idef3_kbsi_report (1013870), страница 41
Текст из файла (страница 41)
This can be captured in situationtheory by counting temporal intervals as individuals, and including a temporal parameterexplicitly among the arguments of first-order relations whenever appropriate. Thus, for instance,the property asleep will be conceived in fact to be a 2-place relation that holds betweenindividuals and temporal intervals. Thus, if s is a typical morning situation between 6:00 a.m.and 8:00 a.m.
at an individual b’s house, it is likely the case both that (supports s (asleep b 0600+)) and that (supports s (asleep b 0800 -)). (If the relevant temporal parameter is understood,then, of course, it can be suppressed as a matter of convenience.) It is presupposed in thesemantics of the version of situation theory used with IDEF3 that all subintervals of the intervalover which a situation occurs are present in the situation. So, a situation occurring from 6:00a.m. to 8:00 a.m.
supports all relevant temporal information, for example, that the interval from6:00 to 6:15 precedes the interval from 6:30 to 6:45.A.4.2Types, UOBs, and ProcessesIn most physical systems, one observes multiple occurrences of situations that are similar insome respect. In such cases, the similar situations are said to be of the same type. For instance, asituation in which Bill Clinton is running on Tuesday and another in which he is running onWednesday, though perhaps different in many respects, are similar insofar as Clinton is runningin them, and are therefore instances of the same type of situation. Situation types are thusgeneral, repeatable patterns that can be exhibited by many difference specific situations. This,however, is precisely the character of a UOB in IDEF3, and UOBs are therefore identified withsituation types.
A situation type is specified in situation theory by an operator that abstracts oversimilar situations and an appropriate abstraction variable;17 here we will use the operator “typeof”. Thus, the activity just noted is represented as “(type-of ?sit (supports ?sit (runningClinton)))”. Similarly, distinct objects can be the same in certain respects, and can be thought ofas instances of the same object type.
Thus, Bill Clinton and Jimmy Carter are alike insofar asthey are male politicians; i.e., they are both of the type male politician. Thus, male politician canbe thought of as a property shared by Clinton and Carter, and can be denoted in the elaborationlanguage by “(type-of ?x (and (politician ?x) (male ?x)))”. In IDEF3, both situation types andobject types can simply be identified with properties—of situations and individuals, respectively.17In situation theory proper, variables correspond semantically to actual “variable objects” in the world, knownsometimes as “parameters” or “indeterminates.” For purposes here these entities can be avoided, though theremay be certain representational needs that require them.207The operator “type-of” can be understood to be simply a notational variant of the propertyabstraction operator “kappa” (see Section A.1.3 above).The importance of types in the context of process capture and process modeling—and,indeed, in the context of modeling generally—is that the semantic content of most all processdescriptions concerns types.
More exactly, a typical process is best thought of as a structuredcollection of UOBs related to one another in a manner that reflects the process flow in a givenactivation of the process; i.e., the temporal relations between the instances of those types in anactivation. For instance, consider the painting process depicted in Figure A-1. This diagramdepicts a general process that must begin with an instance of the UOB Paint Part (represented bythe Paint Part box with no predecessor), followed by an instance of Test Coverage.
At thatpoint, depending on the outcome of the test, an instance of the process can either loop back toanother instance of Paint Part, or continue on to have the part dried. Thus, there are, inprinciple, infinite ways this single process can be instantiated by particular courses of events,depending on how many times such a course of events loops back to repeat the Paint Partactivity.PaintPart1XPaintPartTestCoverage3Dry PartX42Figure A-1Paint/Review/Dry ScenarioMore generally, a situation type—i.e., a UOB—is specified in terms of a variable “?sit”ranging over arbitrary situations and a formula j specifying the conditions common to situationsof that type.
Specifically, an activity is referred to by terms of the form “(type-of ?sit j)”, read“the type of situation such that j”. Thus, recalling the example above, “(type-of ?sit (supports?sit (running Clinton)))” is read “the type of situation such that it supports Clinton running,” or alittle more naturally in this case, “the type of situation in which Clinton is running.” A situation sis of type T = (type-of ?sit j) just in case j is true when “?sit” refers to s.
If j is of the form“(supports ?sit i)”, where i is an infon term, the activity is said to be specified internally;otherwise it is specified externally. The difference is that an internal specification describes theactivity in terms of the infons that its occurrences support, whereas an external specification mayrefer instead to properties of the activity beyond the infons that its occurrences support, such as,e.g., the causes of its occurrences or the costs involved in maintaining them.208A.4.3Basic Situation Theoretic RelationsSituation theory is highly typed in the sense that the world it describes is partitioned into anumber of different semantic categories; most notably, objects, first-order properties andrelations, infons, situations, courses-of-events, object types, situation types, processes, andtemporal intervals.
To capture these distinctions, the theory of situations developed within theelaboration language defines terms that denote each of these categories. In addition, a variety ofterms are defined that signify a class of special relations, along with axioms that expressprecisely what categories of objects can stand in these relations. With these terms at his or herdisposal, a user is able to clearly express any additional information or constraints not expressiblein terms of the IDEF3 schematic language.Specifically, then, the supports and denies relations between situations and infons werediscussed at length above. The occurrence-of relation holds between a situation s and a UOB Ujust in case s is an instance of U. The activation-of relation holds between a course-of-events cand the process P just in case c is an activation of P.
The occurs-in relation holds between asituation s and courses-of-events c just in case s occurs in c. The activity-in relation mirrors thisrelation at the type level—it holds between a UOB U and a process P just in case U is among thesituation types that constitute P. The of-type relation holds between a situation s and a UOB Ujust in case s is an instance of U.
The object-in relation holds between an object b and either asituation s or a UOB U just in case b occurs in s or in instances of U.A variety of temporal relations are needed to describe the temporal structure of complexprocesses. The only primitive relation required is meets, where, intuitively, one interval i meetsanother j just in case the endpoint of i is the starting point of j. Further relations—e.g., precedes,starts, finishes, overlaps, during—can be defined in terms of meet, as illustrated in Section A.5.4below. Note that intervals are treated as first-order objects, thus the temporal relations are allfirst-order relations.
Temporal relations are used to define a variety of corresponding temporalrelations among situations.A.5A Formal Language for IDEF3 ElaborationsIn this section the core elaboration language is extended with definitions that introduce thebasic semantic categories of situation theory along with appropriate defining axioms. To aidcomprehension, axioms are usually first given in English, and are formatted in italics to enhancereadability. Note that this extension of the elaboration language core is not a formalization offull blown situation theory. Rather, it is a specification of the basic constructs needed to expresssituation-based IDEF3 elaborations, as illustrated in the examples above and in Section 3,“IDEF3 Process Description Language,” of this report.
Note also that no formal model theory isprovided here. Since the purpose of this report is to enable enterprise modelers and knowledgeengineers to effectively use IDEF3, informal, intuitive characterizations of the semantics of thelanguage have been provided instead.209A.5.1Extending the Core Elaboration LanguageThe first task to be addressed is to extend the core elaboration language to the full IDEF3elaboration language, including a new class of infon terms. This is accomplished by adding thefollowing clause:<infonterm> ::= (<term> <term>+) |(and <infonterm> <infonterm>+) |(or <infonterm> <infonterm>+) |(<quant> <var> <infonterm>)Infon terms of the form (<term> <term>+) are known as atomic infon terms.In addition, the category <compterm> is modified to include the category <infonterm>.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
