Ontology: Its Transformation FromPhilosophy to Information Systems

Gloria L. ZWigaThe Acton Institute, 161 Ottawa NW, Suite 301, Grand Rapids, MI 49503

gzuniga@acton.org

Abstract - It is no secret that the mul t id isc ipl inary sphere of informat ion systems hasborrowed the term ‘ontology’ f rom phi losophy, and re in terpre ted i t to be more sui table forinformat ion systems. However , there is some disagreement about what th is re interpreta t ionshould be. This paper examines two prominent and distinct views on what informationsys tems onto logy i s , and a t tempts to advance a uni f ied def in i t ion tha t can be unders toodinterdisciplinarily. But the goal of this paper is to show the specific points of variancebetween in format ion sys tems on to logy and ph i losophica l on to logy in o rder to shed l igh t onthe transformation of the term ‘ontology’ in its adoption by the information systemscommunity. The rela t ively new information systems ontology is facing great chal lenges thatmay be be t te r conf ronted wi th the ins ights tha t can be d iscovered through phi losophica lontology.

Categories & Descriptors - H.0 [Information Systems]: General. 1.0 [ComputingMethodologies]: General. I. 1.1 [Symbolic and Algebraic Manipulation]: Expressions and TheirRepresentation - Representations (general), SimpliJcation of expressions. I. 1.3 [Symbolic andAlgebra ic Manipula t ion] : Languages and Sys tems - Evalua t ion s t ra teg ies . 1.2.0 [Artif icialIntelligence]: General ~ Philosophical jimndations. 1.2.4 [Artificial Intelligence]: KnowledgeRepresentation Formalisms and Methods -Relation systems, Representation languages.

General Terms - Design, Economics, Reliability, Human Factors, Languages, Theory.

Keywords - Ontology, Phi losophy, Descr ip t ion , Representa t ion , Informat ion Sys tems,Ontology of Information Systems.

1 . The Practical Significance of Distinguishing Information SystemsOntology and Philosophical Ontology

Unti l recent ly , the re la t ionship be tween informat ion sys tems and phi losophy wasanalogous to that between two distant countries, each with a distinct language and culture. Infact , the respect ive di rect ions of thei r invest igat ions appeared or thogonal f rom one another .Today, the scenario is different. It is, in fact, ontology - a branch of philosophy - that hasserved as the br idge for the coming together of informat ion systems and phi losophy. But thero le tha t onto logy seems to have in informat ion sys tems i s whol ly d is t inc t f rom i t s ro le inphi losophy. There are some disagreements in the information systems l i terature about whatontology is but, in short, it would be safe to say that information systems ontology is a formallanguage designed to represent a par t icular domain of knowledge. The purpose for most , i fnot a l l , in format ion sys tems onto logies i s fnnctional. In other words, an information systemsPermission to make digital or hard copies of all or part of this work for personal or classroom use isgranted without fee provided that copies are not made or distributed for profit or commercial advantageand that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, topost on servers or to redistribute to lists, requires prior specific permission and/or a fee.FOIS’OI, October 17-19,2001, Ogunquit, Maine, USA.Copyright 2001 ACM l-581 13-377-4/01/0010...$5.00.

187

ontology is designed for one or more specific purposes that arise in the effort to computerizeas much information as possible, an effort that characterizes today’s business and educationalenvi ronments .

In con t ras t to th i s , ph i losoph ica l on to logy i s ne i the r r educ ib le to , no r iden t i ca l wi thlanguage or i ts formalism, a l though i t employs the conceptual machinery of language as anins t rument of descr ip t ion . The targets for descr ip t ion are the th ings in themselves in anydomain, and the relat ions exist ing among them. For example, the ontology of economicobjec ts i s occupied wi th the descr ip t ion of i t s ob jec t s , such as money and pr ice , and the i rrelations as part of the (human) social world [21]. It is important to recognize that the targetfor representa t ion of an informat ion sys tems ontology is the conceptual background tha t i spresupposed in and cor responds to a descr ip t ion of a domain of ob jec ts , in addi t ion to thedescr ip t ion i t se l f . In th is sense , an informat ion sys tems onto logy i s a t leas t one leve l ofexplanat ion removed from the domain of physical or socia l objects that i s the subject of theinvestigation. More importantly, the goal of philosophical ontology is truth. This means thatcollecting the knowledge of the denizens of any sphere would not be sufficient to produce anontology of tha t sphere . Our knowledge, i f i t i s to be useful to us , must be ver id ica l or , a tleast, reasonably justified in relation to future events or other unknowable and non-verifiables ta tes of af fa i rs . Like informat ion sys tems ontology, phi losophica l ontology indeed accountsfor knowledge and the conceptual f ramework of the sphere under invest igat ion. However ,part of the task involves distilling true from false beliefs in the analysis of the nature of thesphere under investigation.

The term ‘ontology’ has become such an in tegra l par t of the specia l ized language ofinformation systems that , despi te the exis t ing array of interpretat ions, information systemsresearchers are for the most par t content wi th th is ambiguous status quo. I be l i eve th i s i scounterproduct ive. There is a pract ical s ignif icance to the effort of more clearly defininginformat ion sys tems onto logy, and d is t inguish ing i t f rom phi losophica l onto logy. Here a resome pract ical reasons. Firs t , i t has become a recent t rend in both industry and the academyto h i re ph i losophers , on to log i s t s in pa r t i cu la r , fo r the purpose o f deve lop ing on to log ies incollaboration with knowledge engineers and other specialists. The work that thesephilosophical ontologists perform ranges from the almost mechanical, such as sorting data bycategor ies , to the highly technical , such as programming. There is no general ly accepteddescr ip t ion for what on to log is t s a re expec ted to do and th i s s i tua t ion presen ts the po ten t ia leconomic problem of inefficient allocation and distribution of work. If the informationsystems people themselves cannot c lear ly and unders tandably communicate what ontology isto people ou ts ide o f the i r own sphere , those in charge of h i r ing wi l l a l so no t know how tobest seek for candidates, or how to best employ the human capital of a new ontologist hired.Second, there is a evident contrast between the multitude of user-specific informationsystems ontologies - for example, the Internet apparel retail ontologies for stores A throughZ - and the absence of general ontologies , such as a general ontology for In ternet apparelretail. ’ This sugges ts tha t informat ion sys tems is e i ther not equipped to advance genera lon to log ies , o r no t employing the r igh t methodology or theore t ica l approach to ach ieve th i s .There are great advantages to incorporating the framework of philosophical ontology into thepresent information systems research [17]. But this recognition will not occur until theinformat ion systems researchers are able to dis t inguish informat ion systems ontology f romphilosophical ontology. Finally, but not least importantly, although the level of programmingand software sophistication is rapidly increasing, the consensus outside of the academy seemsto be tha t informat ion sys tems, such as local ized databases , do not a lways meet the user’s

‘In [ 171, Smith considers the task of establishing a general ontology of world history. “This wouldrequire a neutral and common framework for all descriptions of historical facts, which would require inturn that all events, legal and political systems, rights, beliefs, powers, and so forth, be comprehendedwithin a single, perspicuous list of categories.” Later he observes “why the project of a common ontologywhich would be accepted by many different information communities in many different domains has thusfar failed.” The reason is, he says, “not all conceptualizations are equal.”

188

expecta t ions . These chal lenges can be , I be l ieve , bet ter confronted wi th the ins ights tha tphilosophical ontology can add to information systems ontology.

In the ensuing discussion, I will examine two distinct characterizations of informationsys tems ontology wi th an eye for f inding a common ground, as wel l as to se t t ing suchcharac ter iza t ions aga ins t the backdrop of phi losophica l onto logy. This examinat ion wi l lprovide the best forum to contrast philosophical ontology and information systems ontology,and to show the transformation of ontology as it crossed interdisciplinary boundaries.

1.1 Information Systems: the sphere of investigations visd-vis thesystems themselves

Before proceeding, however, we must make some necessary terminologicald is t inc t ions . The first d is t inct ion we shal l make involves the name ‘ informat ion sys tems’because it is potentially equivocal. On the one hand, it has been employed to denotegenerically those specialized investigations in disciplines such as computer science,linguistics, and cognitive science that fall under subject headings such as informationtechnology, knowledge representa t ion , and computa t ional l inguis t ics . Moreover , each ofthese subjects i s , i t se l f , const i tu ted by even more specia l ized f ie lds of inquiry . Informat iontechnology, for example, br ings together database theory, design, and management , as well asnetwork architecture. In addition to all this, it is also safe to say that information systems is are la t ive ly new area of ph i losophica l inqui ry . Ph i losophy too , then , mus t be added to theaforement ioned l i s t of d isc ipl ines occupied wi th informat ion sys tems. I t i s c lear that theinterdisciplinary composition of the sphere of information systems, combined with thespecia l ized nature of the mul t i tude of i t s f ie lds of inquiry , present enormous obstacles todemarcat ion.

On the other hand, the name ‘information systems’ is also employed to identifypar t icular informat ion systems. Consider that a par t icular database , a par t icular knowledgebase, and a par t icular sof tware appl icat ion for data processing, each can be referred to as aninformat ion system. In order to avoid any terminological confusions , I shal l refer to thesphere of invest igat ions as information systems, and I wil l employ the acronym IS for theparticulars that result from such investigations.

1.2 Ontology: the sphere of investigation vis-kvis the particularontology

One addi t ional d is t inc t ion remains to be made , tha t be tween onto logy as a sphere ofinves t iga t ion , and a par t icu la r on to logy tha t resu l t s f rom an on to log ica l inves t iga t ion . Theformer is the branch of philosophy occupied with the description of existence and reality. Thela t te r i s e i ther someone’s onto logy , or an onto logy of th i s or tha t domain of ob jec ts - forexample Husser l ’s formal ontology, or an ontology of works of ar t . In what fol lows, I shal lc lear ly ident i fy whether I am referr ing to the former or to the la t ter . Let us begin, then, byconsider ing two of the most prominent def in i t ions of an IS ontology in the informat ionsystems literature.

2. Definition One: An Ontology is an Explicit Specification of aConceptualization

According to Thomas Gruber, “An ontology is an explicit specification of aconceptualization” [5]. Here, the subject is a particular IS ontology, and not the philosophicalsphere of ontological investigations. However, in order to understand this definition of an ISonto logy, we must first unrave l the under ly ing assumpt ions tha t concern on to logy properfrom those that concern the development of IS ontologies. Gruber states that, in philosophy,the term ‘ontology’ signifies a systematic account of existence [5]. If this means aclassification of entities, then this rough characterization of philosophical ontology isacceptable , a l though for an interdiscipl inary audience i t requires more c lar i f icat ion. The

189

distinction between formal ontology and material ontology is important to raise here. Formalontology consists in the general investigation and description of the properties of objects inthe world and the relations existing between different sorts of objects [8, 11, and 131.Mater ia l on to logy, by cont ras t , i s occupied wi th only a par t icu lar domain of objec ts , and i tcons is t s in the descr ip t ion of the s t ruc ture of the domain and the re la t ions of the objec tsthere in . There i s another d is t inc t ion tha t we must now cons ider : tha t be tween the word‘formal’ meaning general , and the word ‘formal’ in the sense of a deduct ive system and i tssymbolism. The latter meaning is the one most often used in the information systemscommunity, but it is the former meaning of the word ‘formal’ that applies to formal ontology.Once again, the relevant sense of ‘formal’ for ontology addresses the fact that the descriptionresu l t i ng from the inves t iga t ion i s genera l and thus appl icab le to a l l mater ia l spheres ordomains of reality [ 1 I]. Consider, for example, the following formal description (in the sensejust explained) of the different sorts of objects in the world. There are natural, independentlyex is t ing , phys ica l en t i t i es , such as the Grand Canyon, t igers , and tu l ips . Addi t iona l ly , thereare subject ive ent i t ies , such as pains , whose mode of exis tence depends on being fe l t byagents. There are also physical artefacts, such as tables and chairs, whose existence asfurni ture i s dependent on conceivers and the i r percept ions concerning the funct ion eachserves . We a lso f ind soc ia l ob jec ts in the wor ld , such as money, which i s cons t i tu ted bybel iefs , a l though tokens of money may be ins tant ia ted phys ica l ly and even e lec t ronica l ly .And there are also abstract entities, such as the color red and the number five, whose being isabstracted from particulars in the world. This general description is, arguably, a formalontology of existing entities. And we may apply the properties ‘subjective,’ ‘dependent’ and‘artefact’ in the descript ion of a mater ial ontology such as , for example, the sphere of socialobjects, or even in the more narrow sphere of economic objects [21].

Now the question is, what sorts of entities belong to the domain of informationsystems? Gruber juxtaposes the broad scope of entities that constitute reality in philosophicalontology with what appears to be a more restricted notion of existing entities applicable to ISontologies. Regarding the latter, he says, “what “‘exists”’ is that which can be represented”[5]. This representat ion is done by means of a formal language designed to accommodate aspecific vocabulary or protocol. Gruber thus appears to suggest that the entities that belong tothe domain of information systems are only those entities whose descriptions lend themselvesto representa t ion via symbol ism. I f th is i s t rue , then formal izat ion techniques wi l l determinewhat will be represented as existing in the relevant domain. The problem is that someexisting objects might be difficult to represent by means of a formal language. Oneproblematic case, for example, might be presented by the at tempt to represent the domain ofpsycholog ica l ob jec t s , such as psycholog ica l s t a tes . How would love , anguish , anx ie ty ,elation, loss of dignity, or any other psychological states be represented by means of a formallanguage? We must a lso ask the more fundamenta l ques t ion: Can a l l tha t i s descr ibable inph i losophica l on to logy a l so be represen ted in IS on to log ies? These ques t ions , howeverinteresting, will have to remain as open questions for now.

Let us tu rn our a t ten t ion ins tead to the descr ip t ive ro le of on to logy , bo th formal andmater ia l . The chief goal of phi losophical ontology is to advance a fa i thful descr ip t ion; ino ther words , to seek t ru th . The usua l approach to mater ia l on to log ica l inves t iga t ions i s toparcel the world according to domains of objects. It is important to point out that theparceling is not done arbitrarily. In other words, the parceling criterion is not perspectival inthe sense of assuming the point of view of some individual and his attitudes about the world.Ins tead , the parce l ing of the wor ld resul t s f rom the onto logica l inves t iga t ion i t se l f , whichaims to discover the natural joints separating distinct material spheres of reality, or domainsof objects.

But i s th i s k ind of non-arb i t ra ry parce l ing by domains of ob jec t s what i s involved inthe demarcation of a particular realm for an IS ontology? The term ‘conceptualization’appears to be relevant here. A conceptualization, Gruber says, is constituted by “the objects,concepts, and other entities that are assumed to exist in some area of interest and the

190

relationships that hold among them.“2 An important consideration in this regard concerns thecri ter ion employed for carving out the area of interest f rom that par t of real i ty that can berepresented. The significance of this turns on the fact that an IS ontology must account for theintended meaning of a formal vocabulary or protocol for a set of agents whose knowledge isrepresented by such forma1 vocabulary or protocol . Accordingly, the demarcat ion cr i ter ionwould have to be established, at least in principle, by the agents of the relevant sphere. Morespecifically, the agents’ knowledge of their sphere is tantamount to the conceptual frameworkof the sphere, which will reveal the nature, structure, objects, relations, and boundaries of thesphere . In theory , th is could be a sa t i s fac tory explanat ion of how a conceptual iza t ion i sobtained. Practically, however, Gruber presents a different story. He writes, “Aconceptual iza t ion i s an abs t rac t , s impl i f ied v iew of the wor ld tha t we wish to represent forsome purpose” [5]. I t seems, then, tha t a conceptual iza t ion is not a t the mater ia l level ofth ings , objec ts , and happenings . I t i s not even a t a genera l leve l where formal onto logyres ides . Rather , a conceptual iza t ion is a l ready a t leas t two levels of explanat ion removedfrom the material. A conceptualization is, instead, at a level of abstraction, simplification, andsymbolism.

Let us recall that Gruber defines an IS ontology as an explicit specification of aconceptua l iza t ion . Another way to unders tand th i s would be to say tha t an ax iomat ic theoryspeci f ies the conceptua l iza t ion expl ic i t ly . In o ther words , the IS onto logy i s the ax iomat ictheory expressed in some formal language that serves as the vehicle to express aconceptualization. What is not clear is what conceptualization is being expressed: the lowerlevel conceptual framework of the agents in the relevant sphere, or the higher levelabstraction that, presumably, is distilled from the lower level. If the latter, then the questionis : who does the d i s t i l l a t ion and abs t rac t ion? But , more impor tan t ly , how i s the abs t rac t ionmade? One poss ib i l i ty i s tha t the researchers involved become as famil iar wi th the re levantsphere as its denizens. This does not appear to be the standard procedure in the design of ISontologies . The other poss ib i l i ty i s tha t the researchers opt for a more gener ic approach thatdemands some arbitrariness. For example, the researcher obtains information from s tandardsurvey forms and questionnaires which, in turn, he uses for the formulation of aconceptualization. The next step would be the simplification of this rough formulation of theconceptualization, followed by the articulation of the axiomatic theory in some formallanguage. This is the IS ontology according to the view that Gruber provides. If the ISontology offers a faithful account of the intentional content of the relevant formal vocabularyor protocol, then we can say that the ontology adheres to its ontological commitment.According to Gruber , “an ontological commitment is an agreement to use a vocabulary ( i .e . ,ask questions and make assertions) in a way that is consistent (but not complete) with respectto the theory spec i f ied by an on to logy” [6]. I t i s not c lear , however , where the absence ofcompleteness lies. Nonetheless, we are clear on one point: the criterion for the demarcation ofa par t icular rea lm for an IS ontology is whol ly d is t inct f rom the non-arbi t rary parcel ing ofdomains of objects in philosophical ontology.

We are now ready to res ta te Gruber’s def in i t ion of an IS ontology in more access ib lelanguage in light of the foregoing discussion, We could say that an IS ontology is aformalization that represents a domain of objects and their relations. The conceptualization ofthis domain of objects is more difficult to clarify. It appears that, for Gruber, aconceptualization could be characterized as an abstract entity whose being is abstracted fromthe assumpt ion that there are ideas d ispersed in the minds of the agents of the re levantdomain that , i f harnessed, the abs t rac t whole could s tand for the ent i re domain. Perhaps th isis the reason why a conceptualization need not be explicit, but assumed from ouracquaintance with our own ideas and with how these ideas stand for things in the world. This,

2 Gruber attributes his notion of ‘conceptualization’ to that established by Michael Genesereth and N. J.Nilsson in their (1987) Logical Foundations of Artificial Intelligence.

191

however , i s jus t a specula t ion . Le t us now cons ider another def in i t ion of an IS onto logywhich will shed more light on our examination.

3. Definition Two: An Ontology is a logical theory accounting for theintended meaning of a formal vocabulary

Before advancing his own definition of an IS ontology, Nicola Guarino first considersthe accepted interpretation of the term ‘ontology’ in information systems. In its mostprevalent use, he explains, an IS ontology is “an engineering artifact, constituted by aspecific vocabulary used to describe a certain reality, plus a set of explicit assumptionsregarding the intended meaning of the vocabulary words” [4]. A better definition, he believes,is the following: “An ontology is a logical theory accounting for the intended meaning of aformal vocabulary” [4]. This def in i t ion , he says , “refines Gruber’s definition by making clearthe difference between an ontology and a conceptualization” [4]. As we shall recall, Gruber’sdef in i t ion of an IS onto logy i s “a spec i f ica t ion of a conceptua l iza t ion .” Guar ino objec ts toth is def in i t ion because the te rm ‘conceptua l iza t ion’ conta ined in th i s def in i t ion re fers to

ordinary mathemat ical or extensional re la t ions on the domain.3 He wr i t e s , “ these re l a t ionsreflect a particular state of affairs: for instance, in the blocks world, they may reflect aparticular arrangement of blocks on the table” [4]. The problem, according to Guarino, is thatGruber ’ s de f in i t ion does no t p rov ide an in tens iona l (wi th an “s” ) accoun t o f the no t ion o fconceptualization. “For instance,” he explains, “the meaning of the “‘above”’ relation lies inthe way it refers to certain couples of blocks according to their spatial arrangement.”

This distinction between extension and intension (with an “s”) has traditionallyconcerned expressions. On the one hand, two different expressions may apply to the samething. Hence, they have the same extension. Consider the expressions, “the capital ofFrance,” and “the City of Light” ~ both expressions apply to Paris. On the other hand, eachof these expressions br ings to mind a different perspect ive of Paris . “The capi ta l of France”br ings to mind a pol i t ica l perspect ive of Par is as the off ic ia l seat of the French government ,whereas “ the Ci ty of Light” br ings to mind a romant ic perspect ive of the c i ty’s beauty a tn igh t . Consequent ly , these express ions have two d is t inc t in tens ions . Guar ino’s concern maybe that if we ground an IS ontology upon criteria specific to the meaning of particularpredicate expressions or declarative sentences, then the IS ontology will be unable toaccommodate any other descr ip t ions that apply to the same th ing. I f we imagine Guar ino’sobjection set against our illustration, he might say that an ontology of Paris needs a criterionbroader than a s ta te of af fa i rs depic t ing only one aspect or perspect ive of Par is . I t i s thusimportant , Guarino argues, to account for the intensional re lat ions of the terms in a formalvocabula ry .

Let us see how intensional relations help to solve the problem we have just illustrated.Guar ino expla ins tha t , when the extens ion of a conceptual iza t ion i s v iewed as a s ta te ofaffairs, this has been represented as a structure <D,R>, where D is a domain and R is a set ofrelevant relations on D. Instead of this, he suggests that intensions or meanings of aconceptualization can be represented “as functions from possible worlds into sets” [4]. In thiscase we would have a s t ructure <D,W>, where D is a domain space and W is a set of a l lpossible worlds, or all possible states of affairs, on D. Suppose, then, that D is a set of threetennis balls on a flat surface, and W is the set of all possible arrangements of these three balls.Fur ther suppose tha t one of the poss ib le s ta tes of af fa i rs i s descr ibable by the express ion“hor i zon ta l l i ne” , and another poss ible s ta te of af fa i rs i s descr ibable by the express ion“vertical line.” The extension for both of these expressions - i.e., what they denote - willbe the same geometric figure in all possible worlds: a straight line. We could suppose that, ineach case , the spat ia l a r rangement of the three ba l l s i s equivalent in the sense tha t the ba l l sneed only stand for three points on a line. However, the spatial arrangement is not identical in

3 Guarino points out that Gruber has been influenced by the definition advanced in 1987 by Geneserethand Nilsson, in Logical Foundations of Artificial Intelligence.

192

both cases and wil l be displayed different ly on the domain space. In one s ta te of affa i rs , thel ine i s hor izonta l and, in the o ther s ta te of af fa i rs , the l ine i s ver t ica l . These two dis t inc tintensional re la t ions for a s imilar same arrangement of objects are possible because they canbe defined on a domain space, rather than a domain.

Nonethe less , Guar ino recognizes some d isadvantages wi th the use of se t s of poss ib lestates of affairs. Let us consider a particular case he mentions, albeit briefly. Suppose that wehave the same domain space and objects , but we now want to represent the s ta tes of affairsdeno ted by “ t r i ang le” and “ t r i l a t e ra l . ” Here, both cases have the same extension in allpossible worlds. Despite this, the meaning is different in each case. In the case of “triangle,”the angles are central to the definition of this plane. And in the case of “trilateral,” theemphasis is on its sides. However, this intensional distinction cannot be represented because,unlike our previous case, the spatial situatedness of the objects in each case is not displayeddifferently in the domain space. It would seem, then, that the intensional account of aconceptual izat ion cannot be uniquely represented whenever two or more s ta tes of affa i rsdisplay the same spat ia l a r rangement and s i tua tedness on the domain space . The ques t ion i s ,does this failure exemplify some problems of (human) knowledge representation - itslimits? An important consideration in this regard concerns the tools employed forrepresenta t ion. The informat ion sys tems sphere seems to re ly heavi ly on se t - theoret ica l toolsfor model ing and representa t ion purposes . But the l i te ra ture a lso presents o ther a l te rna t ives ,such as mereology, mereotopology, and category theory [9, 10 , 11 , 13 , 16 , and 201. Theseconsiderations concerning the most appropriate tools for representation belong, however, to aseparate investigation.

Instead, we shall consider how Guarino uses sets of possible states of affairs to refinethe def in i t ion of ‘conceptua l iza t ion . ’ He wr i tes , “a conceptua l iza t ion i s a se t of conceptua lrelations defined on a domain space” [4]. We shall recall that Guarino calls intensionalrelations also conceptual relations, and their emphasis is on meaning. The conceptualization,then, as a set of conceptual relations, contains an account of meaning for all possible relationsbetween the objects in the domain space . Such an account of meaning would involve theformulat ion of the assumptions concerning al l the possible s ta tes of affairs of the domainspace, as well as the formulation of the definitions for the meaning of each relation of objectscorresponding to each poss ib le s ta te of a f fa i rs . Guar ino sugges ts tha t the def in i t ion of thein tens ions or meanings can be represented as funct ions , and the idea i s to def ine a se t offunctions that includes all possible functions in every possible world.

To comple te the p ic ture tha t Guar ino presents , le t us now turn our a t t en t ion to there la t ion between a conceptual iza t ion and an IS ontology. Presumably , the ro le making theaxiomatic theory explicit falls squarely on the IS ontology. However, an IS ontology may notadhere per fec t ly to a par t icu lar conceptual iza t ion due to d i f f icul t ies in representa t ion tha t i tmay encounter . We have examined one such diff icul ty earl ier ; namely, the t r iangle andtrilateral case. Nonetheless, at least in principle, an IS ontology is constrained by itsontological commitment to a particular conceptualization. Additionally, Guarino stresses thatan IS onto logy i s l anguage-dependent . Accord ingly , an IS onto logy must conform to apart icular formal language.

In th i s l igh t , l e t us to recons ider Guar ino’s def in i t ion of an IS on to logy: a log ica ltheory account ing for the intended meaning of a formal vocabulary. This def ini t ion clear lyidentifies the IS-type ontology with logical theory. It also adds the dimension of meaning thatwas not present in Gruber’s definition. Similarly to Gruber’s definition, however, Guarino’sdefinition may not be perspicuous to an interdisciplinary audience. We shall attempt to restatei t in more s imple language , but a l so to incorpora te the ins ight tha t we have drawn f romGruber . One decis ion to make is between the terms ‘ logical theory’ or ‘ formal iza t ion. ’ Theformer may be equivocated with the pr inciples of deduct ive reasoning, and the la t ter may betoo vague. In this case, then, perhaps a different term would be best . I t may be that the term‘axiomatic theory’ is the most adequate and widely accepted. The rest of the reformulation is

193

a matter of combining the best of both definitions, and I shall produce this at the end, after weconsider one last point.

4. The Fundamental Differences Between Information SystemsOntology and Philosophical Ontology

This b r ings the d i scuss ion to the sub jec t o f the unders tand ing o f ph i losophy andontology, as a branch of phi losophy, on the par t of the informat ion systems community . Wehave ear l ie r accepted Gruber’s rough charac ter iza t ion of phi losophica l onto logy, so we neednot review it again. When Guarino speaks of the philosophical sense of ontology, he says thatit is “a particular system of categories accounting for a certain vision of the world” [4]. “Assuch,” he adds , “ th is sys tem does not depend on a par t icu lar language .” We can accept th isrough characterization if we agree that the expression ‘vision of the world’ is a mere,fucon depar ler . In o ther words , the meaning of th is express ion i s not l i te ra l ; a f o r t i o r i , i t doe s no timport the notion of relativity into the definition such that it presupposes that the vision ofworld is always relative to the agent. Instead, we shall assume that it is a loose way to refer tothe slice of reality under investigation.

After considering Gruber’s and Guarino’s definition of IS ontology and theirrespec t ive s ta tements about phi losophica l onto logy, two th ings a re c lear . F i rs t , the meaningof the term ‘ontology’ in information systems circles is distinct from its originalphilosophical meaning. Second, the first observation is generally known in IS circles.Regardless, this meaning disparity can cause great confusion in interdisciplinary discussions.A so lu t ion tha t Guar ino sugges t s i s a s fo l lows . On the one hand , we have h i s de f in i t ion o fphilosophical ontology: a particular system of categories accounting for a slice of reality. Onthe o ther hand, we have h is def in i t ion of IS onto logy: a logica l theory account ing for theintended meaning of a formal vocabulary. Guarino recognizes that these two senses of‘ontology’ are different; however, he also believes they are related to each other. “In order tosolve the terminological impasse,” he says, “we need to choose one of them, inventing a newname for the other.” More specifically, his solution is that the term ‘ontology’ remain as thename for the IS-type ontology, and the term ‘conceptualization’ be used to refer tophi losophica l on to logy . This so lu t ion may poss ib ly work wi th in the informat ion sys temssphere, but it will not help to alleviate the language confusions interdisciplinarily. But, moreimportantly, if we set aside names and focus only on meanings, what Guarino calls aconcep tua l i za t ion i s no t wha t ph i lo soph ica l on to logy i s . Pe rhaps ph i lo soph ica l on to logy i snot as well understood as it may appear.

Prima fac ie , some of the def in i t ions for the term ‘conceptual iza t ion’ s t r ike a c loseresemblance to the nature of a material (i.e., non-formal) philosophical ontology. Forexample , Gruber expla ins tha t in theory a conceptua l iza t ion i s cons t i tu ted by the objec ts insome area of interest , and the relat ions among them [5]. An on to log i ca l i nves t i ga t i on o f aphi losophical and mater ia l ( i .e . , non-formal) nature aims to descr ibe the s t ructure of thedomain of objects being examined, including the objects there in and the re la t ions amongthem. The inference that ‘conceptualization’ and ‘material philosophical ontology’ areidentical would be possible if it were not for the following. Gruber explains that, in apract ica l sense , a conceptual iza t ion i s “an abs t rac t , s impl i f ied v iew of the wor ld” [5]. Wehave a l ready observed tha t such a conceptua l iza t ion i s a t leas t one leve l of explanat ionremoved f rom the descr ip t ive level of explanat ion where phi losophical ontology res ides . Inother words, Gruber’s practical definition of ‘conceptualization’ cannot be construed as alsoreferring to philosophical ontology.

Now let us consider Guarino’s definition of ‘conceptualization’ once again. For him, a‘conceptualization’ is a set of conceptual relations defined on a domain space [4]. Thesoph i s t i ca t i on unde r ly ing wha t Gua r ino so succ inc t ly p re sen t s i n t h i s way add res se s afundamenta l cons idera t ion in the inves t iga t ions of ph i losophica l on to logy . Suppose , forexample, that the ontologist is occupied with the domain of economic objects. He will presentthe objects of this domain, such as goods, price, money and others. But he will also advance

194

def ini t ions for each category of objects that specify the necessary and sufftcient membershipcondi t ions for each category. Meaning plays an important ro le in th is examinat ion, s ince thesame thing can have two different extensions depending on the meaning. For example, adollar bill may have two distinct extensions: one applies to the category ‘money’ (as a meansof exchange), and another applies to the category ‘good’ (as a unit of currency in the currencytrading market). In this sense, the contextual meaning would be significant.

But let us consider another case that presents two distinct expressions that apply to thesame category. For example , ‘bucks’ and ‘c lams’ are two dis t inct express ions that may applyto the ca tegory ‘money’ in a par t icular contextual meaning. In th is case , these express ionsapply nei ther to adul t male deer , nor to the shel l f i sh , respect ively . However , the contextualmeaning of these express ions is not re levant to the purposes of es tabl ishing a mater ia lontology of economic objects. The point is that the investigation is not concerned with howpeople know th ings in a par t icu la r sphere , nor about how they exper ience these th ings , o rwhat language they use to refer to them. This is the concern of epistemology, not of ontology.Epis temology, broadly const rued, i s concerned wi th knowledge and semant ics . Rather , thechief concern of phi losophica l on to logy i s to d iscover what ex is t s in any domain of objec ts ,in order to advance a def in i t ion for each ca tegory of objec ts based on the re la t ions exis t ingamong the objects. Money, for example, is the medium of exchange that agents employ toobta in consumpt ion goods . The re la t ion be tween money and goods i s cap tured by the not ionof exchange that , in turn, ident i f ies ‘exchange’ as another category of economic objects . Thedescr ip t ion of a mater ia l ontology of economic objects thus presents the s t ructure of thedomain by careful ly piecing together a l l the economic categor ies and thei r re la t ions . I t mustbe c lear that meaning is fundamental for the specif icat ion of categories and their boundaries .E.g . , money is th is , but not that , so when a d i f f icul t case ar ises , such as the presence ofcounterfe i t money, i t i s c lear that th is i s not money because fa lse money is not a k ind ofmoney but , ins tead , i t i s not money a t a l l . But an inventory of the vocabulary tha t economicagents use to refer to money is not relevant at all.

I t i s c lear , then, tha t an account of meaning tha t c lar i f ies the in tens ional re la t ionsbetween objects in a domain space is of significant currency to the formation of aconceptual iza t ion. The fundamental reason for th is i s that a conceptual iza t ion, as Guar inopoints out, deals not only with objects and the relations that hold among them, but also withvocabulary and concepts . The re levance of th is r ich not ion of ‘conceptual iza t ion’ for thedevelopment of IS ontologies is clear. However, there is no parallel with philosophicalonto logy. In some respec ts , th i s not ion of conceptua l iza t ion i s more ak in to ep is temology.Regardless of the exis tence of d i f ferences , phi losophica l ontology can s t i l l cont r ibute to theframing of a conceptualization and to the development of an IS ontology. Perhaps the greatestcontribution that philosophical ontology can offer is the discovery of certain truths about thedomain under inves t iga t ion , i t s na ture , scope , boundar ies , and d is t inc t iveness f rom a l l o thersimilar or related domains.

5. Some Suggestions for a Terminological ReconciliationThere i s no quest ion that the col laborat ion between informat ion sys tems researchers

and philosophers should continue. As a philosopher, I have attempted to make a contributiontoward a terminological c lar i f ica t ion of phi losophical ontology. This can be summed up inthree points. First, the objective of philosophical ontology is description, and its commitmentis to truth. Second, philosophical ontology is an investigation into the nature and existence ofthings in the world, and this investigation must not be entirely dependent on our knowledgeof things in the world. Third and finally, philosophical ontology aims at the objectivedescription of any domain of objects. This is not meant to deny that the investigation is, or atleast should be, grounded in the world with which we have our cognitive encounters.Nonetheless , one of the th ings we have learned f rom these cogni t ive encounters i s tha tsometimes we are right, and sometimes we are in error. To complicate matters further, weknow that we do not always know when we are right or when we are in error. A theory about

195

what ex is t s in th is or tha t domain of objec ts would be of l i t t l e serv ice i f the theory had nobasis upon which to warrant its plausibility, or from which to defend it from other competingtheor ies . Consequent ly , the bel iefs upon which our concepts are founded must be tes tedwithin the context of a particular real-world instance of an object in the domain underinvest igat ion. This dis t i l la t ion of t rue bel iefs f rom false bel iefs is a necessary par t of thedifficult task of achieving a more objective description.

To conclude, I shall propose two definitions, one for each of the two key terms of ourforegoing discussion. The purpose for this is to put forth a unified definition that isinterdisciplinarily understandable. The first concerns the definition of an IS ontology.

An IS ontology is an axiomatic theory made explicit by means of aspecif ic formal language. The IS ontology is designed for a t least onespec i f ic and prac t ica l appl ica t ion . Consequent ly , i t depic ts the s t ruc tureof a specif ic domain of objects , and i t accounts for the intended meaningof a formal vocabulary or protocols that are employed by the agents ofthe domain under investigation.

The second concerns the definition of a conceptualization.

A conceptualization is the universe of discourse at work in every possiblestate of affairs for the particular domain (or domain space) of objects thatis targetted by the IS ontology.

It is my hope that these proposed revisions spark further refinement and clarification.

6. AcknowledgementsI am grateful as ever to Barry Smith for his generosity with his time and insights. I

would also like to thank the three anonymous reviewers, as well as my colleagues, KevinSchmiesing and Stephen Grabill, for their comments. Not least of all, I am indebted to DaveCooper, Information Systems Manager at The Acton Institute, for his invaluable technicalassistance.

References[l] Ashenhurst, R.L. Ontological Aspects of Information Modeling. Minds and Machines, 6

(1996) 287-394.

[2] Dahlgren, K. A L ingu i s t i c Onto logy . Int . J . Human-Computer Studies, 43 (1995), 890-818.

[3] Guarino, N. Formal Ontology, Conceptual Analysis and Knowledge Representation. Int.J. Human-Computer Studies, 43 (1995), 625-640.

[4] Guarino, N. Formal Ontology and Information Systems. Formal Ontology inInformation Systems. 10s P res s , 1998 .

[5] Gruber, T. R. Toward Principles,for the Design of Ontologies Usedfor KnowledgeShar ing . Int . J . Human-Computer Studies, 43 (1995) 907-928.

[6] Gruber, T. R. What is an Ontology? http:l/www.ksl.stanford.edulkstlwhat-is-an-ontology.html

[7] Hobbs, J. R. Sketch qf an Ontology Underlying the Way We Talk About the World. Int. J.Human-Computer Studies, 43 (1995) 8 19-830.

[8] Husserl, E. Logical Investigations. Routledge, 1970.

[q] La Palme Reyes, M., Macnamara, J., Reyes, G. E., and Zolfaghari, H. Count Nouns ,Mass Nouns, and Their Transformations: A UniJied Category-Theoretic Semantics.

196

Language, Logic, and Concepts: Essays in Memory of John Macnamara, The MITPress, 1999.

[lo] Lawvere, F. W., and Schanuel, S. H. Conceptual Mathematics, A First Introduction toCategories. Cambridge University Press, 1997.

[ 1 l] Magnan, F. and Reyes, G. E. Category Theo y as a Conceptual Tool in the Study ojCognition. The Logical Foundations of Cognition, Oxford University Press, 1994.

[ 121 Peregrin, J. Formalization of Language as a Means of Philosophical Analysis.Analyomen 1, Proceedings of the 1 St Conference “Perspectives in AnalyticalPhilosophy.” Walter de Gruyter, 1994.

[ 131 Poli, R. Bimodality of Formal Ontology and Mereology. Int. J. Human-ComputerStudies, 43 (1995), 687-696.

[ 141 Quine, W. V. 0. Set Theo y and Its Logic. The Belknap Press of Harvard UniversityPress, 1969.

[ 151 Reicher, M. E. Works and Realizations. Formal Ontology in Information Systems. IOSPress, 1998.

[ 161 Smith, B. Basic Concepts of Formal Ontology. Formal Ontology in InformationSystems. 10s P res s , 1998 .

[ 171 Smith B. Ontology and Information Systems.http:llwings.buffalo.edu/philosophy/facultylsmit~a~icleslontologies.htm

[ 181 Smith, B., and Mulligan, K. Frameworkfor Formal Ontology. Topoi, 2 (1983), 73-85.

[ 191 Sowa, J. F. Top-level Ontological Categories. Int. J. Human-Computer Studies, 43(1995) 669-685.

[Xl] Varzi, A. C. Bas ic Problems o f Mereotopology. Formal Ontology in InformationSystems. 10s P res s , 1998 .

[21] Ztiiliga, G. An Ontoloa o f Economic Objects . The American Journal of Economics andSoc io logy , 58 (1999) 299-312.

197