April 23, 2021 1

Using formal thesauri and controlled vocabulary as the 

interface between the unstructured data and axiomatic 

ontologies

Farhad Ameri

NIST TLP COI Event

April 2021, Gaithersburg, MD 
April 23, 2021 2

High-level Research questions 

• Supply Chain Use Case :

• Data type: Manufacturing Capability data 

• Data source: company website

• Maintenance Use Case : 

• Data type: MWO records

• Data Source: CMMS

How Knowledge Organization Systems (KOS) can 

be used in an integrated fashion to support 

formal knowledge extraction from unstructured 

data? 
April 23, 2021 3

Maintenance Use Case Objectives 

• To expose and formalize the semantics of unstructured 

maintenance data. 

• To visualize MWO records as RDF knowledge graphs 

• To use RDF knowledge graphs for maintenance diagnostics and 

root-cause analysis.
April 23, 2021 4

Knowledge Organization Systems (KOS)

• Knowledge organization system is any 

system of terms or scheme that is created 

to organize, manage, and retrieve 

information.

• They vary in complexity, structure, function, 

and expressivity.

• Services:

• Abstraction & Indexing 

• Tagging 

• Information retrieval and term disambiguation

• Navigation and translation 

• Reasoning and inference 

term lists

synonym rings

name authorities

taxonomies

thesauri

glossaries

dictionaries

gazetteers

categorization schemes

classification systems

subject heading schemes

semantic networks

ontologies 

Source: Introduction to taxonomies and other knowledge organization systems, Heather Hedden and Helmut Nagy, Semantic Web Company 

KOS Types

Controlled 

vocabulary for 

Information 

Retrieval 
April 23, 2021 5

Expressivity

Development Cost / Time

Semantic Spectrum of Knowledge Organization Systems

Term 

List

Informal 

Hierarchy 

Thesaurus 

Taxonomy 

Conceptual 

Model 

Ontology

OWL, KIF

RDFS, UML

RDF/RDFS

SKOS

XML

Glossary, Dictionary, 

Controlled Vocabulary 

Semantic interoperability

Syntactic/Structural 

interoperability Name 

Authorities 
April 23, 2021 6

Thesaurus 

• A controlled vocabulary that represents three type of relationships 

between terms or concepts: 

• Hierarchical: broader term/narrower terms 

• Associative: related terms 

• Equivalence: preferred label /alternative label

• Created in accordance with standards: 

• ISO 25964 (2011, 2013) and ANSI/NISO Z39.19 
April 23, 2021 7

SKOS model (Simple Knowledge Organization System)

SKOS is a standard data model for representation of knowledge organization systems. 

• W3C Standard

• Web-native syntax

• Encoded using XML/RDF 

• Each concept has a unique URI

• Machine-readable

• Simple semantics Oxidation

Chemical Reaction

Homolytic Oxidation

Heterolytic Oxidation

SKOS:Broader

SKOS:Narrower

Coating

Rust

Galvanization

SKOS:Related

SKOS:AltLabel Rusting

Oxidation is the loss of electrons during a 

reaction by a molecule, atom or ion.

SKOS:Definition

Equivalence Relationship 
April 23, 2021 8

Why Thesaurus? 

Thesaurus 

They can accommodate large or constantly growing vocabulary 

They can be used to directly tag unstructured data

They are easier to develop and extend compared to ontologies 

High level expressivity and 

formality 

Logic-based semantics

Lexical semantics

Ontology Thesaurus 

Ease of extension 

We want to use the best of both worlds
April 23, 2021 9

Expressivity

Development Cost / Time

Overall Approach: Incremental structuring and semantic 

enrichment process

Thesaurus 

Ontology

RDF Triples

SKOS Intermediary

concept model 
April 23, 2021 10

Example

Solenoid valve on upper lift cyl

leaking. Hyd pressure reduced on 

Boom. Technician called. valve 

replaced, works normal

Artifact

Failure

Agent

Process

States

Raw text (portion of reality) from a MWO Record Explicit Entities Implicit Entities

Events
April 23, 2021 11

Ontological Representation of problem-solution description 

Solenoid valve on 

upper lift cyl

leaking. Hyd

pressure reduced 

on Boom. 

Technician 

called. valve 

replaced, works 

normal

<<< Ideal Situation >>>
April 23, 2021 12

2-step process: First annotate the text with SKOS concepts

Solenoid valve on 

upper lift cyl leaking. 

Hyd pressure 

reduced on Boom. 

Technician 

called. valve 

replaced works 

normal
April 23, 2021 13

Create an intermediary representation (structured)

Intermediary 

representation 

(Concept Model) 

Solenoid valve on 

upper lift cyl

leaking. Hyd

pressure reduced 

on Boom. 

Technician 

called. valve 

replaced works 

normal • Graph 

• Table 

Semantic Web Zone

SKOS, RFD/XML, RDFS. OWL
April 23, 2021 14

Maintenance Diagnostics Thesaurus 

A SKOS model for representation of controlled vocabulary in the maintenance domain. 

For this purpose, we developed Maintenance Diagnostics Thesaurus or MDT 
April 23, 2021 15

The scope of Maintenance Diagnostic Thesaurus (MDT) 

• Failures

• Treatment 

• Quality (color, temperature, 

viscosity, lumen)

• Feature (crack, hole, breakage)

• States

• Working, not working 

• Process 

• Malfunctioning (e.g., 

leaking, rotating slowly)

• Including not 

functioning or reduced 

functioning 

• Items

• Component

• Equipment/Machine

• Sub-system

Scope of MDT:
April 23, 2021 16

MD Thesaurus 

Top-level Thesaurus 
April 23, 2021 17

Entity Extractor 
April 23, 2021 18

Detected Concepts

Detected as skos:prefLabel

Detected as skos:altLabel
April 23, 2021 19

Exported Concept Model for the MWO record 

Exported Table 

Formats available:

• CSV 

• RDF/JSON
April 23, 2021 20

Thesaurus Development challenges 

• To adequately annotated all 

WO records even in a single 

company, we need a large 

thesaurus. 

• Thesaurus extension is a 

bottleneck 

• Mainly manual process 

• One concept at a time

• Batch import
April 23, 2021 21

Semi-automated Extension of MDT 

• Provides NLP Services

• Shallow taxonomy of 

terms 

• More complex Taxonomy

• Lexical and associative 

relationships 

CSV CSV or rj

RDF 

Triples

We

are

here 
April 23, 2021 22

Categorizing Items (from Nestor) in MDT 

Nestor Output (Item column)

Candidate 

Terms
April 23, 2021 23

Next Steps 

• Extending the thesaurus and ontology in tandem 

• Better integration with Nestor 

• More diverse dataset is needed to feed the thesaurus extension process 

• Tool Development :

• SKOS to OWL : Receives SKOS Concept Model and converts it to RDF graph 

• Reasoning to extract inferred knowledge (hidden / implicit)

• Diagnosis Tool: Provides diagnostic support by querying the RDF graph