ELMO: AN INTEROPERABILITY ONTOLOGY

FOR THE ELECTRICITY MARKET

Panos Alexopoulos, Konstantinos Kafentzis

IMC Technologies S. A., 47 Fokidos Str., 11527, Athens, Greece

Christoforos Zoumas

Hellenic Transmission System Operator S. A., 22 Asklipiou Str., 14568, Krioneri, Greece

Keywords:

Ontologies, Semantic Interoperability, Electricity Market.

Abstract:

The liberalization of the electricity market in the European Union is a process of signiﬁcant importance that

aims at creating an efﬁcient deregulated internal electricity market within the Union. An important chal-

lenge towards that end is deﬁnitely the development of effective market mechanisms and regulations that will

comprise the operational framework of the market. Equally important, however, we consider the develop-

ment of an interoperability framework that will enable the effective and unproblematic interaction between

the market participants at both human and system level. Towards that direction we propose in this paper the

Electricity Market Ontology (ELMO), an ontological model that provides a shared, common understanding

of concepts and procedures regarding the electricity market operation. ELMO has been developed for the

Hellenic Transmission System Operator (HTSO) and it is currently used by the organization for providing

intelligent information access services to people interested in the market.

1 INTRODUCTION

The liberalization of the electricity market in the Eu-

ropean Union (Trevino, 2008), (Albers, 2001) is a

process of signiﬁcant importance that aims at creat-

ing an efﬁcient deregulated internal electricity market

within the Union (Boucher and Smeers, 2001). The

ultimate goal is to build a market that will make efﬁ-

cient use of resources and which, through free com-

petition, will be able to guarantee reasonable prices

of electricity. Towards that end, and given the fact

that the electric energy sector in most EU countries is

monopolized by national authorities, an important re-

quirement for the successful operation of the market

is the effective and unproblematic interaction between

these authorities and the other market participants.

Facilitating such an interaction is primarily a mat-

ter of ensuring interoperability within the market, that

is ensuring that diverse people, organizations and in-

formation systems are able to work together in the

market operation context. For the ﬁrst two, interop-

erability can be achieved through the development of

a commonly accepted market operational framework

that everybody understands and implements. For in-

formation systems, however, to do that, semantic in-

teroperability is required.

Semantic interoperability is achieved when the

meaning of exchanged information is understood by

applications and services. For that to happen, the in-

formation must be represented in a format that con-

veys its meaning in an unambiguous and machine-

interpretable way. To that end, ontologies can play

a vital role.

An ontology is “a formal explicit speciﬁcation of

a shared conceptualization for a domain of interest”

(Gruber, 1993). As such, it is a way of dealing with

ambiguity and heterogeneity in a domain by repre-

senting the meaning of the domain’s terms through

high-level abstract concepts and corresponding se-

mantic relations between these concepts. Formality,

namely representation of the ontology by means of

some formal computer language, allows for machine-

interpretability of the domain’s semantics.

For that, we present in this paper the Electric-

ity Market Ontology (ELMO), a semantic model that

provides a shared, common understanding of con-

cepts and procedures regarding the operation of the

electricity market. The ontology was primarily de-

veloped for the electricity market of Greece and ac-

cording to the Greek legislative framework (Hellenic

Ministry of Development, 2005). Nevertheless, the

Alexopoulos P., Kafentzis K. and Zoumas C. (2009).

ELMO: AN INTEROPERABILITY ONTOLOGY FOR THE ELECTRICITY MARKET.

In Proceedings of the International Conference on e-Business, pages 15-20

DOI: 10.5220/0002226400150020

 SciTePress

latter’s conformance to the corresponding EU frame-

work (EU, 2003), the fact that member states have

similar market architectures and the generic character

of the ontology’s structure and content allow, in our

opinion, the ELMO ontology to act as as the basis for

the development of similar ontologies for the markets

of the other EU countries.

Given the above, the structure of the rest of the

paper is as follows: In the next section we describe

the development approach we followed while in sec-

tion 3 a high-level description of the ontology’s struc-

ture and content is provided. In section 4 we give de-

tails on how the Hellenic Transmission System Oper-

ator used the ELMO ontology for providing the pub-

lic with semantic-enabled access to market relevant

knowledge and in section 5 we summarize the key

aspects of our work and we discuss potential future

work.

2 OVERVIEW OF OUR

APPROACH

The development of the ELMO ontology was part

of a project involving the development of an elec-

tronic library for HTSO, the Transmission Sys-

tem Operator of Greece. The library, which is

currently deployed and available through the URL

http://emarketinfo.desmie.gr/htso/user, was to contain

documents relevant to the operation of the electricity

market and to provide its users access to this content

through semantic-enabled search and navigation ser-

vices.

The ontology’s role within the library was to sup-

port these services by capturing and encoding the con-

tent’s semantics which, given the nature of the doc-

uments, were in principle the semantics of the elec-

tricity market domain. Nevertheless, the development

process of the ELMO ontology was mainly domain-

oriented rather than application-oriented and had as

key objective the construction of an extensible and

highly reusable knowledge model that could be used

by organizations such as HTSO as:

• The backbone of any knowledge repository that

stores market relevant knowledge.

• A comprehensive starting point for develop-

ing specialized ontologies and corresponding

ontology-based applications that serve market-

speciﬁc tasks.

• An ontological framework based on which the or-

ganization’s market related information systems

could semantically interoperate with similar sys-

tems of other organizations.

Given the above, one of the key decisions in de-

signing the ELMO ontology was to deﬁne it through

a multi-layered architecture that would effectively

divide it into highly maintainable, extendible and

reusable modules. More speciﬁcally, when a large-

scale ontology is composed out of smaller ones then

its development and maintenance are easier and more

efﬁcient. At the same time, when the independent

parts of the ontology are well deﬁned and separated

then it is highly possible that these parts can be reused

in other similar applications. Finally, a layered archi-

tecture makes it far easier to extend the ontology so

that it can cover application domains other than the

existing ones.

In the case of the ELMO ontology, the basic layer-

ing criterion was the geographical applicability range

of the ontology’s knowledge. More speciﬁcally, as

mentioned before, the ontology was primarily devel-

oped for the electricity market of Greece and there-

fore it was bound to contain knowledge that was valid

only for this country. On the other hand, Greece, as all

other member states of the EU, has already adopted

and incorporated to its legislation the Electricity di-

rective 2003/54/EC, which is the key European legis-

lation to establish the Internal Market of Electricity.

As such, a great part of the ontology was expected

to refer to knowledge that was applicable to all EU

countries. Separating, by means of different layers,

this EU-speciﬁc knowledge from the Greece-speciﬁc

one within the ELMO ontology yields, in our opinion,

a number of signiﬁcant advantages including:

• Easier ontology maintenance as the two legisla-

tive frameworks might change at a different rate

and way.

• Ability to use the EU-speciﬁc layer as an upper

ontology for the development of market ontolo-

gies for other EU countries.

• Easier mapping between the ELMO ontology and

other existing country-speciﬁc market ontologies.

Given the above, the architecture of the ELMO

ontology consists of ﬁve layers, as depicted in ﬁg-

ure 1. The two dotted-lined layers are not currently

implemented but they will be in the future. The sep-

aration of the rest three layers reﬂects, apart from the

usual abstraction criterion, the aforementioned geo-

graphical applicability range criterion as well. In the

following section an analytical description of all ﬁve

layers in terms of structure and content is provided.

Finally, it should be noted that the ELMO on-

tology is formalized using OWL (Bechhofer et al.,

), since it is a standard language for repre-

senting ontologies on the web, and it has been

developed using the open source ontology edi-

ICE-B 2009 - International Conference on E-business

tor Prot

e (http://protege.stanford.edu). Further-

more it has been successfully checked for in-

consistencies using the Pellet OWL DL Reasoner

(http://clarkparsia.com/pellet).

Figure 1: ELMO Layered Architecture.

3 THE ELMO ONTOLOGY

LAYERS

3.1 Generic Market Independent Layer

An important design decision in developing ELMO

ontology was whether we should deﬁne an upper on-

tology, namely an ontology that covers generic and

domain-independent concepts.

In general, an upper ontology provides a starting

point, a predeﬁned set of ontological entities and an

ontology design pattern for building new, lower-level,

domain ontologies. Foundational ontologies such as

SUMO or DOLCE (Gangemi et al., 2002) comprise

natural candidates for the role of an upper ontology

as they have been developed exactly for this purpose.

However, choosing the best ﬁtting foundational ontol-

ogy from about a dozen freely available ones world-

wide is a very difﬁcult and time-consuming task while

in many cases it might be necessary to create custom

foundational ontologies by combining existing ones.

In the case of the ELMO ontology, we recognized

the advantages of having an upper ontology, yet time

and resource limitations made us postpone the pro-

cess of evaluating, selecting and perhaps customiz-

ing some existing foundational ontology for a future

project. In any case, we considered as a ﬁrst layer of

the ELMO ontology architecture the Generic Mar-

ket Independent Layer which is going, in the future,

to contain any upper ontology we choose to create or

reuse.

3.2 Generic Market Speciﬁc Layer

Given the absence of an upper ontology in the ELMO

architecture, the respective role can be assumed to

play the second layer, namely the Generic Market

Speciﬁc Layer (2). This practically deﬁnes the more

abstract market-related concepts and relations of the

ontology which are made more concrete in the lower

level layers.

More speciﬁcally, the layer comprises eleven con-

cepts (modelled as OWL classes) which are interre-

lated through ten relations (modelled as OWL object

properties). These are:

• Classes

– Market Process: Refers to any process or pro-

cedure that is part of the overall operation of the

electricity market.

– Market Participant: Refers to individuals and

organizations that play some role within the

market.

– Market Action: Refers to actions performed

by market participants in the context of speciﬁc

market processes.

– Market Right/Obligation: The two classes re-

fer to rights and obligations of the market par-

ticipants in the context of the market operation.

– Market Rule: Refers to rules that govern the

operation of the market.

– Market Unit/System: The two classes refer to

equipment, facilities and systems that are used

in the context of the market operation.

– Market Speciﬁcation: Refers to standards

and speciﬁcations that characterize the market’s

systems and units.

– Market Information Source: Refers to any

piece of market related information such as

manuals, document templates, archives, reg-

istries etc.

– Market Extent: Refers to parameters, data,

factors, elements and virtually any extent that

is relevant with the electricity market.

ELMO: AN INTEROPERABILITY ONTOLOGY FOR THE ELECTRICITY MARKET

Figure 2: ELMO Generic Market Speciﬁc Layer.

• Object Properties

– participatesIn(Participant, Process): Links

market participants with the processes they par-

ticipate in.

– isPerformedBy(Action, Participant): Links

market actions with the participants that they

perform them.

– isPerformedInTheContextOf(Action, Partici-

pant): Links market actions with the processes

they are part of.

– regardsProcess(Right t Obligation t Rule,

Process): Links rights, obligation and rules

with the processes they refer to.

– concernsParticipant(Right t Obligation,

Participant): Links rights and obligations

with market participants.

– isUtilizedIn(Information Source, Process):

Links information sources with the processes

they play some role in.

– isFoundIn(Extent, Information Source):

Links extents with information sources they

are referred within.

– hasSpeciﬁcation(Unit t System, Information

Source): Links units and systems with their re-

spective speciﬁcations.

– isPartOfProcess(Process , Process): Links

processes with the sub-processes that might

comprise them.

– isPartOfAction(Action , Action): Links ac-

tions with the sub-actions that might comprise

them.

The above conceptualization schema provides, in

our opinion, a comprehensive and adequately abstract

view of the market as almost all interactions that may

take place within it and in the context of its operation,

can be represented by specializing or instantiating the

components of this schema. Furthermore, the delib-

erate absence of electricity and energy related knowl-

edge from this layer of the ELMO ontology allows the

ﬁrst to be potentially reused as an upper ontology for

other markets as well.

3.3 International Market Speciﬁc Layer

The international market speciﬁc layer is supposed

to contain market-related knowledge that is valid

and applicable for all the electricity markets of the

world. Such knowledge is already contained within

the ELMO ontology, however, since currently there

is no formal activity towards a common international

electricity market exists, the task of extracting in-

ternationally applicable knowledge is quite difﬁcult.

Therefore, the ELMO ontology does not currently im-

plement this layer but includes it in its architecture so

that it can implement it in the future.

3.4 EU and Greek Market Speciﬁc

Layers

The EU and Greek market speciﬁc layers are the rich-

est, in terms of content, layers of the ontology as they

contain about two thousand classes and instances and

about seven hundred asserted instantiated object prop-

erties. These, as suggested in the previous section,

are either instances or specializations of the generic

layer’s components. As a result, the two layers com-

prise overall a number of class hierarchies, instance

taxonomies and, of course, instantiated binary object

properties.

An example of a class hierarchy is the one derived

by subclassing the Market Participant class. A rep-

resentative snapshot of this hierarchy is the following:

ICE-B 2009 - International Conference on E-business

• Producer

– Dispatchable Unit Producer

– Contracted Unit Producer

– Cold Reserve Unit Producer

– New Generation Unit Producer

– Auto Producer

• Load Representative

• Meter Representative

• Transmission System Operator

• Production Licence Holder

– Production License Holder of Contracted

Hydro Unit

– Production License Holder of Black Start

Unit

Similarly, an example of an instance taxonomy is

the one derived by relating the instances of the Mar-

ket Process class through the isPartOfProcess object

property. A representative snapshot of this taxonomy

is the following:

• Registration with the ENERGY TRANSAC-

TIONS SYSTEM

– Registration with the Participant Register

– Conclusion of Energy Transactions Contract

• Daily Ahead Scheduling

– Submission of Load Declarations

– Energy Offer Submission

• Dispatch Procedure

– Dispatch Schedule preparation

– Issue of Dispatch Instructions

• Imbalances Settlement

– Calculation of Energy Deviations

– Generation Deviations Settlement

• Meter and Measurement Administration

– Meter and Meter Representative Registra-

tion

– Metering Data Adaptation

• Ancillary Services and Supplementary System

Energy

– Supplementary System Energy Provision

– Remuneration in the context of Cold Reserve

Contracts

• Capacity Assurance Mechanism

– Unforced Capacity Table Preparation

– Issue of Capacity Availability Tickets

In general, deciding whether the specialization of

an ontology’s concept should be performed by means

of subclassing or instantiation, depends on the domain

of the ontology, the application scenario the ontology

is utilized within and the application speciﬁc reason-

ing that is performed on the ontology. In the case of

the ELMO ontology, we made every effort to take in

mind only the domain and not so much the application

scenario (which was semantic information retrieval)

or its reasoning mechanism (which required almost

all concepts to be treated as instances).

As far as the distinction between EU-speciﬁc and

Greece-speciﬁc concepts is concerned, this was per-

formed on the basis of the knowledge we were able

to extract from the relevant EU legislation docu-

ments we had access to. Additionally, many concepts

were “giving away” their nationality directly through

their name (e.g. “Unit under Article 35 of Law

2773/1999” or “Hellenic Transmission System Op-

erator”).

In any case, in order to avoid any inaccuracies

within the ontology, we initially considered all mar-

ket speciﬁc concepts to belong to the Greek layer and

then we began methodically to move concepts to the

EU layer. At the moment, this task is still ongoing

and we expect that the next versions of the ELMO on-

tology will comprise a much richer EU-speciﬁc layer

than the current one.

4 USAGE OF THE ELMO

ONTOLOGY

The ELMO ontology is currently utilized within the

Hellenic Transmission System Operator as a vital

component of the organization’s electronic library, a

semantic-enabled knowledge portal that provides the

public with effective and efﬁcient access to knowl-

edge regarding the Greek electricity market.

More speciﬁcally, the available knowledge com-

prises market-related documents which, due to their

size and the lack of proper cross referencing, are dif-

ﬁcult for an individual to understand and use. The

system tackles the two problems by enabling the stor-

age and retrieval of decomposed parts of the doc-

uments (usually paragraphs) as well as navigation

across these parts. These services are semantic-

enabled in that the system implements them by uti-

lizing the ELMO ontology for capturing and inter-

relating the parts’ semantic content. This allows for

signiﬁcantly more effective information retrieval, in

terms of results relevance, as well as for more intuitive

navigation across the content through the ontology’s

semantic structures such as concept taxonomies.

ELMO: AN INTEROPERABILITY ONTOLOGY FOR THE ELECTRICITY MARKET

Figure 3: HTSO Electronic Library.

The system was deployed and made available

to the public in October 15th 2008 through the

URL http://emarketinfo.desmie.gr/htso/user (ﬁgure

3). From there one can examine a representative part

of the ELMO ontology by using the available tax-

onomies for content navigation.

5 CONCLUSIONS & FUTURE

WORK

In this paper we presented the Electricity Market On-

tology (ELMO), a semantic model that provides a

shared, common understanding of concepts and pro-

cedures regarding the operation of the electricity mar-

ket. The ontology, though primarily developed for

the Greek electricity market, may in our opinion act

as an ontological framework based on which similar

ontologies for the markets of the other EU countries

can be developed as well. This is supported by two

key facts: First that the knowledge the ontology con-

tains conforms to the EU legislative framework for

the electricity market and second that its architecture

is a multi-layered one thus allowing a high degree of

extensibility and reusability.

As a future work we intend to continue working on

the enrichment of the ontology’s EU-speciﬁc layer so

as to separate it totally from the Greek one and make

it highly reusable for other markets as well. Further-

more, we are going to examine the suitability and ap-

plicability of several foundational ontologies for our

Generic Market Independent Layer and, if necessary,

deﬁne a custom upper ontologies that will serve our

objectives best. Finally, we shall investigate a number

of application-speciﬁc enhancements to the ontology

in order to make it directly usable to several market-

related applications.

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