=Paper=
{{Paper
|id=Vol-1428/BDM2I_2015_paper_8
|storemode=property
|title=Multi-Strategy Semantic Web Reasoning for Medical Knowledge Bases
|pdfUrl=https://ceur-ws.org/Vol-1428/BDM2I_2015_paper_8.pdf
|volume=Vol-1428
|dblpUrl=https://dblp.org/rec/conf/semweb/WoenselMAA15
}}
==Multi-Strategy Semantic Web Reasoning for Medical Knowledge Bases==
https://ceur-ws.org/Vol-1428/BDM2I_2015_paper_8.pdf
Multi-Strategy Semantic Web Reasoning for Medical
Knowledge Bases
William Van Woensel, Hossein Mohammadhassanzadeh, Samina Abidi, Raza Abidi
NICHE Research Group, Faculty of Computer Science,
Dalhousie University, Halifax, Canada
{william.van.woensel, hassanzadeh, samina.abidi, raza.abidi}@dal.ca
Abstract. Semantic Web technology offers excellent advantages for real-world
medical knowledge bases, both on and off the Web. Based on ontologies from
(bio)medical domains, OWL inferencing enhances knowledge bases with new
facts, while deductive rules, written in semantic rule languages, supply additional
inferences based on deterministic knowledge from e.g., Clinical Practice
Guidelines (CPG). We argue that other mechanisms, representing weaker forms
of inferencing, are also useful in dealing with incomplete healthcare knowledge.
This includes inductive generalization, which leverages data similarities to
induce new rules, and analogical reasoning, which relies on plausible domain
knowledge. To cope with their shortcomings, we propose integrating such weak
inferencing with a single, explanation-based generalization, allowing us to
leverage their complementary strengths as well as apply a tutor-based paradigm
for verification. In this integrated approach, justifications are generated
explaining the potential correctness of queries, where missing medical
knowledge is compensated by injecting plausible inferences. Based on their
expertise, healthcare experts may then confirm particular justifications,
materializing them in the knowledge base. Inversely, we argue that by leveraging
OWL ontological knowledge, weak inferencing methods benefit from Semantic
Web technology as well.
Keywords: medical knowledge bases, Semantic Web reasoning, explanation-
based generalization, inductive generalization, analogical reasoning
1 Introduction
Clinical Decision Support Systems (CDSS) are knowledge-based systems, designed to
assist health professionals in making ‘evidence-informed’ clinical decisions, based on
the best evidence and approved clinical protocols [1] in concert with a patient’s medical
records [2]. Given a clinical case, a CDSS reasons over the available knowledge to
generate evidence-based recommendations for diagnosis/therapy, alerts, risk
assessments and order sets. For the knowledge base of a CDSS, the source of
knowledge are published, evidence-based clinical guidelines and the expert’s clinical
experiences [3]. Developing a complete and consistent clinical knowledge base
therefore is a major undertaking, as it requires (a) the computerization of the clinical
guidelines in terms of decision rules, (b) the validation of the abstracted rules to ensure
relevance, consistency and conciseness, and (c) implementing the validated rules in
terms of an executable knowledge representation formalism. To realize medical
knowledge bases, the Semantic Web framework offers a formal, logic-based framework
for modeling the knowledge from clinical guidelines—i.e., via expressive biomedical
OWL ontologies, allowing clinical facts to be inferred based on utilized ontological
constructs; and using deductive rule languages, such as RuleML, SPIN or SWRL,
which allow applying deterministic knowledge to infer clinical conclusions. From a
knowledge engineering perspective, we posit that semantic ontologies are particularly
useful for representing and reasoning over medical knowledge bases. This observation
is reflected by work in CDSS likewise applying Semantic Web technology [4–6].
Additionally, we argue that useful mechanisms for enriching semantic medical
knowledge bases are not limited to a priori, deterministic knowledge. To further extend
the knowledge closure, other mechanisms can be considered as well, for instance based
on data similarities and plausible knowledge (i.e., knowledge that will likely not hold
in all possible situations). Inductive generalization hypothesizes that commonalities
between data entities likely account for a particular shared feature; this knowledge can
then be formalized in terms of rules [7]. Analogical reasoning is guided by plausible
domain knowledge, implying if two data entities are similar in one specific aspect, they
are likely similar in another as well [8]. These two approaches are complementary:
induction is a data-intensive approach, requiring a large number of positive examples;
while analogy relies on less data, but requires the presence of (plausible) knowledge.
In any case, these kinds of reasoning (also including e.g., abductive reasoning [9]) are
considered weaker forms of inferencing, as they do not guarantee the truth of inferred
knowledge [7]. This is especially problematic in medical settings, where drawing
correct, evidence-based conclusions from the available data is paramount. An effective
way to cope with this tentative nature is by integrating multiple weak methods with
deterministic, explanation-based generalization, allowing their complementary
strengths to be leveraged [7, 10, 11]. Based on facts and deductive rules, this
generalization constructs justifications that explain why a given statement may be
correct [11]. In an integrated approach, weak inferencing is applied when full
deterministic knowledge is lacking, yielding plausible justifications that are
supplemented with weak inferences [10]. Importantly, such integrated justifications
allow medical domain experts to carefully weigh the tentative data and mechanisms
used in the process. The expert may then choose to confirm and fine-tune a particular
justification, to be materialized in the knowledge base for future re-use.
We argue that a multi-strategy reasoning approach is useful for enhancing access to
medical semantic knowledge bases. In particular, we present a Semantic Web medical
expert system that generates & presents plausible justifications to medical experts,
using deterministic and plausible inferencing methods. This expert can further confirm
and fine-tune particular justifications to add them to the knowledge base. In contrast to
fully automated mechanisms, our approach combines machine inferencing capabilities
with the tacit, medical experience of human experts, resulting in fully human-verified
knowledge bases. Inversely, we argue that the accuracy of weak inferencing methods
can be improved by leveraging Semantic Web technology, thus enhancing their utility
in the knowledge engineering cycle. In particular, rich ontological knowledge can be
leveraged to improve data similarity checking, as well as increase the expressivity of
plausible knowledge. Our semantic expert system accepts RDF, OWL ontologies and
deductive semantic rules (SPIN rules) as input, and generates plausible justifications
for presentation, verification and fine-tuning by the domain expert. Confirmed
justifications are transformed into RDF triples and added to the knowledge base.
In Section 2, we elaborate on the reasoning layer of our expert system, discussing
explanation-based generalization, inductive generalization and analogical reasoning.
Section 3 details the UI providing query access to the domain expert. In Section 4, we
summarize our expert system implementation. Section 5 presents related work, and
Section 6 finally ends with conclusions and future work.
2 Reasoning Layer
A logical first step to supplementing incomplete Semantic Web knowledge bases is
to apply ontology inferencing; i.e., leveraging domain-specific, ontological knowledge
to infer new information. As a second step, our integrated approach taps an additional
source of deterministic knowledge, namely deductive Semantic Web rules. At its core,
our approach applies explanation-based generalization, which constructs justifications
explaining why a given query instance is correct. This generalization is implemented
via backward chaining, which recursively finds rules proving the query statement. In
this process, premises of found rules may be proven by knowledge base facts or again
by other deductive rules; either ending when all involved premises have been proven,
or when some premises were found to be unsatisfiable.
This is illustrated in Figure 2, which visualizes the initial query justification as a tree
structure. We note that for clarity, figures and rules use predicate logic notation
(namespaces are omitted), and type restrictions on arguments are abbreviated as nested
“(type X)” statements. In the tree, the root represents the query instance; leafs stand for
facts in the knowledge base (solid line) or missing premises (dashed line); and
intermediate nodes represent conjunctive rule premises, connected via directed edges
to the rule conclusion. Grey-shaded leafs are facts inferred via ontology reasoning.
Fig. 1. Initial justification tree.
To explain our multi-strategy reasoning approach, we present a medical use case,
where the system is asked to explain whether patient p01 should be recommended
Azithromycin, an antibiotic typically used to treat bacterial infections. Below, we show
the deductive rules used to build the initial justification tree:
recommend(P, Azithromycin) : − type(P, Adult), type(P, NoLiverDiseasePatient),
illness(P, ChronicBronchitis), illness(P, (type Pneumonia)) .
illness(P, ChronicBronchitis) : − symptom(P, (type Cough)), symptom(P, Fatigue),
symptom(P, (type Chills)), symptom(P, SlightFever) .
Fig. 2. Deductive rules used in explanation-based generalization.
We note that the lack of liver disease history was inferred via an OWL property
cardinality restriction:
cds:NoLiverDiseasePatient rdfs:subClassOf [
a owl:Restriction ;
owl:maxQualifiedCardinality “0” ;
owl:onProperty cds:illness ;
owl:onClass cds:LiverDisease ] .
Fig. 3. OWL constraint cds:NoLiverDiseasePatient.
In the knowledge base, each current and past patient illness is recorded using the
illness property. In case patients are not linked via the illness property to any instance
of LiverDisease, this constraint implies that they are member of the
cds:noLiverDiseasePatient class extension.
Currently, the cough symptom and pneumonia diagnosis are missing for p01, leading
to an incomplete justification. To prove the correctness of the missing premises,
inductive generalization and analogy-based reasoning are applied, resulting in a
plausible justification tree that incorporates multi-strategy inferencing results. We
elaborate on these two methods in the subsections below.
2.1 Analogy-based reasoning
Analogical inferencing supplements an incomplete knowledge base by implying that
two entities who are similar in a particular aspect, are likely similar in another specific
aspect as well. As such, knowledge can be transferred from a well-known entity S to a
similar, lesser known entity T [8, 12, 13]. This kind of reasoning is guided by plausible
rules of the form [7]:
𝑄(𝑋, 𝑌): ~𝑃(𝑋, 𝑍)
Fig. 4. General structure of a plausible rule.
This rule states that “Q is plausibly determined by P”, meaning if two entities S and
T are both characterized by the same feature P, then they will likely also share feature
Q. Below, we show a relevant plausible rule from our medical use case:
illness(P, (type Pneumonia)) :~ type(P, ReducedImmunityPatient), symptom(P, (type
ShortnessOfBreath)), symptom(P, (type Fever)), symptom(P, ShakingChills)
Fig. 5. Example plausible rule.
This rule indicates that two data entities sharing particular characteristics and
symptoms, namely a reduced immune system, a type of shortness of breath, a type of
fever and shaking chills, will likely share the same kind of pneumonia. This example
shows how ontological knowledge may be leveraged to increase the expressivity of
plausible rules. In particular, by allowing to specify rules at arbitrary levels of
granularity: any kind of fever, shortness of breath or reduced immune system suffices
as knowledge-transfer condition, while the patient should exhibit “shaking chills” in
particular. We note that the rule only specifies which kinds of features will collectively
account for a type of pneumonia; the particulars are left up to the well-known entity.
Below, we show RDF statements for patient p07 and p01:
cds:p07 rdf:type cds:OrganTransplantPatient ; cds:symptom cds:ShortBreathOnExertion
cds:symptom cds:MediumFever ; cds:symptom cds:ShakingChills ;
cds:illness cds:ViralPneumonia ; …
cds:p01 rdf:type cds:HIVP\atient ; cds:symptom cds:ShortBreathOnExertion
cds:symptom cds:MediumFever ; cds:symptom cds:ShakingChills ; …
Fig. 6. RDF code describing entities p01 and p07.
By sharing the same kind of shortness of breath (i.e., ShortBreathOnExertion), fever
(i.e., MediumFever) and “shaking chills”, p01 shares almost all the required
characteristics with p07. By further leveraging ontological knowledge, the system can
cope with inexact matches as well; in particular, the system is able to infer that
HIVPatient and OrganTransplantPatient are both subtypes of
ReducedImmunityPatient. Based on the ontology hierarchy, our system can calculate
and present accurate concept similarities to the medical expert. In Section 2.2, we
elaborate on establishing such semantic similarities. Regarding our example, since
patient p01 adheres to the knowledge-transfer condition (in italic), it can be plausibly
inferred that p01 has viral pneumonia (in bold).
Table 1 shows the pseudocode for analogical reasoning in our expert system. The
analogical reasoning process is driven by failed justification premises. In this case, the
process starts by looking for plausible rules that may resolve a missing premise (line
1). The knowledge base is then searched for facts that unify the rule; i.e., match the rule
condition and consequent (line 2). For each found fact, the algorithm checks whether
its instantiated knowledge-transfer condition matches the original entity (line 3). If so,
its consequent is added to the entity, at least in the system’s working memory (line 4).
If the expert confirms the overall justification, the working memory will be materialized
in the knowledge base.
1. given failed premise, query KB for plausible rules that infer the missing property
𝒆𝒙𝒂𝒎𝒑𝒍𝒆 𝒒𝒖𝒆𝒓𝒚: 𝑖𝑙𝑙𝑛𝑒𝑠𝑠(𝑝01, (𝑡𝑦𝑝𝑒 𝑃𝑛𝑒𝑢𝑚𝑜𝑛𝑖𝑎))
→ 𝑓𝑖𝑛𝑑_𝑝𝑙𝑎𝑢𝑠𝑖𝑏𝑙𝑒_𝑟𝑢𝑙𝑒𝑠(𝑖𝑙𝑙𝑛𝑒𝑠𝑠(𝑋, (𝑡𝑦𝑝𝑒 𝑃𝑛𝑒𝑢𝑚𝑜𝑛𝑖𝑎)), 𝐾𝐵) = { 𝑟𝑢𝑙𝑒𝑖 }
2. for each plausible rule, find KB facts that unify the rule
𝑢𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛𝑠 = { ∀ 𝑟𝑢𝑙𝑒𝑖 : 𝑢𝑛𝑖𝑓𝑖 = 𝑢𝑛𝑖𝑓𝑦(𝑟𝑢𝑙𝑒𝑖 , 𝐾𝐵) }
3. for each unification, check whether its condition matches the input entity
𝑟𝑒𝑠𝑢𝑙𝑡𝑠 = { ∀ 𝑢𝑛𝑖𝑓𝑖 : 𝑟𝑒𝑠𝑢𝑙𝑡𝑖 = 𝑚𝑎𝑡𝑐ℎ𝑒𝑠(𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛(𝑢𝑛𝑖𝑓𝑖 ), 𝑝01) }
4. add the consequent of a positive match to the input entity
𝑝01 ← 𝑐𝑜𝑛𝑠𝑒𝑞𝑢𝑒𝑛𝑡(𝑢𝑛𝑖𝑓𝑖 )
Table 1. Analogical reasoning algorithm
Figure 8 illustrates part of our justification tree extended by analogical reasoning.
Fig. 7. Part of justification tree extended by analogical reasoning.
2.2 Inductive generalization
Inductive generalization generates new deterministic knowledge, based on
similarities between facts in the knowledge base. Given a particular feature, the
knowledge base is searched for a set of entities sharing the feature (called “positive
coverage”). Other similarities between these entities are hereby hypothesized as
accounting for the feature [7]. Applying inductive reasoning gives rise to the following
type of rule:
𝑓𝑒𝑎𝑡𝑢𝑟𝑒(𝑋, 𝑣𝑎𝑙𝑢𝑒): −𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦𝑆𝑖 (𝑋)
Fig. 8. General structure of an induced rule
Where feature(X, value) represents the input feature, and similaritySi represents
similarities between the found entities Si. By applying this rule, the feature value is thus
inferred for any entity X, which exhibits the characteristics assumed to account for the
feature. We note that in this process, the number of matching entities (positive
coverage) strengthens the validity of the hypothesis. Below, we discuss different ways
of determining entity similarity.
A good basis for finding commonalities is to take the conjunction between entity
properties, i.e., all shared properties [7]. As mentioned before (see Section 3.1),
conceptual similarity between entity types can be considered as well. Calculating
semantic concept similarity has been studied extensively in the literature (e.g., [14, 15]).
Typically, these works determine concept similarity by calculating their conceptual
distance, indicated by the distance to their closest common subsuming concept. It is
further argued that two “specific” concepts, lower in the concept hierarchy, will be
more similar than two “abstract” concepts [15]. We rely on the well-known measure
suggested by Wu and Palmer [14], which considers both conceptual distance and
concept specificity:
2 × 𝑁3
𝐶𝑜𝑛𝑆𝑖𝑚(𝐶1 , 𝐶2 ) =
𝑁1 + 𝑁2 + 2 × 𝑁3
Fig. 9. Conceptual similarity calculation
Where C3 is the closest common parent of C1 and C2; N1 is the number of nodes
on the path from C1 to C3, and N2 is the number of nodes between C2 and C3
(indicating conceptual similarity); and N3 is the number of nodes on the path from C3
to the root (indicating conceptual specificity). In our approach, the medical expert will
use this information to confirm, fine-tune or reject an inference (see Section 4).
The following RDF code shows two similar entities p11 and p15, which share a
number of characteristics as well as a particular feature currently missing from our
justification tree (see Figure 2):
cds:p11 cds:symptom cds:SlightFever ; cds:symptom cds:ChestDiscomfort
cds:symptom cds:MucusProduction ; cds:symptom cds:CoughWithMucus ; …
cds:p15 cds:symptom cds:SlightFever ; cds:symptom cds:ChestDiscomfort
cds:symptom cds:MucusProduction ; cds:symptom cds:CoughWithMucus ; …
Fig. 10. RDF code describing similar entities p11 and p15.
In this case, the following deductive rule could be inferred (positive coverage of 2):
symptom(P, CoughWithMucus) : − symptom(P, SlightFever),
symptom(P, ChestDiscomfort), symptom(P, MucusProduction)
Fig. 11. Rule generalized via inductive reasoning.
We note that, depending on the facts in the knowledge base, different sets of shared
characteristics may yield the same missing feature, meaning multiple deductive rules
could be inferred. Table 2 shows the pseudocode for inductive reasoning in our system.
As before (see Table 1), the process is triggered by a failed premise in the justification
tree. Firstly, the knowledge base is queried with (a generalized version of) the failed
premise, to retrieve all entities with the missing property value (line 1). Subsequently,
similarity is determined between matching entities and the query entity (line 2) using
the similarity function (see Figure 9). The next step is to aggregate equivalent
similarities (i.e., involving the same property values), thus collecting the necessary
information (e.g., positive coverage) for each potential deductive rule (line 3).
Afterwards, deductive rules are generated based on these aggregated similarities (line
4). These will be presented to the domain expert (see Section 4), who can possibly
choose one of the rules to be added to the knowledge base.
1. given failed premise, query KB for matching facts
𝒆𝒙𝒂𝒎𝒑𝒍𝒆 𝒒𝒖𝒆𝒓𝒚: 𝑠𝑦𝑚𝑝𝑡𝑜𝑚(𝑝01, (𝑡𝑦𝑝𝑒 𝐶𝑜𝑢𝑔ℎ))
→ 𝑓𝑖𝑛𝑑_𝑚𝑎𝑡𝑐ℎ𝑖𝑛𝑔_𝑓𝑎𝑐𝑡𝑠(𝑠𝑦𝑚𝑝𝑡𝑜𝑚(𝑋, (𝑡𝑦𝑝𝑒 𝐶𝑜𝑢𝑔ℎ)), 𝐾𝐵) = { 𝑟𝑒𝑠𝑢𝑙𝑡𝑖 }
2. using similarity function, determine similarity between results and initial entity
𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑖𝑒𝑠 = { ∀ 𝑟𝑒𝑠𝑢𝑙𝑡𝑖 : 𝑠𝑖𝑚𝑖 = 𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦(𝑟𝑒𝑠𝑢𝑙𝑡𝑖 , 𝑝01) }
3. aggregate equivalent similarities
𝑎𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒𝑑 = { ∀ 𝑠𝑖𝑚𝑖 , 𝑠𝑖𝑚𝑗 (𝑖 ≠ 𝑗): 𝑠𝑖𝑚𝑖 = 𝑠𝑖𝑚𝑗 → 𝑎𝑔𝑔𝑟_𝑠𝑖𝑚( 𝑠𝑖𝑚𝑖 , 𝑠𝑖𝑚𝑗 ) }
4. generate deductive rules based on aggregated similarities
𝑟𝑢𝑙𝑒𝑠 = { ∀ 𝑎𝑔𝑔𝑟_𝑠𝑖𝑚𝑖 : 𝑓𝑒𝑎𝑡𝑢𝑟𝑒(𝑋, 𝑣𝑎𝑙𝑢𝑒): −𝑎𝑔𝑔𝑟_𝑠𝑖𝑚𝑖 (𝑋) }
Table 2. Inductive generalization algorithm
In Figure 12, we show part of the justification tree extended by induction.
Fig. 12. Part of justification tree extended by inductive generalization.
3 User Interface Layer
In our Semantic Web expert system, healthcare experts query the knowledge base.
In Section 2, we elaborated on how multiple reasoning mechanisms cooperate in
creating plausible query justifications. In this section, we illustrate how our system
presents these justifications, and their plausible extensions, to the medical expert.
Fig. 13. User Interface: Main query interface
Figure 13 shows the main query interface, which presents the user with one or more
justifications to explain a posed query, visualized as trees (see Figure 2). As shown,
failed premises are highlighted in red. Upon selecting a failed premise, a list of
automatic resolution options are shown (see Figure 14, right-panel), as well as a short
description. After selecting the analogy resolution, the screen in Figure 15 is shown.
In this screen, the top part describes the plausible rule being applied, using color
coding to indicate shared variables/instances between the rule conjuncts. The bottom
shows the found unification of the rule (see Section 3.1), as well as the inference that
could be made by analogy. As mentioned, ontological knowledge may be leveraged to
cope with inexact matches. In this case, HIVPatient and OrganTransplantPatient do
not match exactly, but were found to have a direct common subsumer, namely
ReducedImmunityPatient. This semantic similarity is presented to the domain expert,
together with the calculated score (see Figure 10).
Fig. 14. User Interface: Analogical Reasoning screen
Fig. 15. User Interface: Inductive Generalization screen
Figure 16 shows the inductive generalization screen. At the top, the screen indicates
properties found by the system that can account for the missing premise (see Section
3.2). Below, the deductive rule is shown that may be induced, accompanied by the
missing premise that the deductive rule would infer. Before confirming the inference,
the domain expert can fine-tune the rule to cope with inductive bias. Firstly, the expert
can select any instance or type to select any of their (super or sub) types in the related
concept hierarchy, making the instance or type more general or specific. In this case,
the domain expert chooses to replace the SlightFever condition by (type Fever), as any
kind of fever may indicate a cough. After clicking SlightFever, a popup shows the Fever
concept hierarchy, which allows the expert to choose any related concept. In addition,
the expert may add (see “+” icon) or remove any premise from the rule condition. For
instance, the domain expert could decide that having chest discomfort is unrelated to
cough, and thus remove the premise from the condition.
After accepting an automatic resolution option, the visualized justification tree (see
Figure 14) is extended with the plausible inference nodes (highlighted in orange; not
shown). In addition, its inferences will be added to the system’s working memory.
Afterwards, once the domain expert accepts the extended plausible justification, the
inferences will be materialized in the knowledge base.
4 Implementation Details
Our system currently relies on Prolog to realize deductive reasoning, and to perform
the unification steps during analogical reasoning. Our system further employs Aleph 1
(A Learning Engine for Proposing Hypotheses), an Inductive Logic Programming (ILP)
system, to realize analogical reasoning. Custom Java code implements the conceptual
similarity check discussed in Section 3.2.
Regarding the expert system’s Semantic Web layer, we utilize the well-known
Apache Jena framework to apply OWL reasoning on incoming RDF data. Conversion
from RDF triples to Prolog and back is performed by custom Java code. Similarly, we
wrote Java code to convert SPIN rules to Prolog, utilizing the Topbraid SPIN API. The
user interface was implemented using the javax.swing packages, and utilizes the
Prefuse graph library for visualizing the justification trees and concept hierarchies.
5 Related work
To deal with incomplete (and partially incorrect) knowledge bases, Tecuci et al. [7,
10] employs justification trees to integrate inferences from multiple learning
mechanisms. A three-step, tutor-based approach is suggested, ending with a sufficiently
complete knowledge base ready for querying. Instances of justification trees, based on
positive training examples and verified by a human tutor, are generalized and added to
the knowledge base; allowing future similar inferences to be deductively entailed. Next,
other instances are found and verified by the tutor, whereby positive and negative
instances are used to fine-tune generalized justifications. Finally, inconsistencies (i.e.,
negative instances) are resolved by eliciting new knowledge (e.g., concepts). In contrast
1 http://www.cs.ox.ac.uk/activities/machlearn/Aleph/aleph.html#SEC1
to Tecuci et al., our goal is not to exhaustively extend a knowledge base until it is ready
for querying. Instead, an important aim is to supply plausible justifications for
individual queries on a case-by-case basis. For instance, in our medical use case,
domain experts (e.g., physicians) need to be acutely aware of the rationale behind every
diagnosis or drug recommendation, including any related deterministic or plausible
inference. In addition, we provide the domain expert with the choice to materialize and
fine-tuned plausible justifications in the knowledge base; allowing these inferences to
be deductively entailed in the future. In our work, we illustrated how semantic
technology can improve this kind of approach. We note that, regarding OWL reasoning,
Horridge et al. [16] discuss efficiently obtaining justifications for OWL entailments.
Fuzzy, probabilistic or possibilistic learning methods for dealing with uncertainty
could be applied to further supplement justification trees (or initial knowledge bases).
A number of works have studied specification and reasoning under uncertainty in OWL
[17, 18]. However, as opposed to such learning methods, we note that inferences from
inductive and analogical reasoning can be straightforwardly presented to domain
experts. Studying the integration of such learning methods in our expert system, while
still supplying useful explanations to domain experts, is considered future work.
6 Conclusions & Future work
In this paper, we illustrated a multi-strategy reasoning approach for enhancing query
access to medical knowledge bases. As opposed to traditional Semantic Web reasoning,
based on a priori deterministic knowledge, this approach additionally leverages data
similarities as well as plausible knowledge. In particular, our Semantic Web expert
system supplies plausible query explanations to medical experts, by complementing
deterministic reasoning with plausible inferences from analogical and inductive
reasoning. We illustrated the usefulness of our system by a real-world, medical use
case, which, in light of incomplete knowledge, involved applying both deterministic
and plausible knowledge. Based on their real-world expertise, domain experts can
confirm plausible justifications, and fine-tune the resulting deterministic knowledge.
Finally, we showed that weak inferencing can benefit from Semantic Web technology
as well, by improving similarity checking and expressivity of plausible knowledge.
Future work consists of applying additional learning methods, and studying how
their uncertainty results may be reflected in plausible justifications in a way that is
straightforward for domain experts to understand. In the same vein, we aim to associate
logical proofs with generated inferences; for instance, reflecting the inferencing steps
responsible for inferred knowledge. Based on these “traces”, domain experts could
choose to manually revert unsuitable materializations for certain entities. Additionally,
we plan to run experiments with a large medical dataset, to study the impact of our
integrated, multi-strategy reasoning approach on performance.
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