flavors are causing problems also for the (surely in any case premature) attempts by ISO to model its health data types standard (ISO 20190) on HL7 v3 data types. Organizations such as CEN have, it seems, opposed the current ISO draft, in part because of the problems generated by the usage of null flavors.
These problems were described in detail already five years ago in a document on the openEHR Data Types Information Model, the latest version of which is here:
All HL7 data types inherit from the ANY class (equivalent to the DATA_VALUE class in openEHR) which contains the attributes:
BL nonNull;
CS nullFlavor;
BL isNull;
The purpose of these attributes is to indicate whether a datum is Null, and for what reason. Since some data type classes also appear as the attributes of other data types, the Null markers also ndicate whether any part of a datum is null. ... this allows an interval with missing ends and width to exist as a structured type. The consequence of the approach is that the entire model is essentially a model of "partial" data types; any attribute and any function call may return a Null value, as well as the true values of its type (in fact, in the specification, Null values are defined to be valid values of all data types).
This design decision was taken in HL7 so that any datum, no matter how unknown, would be structurally representable in the same way as completely known data, enabling it to be processed in the same way as all other instances of the same type. However, an important object-oriented design principle has been ignored in this approach. In the proper design of classes, properties and class invariants are stated. Invariants are statements which describe the correctness conditions of instances of the class; the general rule is that the post-condition of a creation routine (constructor) of a class must be that the invariants are satisfied. For example, an invariant of the HL7 IVL class could be:
(exists(low) and exists(high)) or else
(exists(low) and
exists(width)) or else
(exists(width) and exists(high))
When an instance of this class is created, this condition should be satisfied, and remain satisfied for the life of the instance. To do otherwise is to create instances ofdata which other software can make no assumptions about, and is forced to check every single field, and then determine what to do in an ad hoc way. ... Possible consequences of the built-in Null marker design approach include:
• since even HL7’s basic types ST, INT, REAL, LIST<>, SET<> include null markers, processing of null values will be pervasive at the lowest level;

• software will be more complex, both implementations of the data types, and of software which handle them. This is because the software always has to deal with the possibility of calls to routines and attributes returning Null values. Most clinical information systems to date have taken the approach that a datum is either represented as an instance of a formal type if fully known, or else as narrative text if only partial;

• data may not be always be safely processable, since some software may not properly handle the null values associated with attributes of partially known data items.
Essentially, all software which processes the data has to be “null-value aware”, and make no assumptions at all about whether a particular data instance is valid or not.
For all of these reasons the HL7 data type model is in stark contrast with the much simpler approaches used in CEN and in openEHR.

Postscript May 23, 2011

See also now here: http://wolandscat.net/2011/05/18/the-hl7-null-flavor-debate-part-2/