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Matters are more or less the same if the referent is a TSreferent. Consider the schematic in Figure 3-44, and suppose the referent refers to theschematic in Figure 3-41.OS/SCDFigure 3-44Transition Schematic with a Call-and-Continue ReferentThis schematic signifies that, in an instance of the indicated transition, there is first anobject c in state C, at which point an instance of Figure 3-41 begins, and hence someobject a begins to transition to state B through an instance of the process P; c thentransitions to state D at any point after the transition from A to B begins.
The analystdetermines exactly what it means for a transition to have begun in a given case. The mainpoints here are that (1) the series of transitions referred by a TS referent must in somesense begin before the transition from C to D completes, and (2) the transition from C toD can occur regardless of whether or not that series of transitions has completed.Additional information about the temporal sequencing of the events involved in astate transition can be added with a Call-and-Wait referent. Such a referent differsgraphically from a Call-and-Continue referent by the addition of a second vertical line tothe right of the referent name, as shown in Figure 3-45.59Referent Type/LabelLocatorFigure 3-45Call-and-Wait Referent SyntaxA Call-and-Wait referent indicates that the called situation must terminate before thenext situation in the transition can transpire.
Thus, again, with respect to Figure 3-41, aninstance p of the UOB P would have to terminate before the object in state A couldtransition to state B. Note that the end of p could coincide with the completion of thetransition in question. This is not implied in a state transition schematic with a Call-andContinue referent. Rather, the process indicated by the referent must only start before thetransition is completed; it may complete before the transition, but it could alsolegitimately continue well past the point of transition. Similarly, if the Call-and-Waitreferent in question is an TS referent, then the referenced series of transitions mustcomplete before the transition indicated in the schematic completes. Thus, if the TSreferent in Figure 3-44 was a Call-and-Wait and was again referring to the schematic inFigure 3-41, then there would have to be a complete instance of a transition from A to Bbefore an object c could complete a transition from C to D.Referents Attached to Object StatesIt is not uncommon for a given situation to “sustain” an object in a given state; arefrigeration process, for example, might sustain a given substance in a solid state.Situations of this type can be represented by the construct in Figure 3-46.UOB/PABFigure 3-46Sustaining an Object in a StateMore generally, in an occurrence of Figure 3-46, there is an instance p of the UOB Pand an object a in state A throughout the duration of p.
This requires that such an a mustexist when p begins. However, a could be in state A prior to the start of p; that is, it could60be brought into state A by some other process prior to p (the substance noted above mightactually become solid through some sort of chemical reaction), and then sustained in thatstate by p. Thus, the two instantiation patterns in Figure 3-47 are both compatible withFigure 3-46.Instance of PInstance of PAaAaBbBbFigure 3-47Instantiation Patterns for Figure 3-46Note that in the right diagram, b’s coming to be in state B prior to the end of theinstance p of P could be ruled out by changing the Call-and-Continue referent in Figure3-46 to a Call-and-Wait. In that case, only the left diagram would represent a legitimateinstantiation pattern.Object Schematics with Multiple ReferentsOften a more complex course of events than can be indicated by a single referent isinvolved in the transition from one state to another.
The details of such a course ofevents, as one would expect, can be provided by a separate process schematic. However,it is useful to be able to represent that course of events explicitly in an object schematic.For this purpose, multiple referents can be attached to a single arc.To interpret such schematics, think of the arc in a basic state transition schematic as arough time line signifying the period over which the indicated transition occurs. Thus,the position at which a referent attaches to the line in a state transition schematic Dsignifies the relative temporal order in which the indicated UOBs, scenarios, or series oftransitions begin in an instance of the transition signified by D.
So, for instance, in Figure3-48, a transition from A to B involves, first an instance p of the UOB P followed by aninstance q of Q. Since the first referent is a Call-and-Wait, p must complete before qbegins.61UOB/PBAUOB/QFigure 3-48Object Schematic with Multiple, Temporally Ordered ReferentsFigure 3-49 signifies a transition in which instances p and q of two UOBs beginsimultaneously. Note that since the first referent is once again a Call-and-Wait, p mustcomplete before the transition to B completes; since the second referent is a Call-andContinue, the same does not hold for q.UOB/PUOB/QABFigure 3-49Object Schematic with Multiple Temporally Simultaneous ReferentsFinally, Figure 3-50 illustrates the use of an additional symbol—a temporalindeterminacy marker (indicated by the small circle on the transition link)—to represent atransition in which there is (as far as is known) no definite temporal ordering to the UOBsinvolved in a transition. Instances of P, Q, and R are known to be involved in theindicated transition, but in any instance of the transition they can occur in any orderrelative to one another.62UOB/PUOB/QAUOB/RBFigure 3-50Object Schematic with Temporally Indefinite ReferentsBecause there is no definite temporal ordering between the indicated UOBs, onlyordinary (i.e., Call-and-Continue) referents are used; Call-and-Wait referents would haveno clear meaning.Complex Transition SchematicsThe processes that one might use to describe or model from an object-centered pointof view are often too complex to be captured adequately by a basic transition schematic.Hence, it is possible to build complex transition schematics, i.e., schematics with multipleobject state symbols.
Complex transition schematics correspond, roughly, to complexprocess schematics. This supports the central role of transition schematics, providingobject-centered views of processes. Hence, process schematics and transition schematicsshould be structurally similar. However, transition schematics are only a subclass of theentire class of object schematics that can be constructed in IDEF3.Consider first the complex transition schematic, illustrated in Figure 3-51.63UOB/Identify KeyConceptsUOB/ValidateConcepts4/16/1System:Milestone 1System:Milestone 2System:Milestone 3UOB/Explore KeyConcepts5/1Figure 3-51Complex Transition SchematicThe process described in this transition schematic involves a kind of system (calledsimply system) that transitions through three states: Milestone 1, Milestone 2, andMilestone 3. Because the first referent is a Call-and-Wait, in order for the system totransition from Milestone 1 to Milestone 2, the UOB Identify Key Concepts indicated bythe referent must complete.
The UOB Explore Key Concepts must then start, but becausethe referent in question is not a Call-and-Wait, it need not complete before the transitionto Milestone 2; for instance, it may be sufficient for transition that most of the identifiedkey concepts be explored. The UOB Validate Concepts must then begin after thetransition to Milestone 2 and subsequently finish before, or at least no later than, the pointat which the system has successfully transitioned to Milestone 3. Note that it is onlyrelative placement on a transition arc that is important; the distance between two pointsof attachment is irrelevant, unless that distance is zero, i.e., unless two referents areattached at the same point, which signifies that instances of the indicated events are tobegin simultaneously.As with process schematics, a transition schematic is a structural whole; it describes,in a general way, the structure of the state transitions (or, at least, a prominent set of thestate transitions) that one or more of the objects involved in a complex process undergo.Thus, a transition schematic cannot, in general, be broken into smaller pieces withoutlosing information, as a transition schematic in general depicts an entire series, ornetwork, of state transitions.
The two basic transition schematics in Figure 3-52, forinstance, do not carry as much information as the schematic in Figure 3-51.64UOB/ IdentifyKey ConceptsUOB/ValidateConcepts4/16/1System:Milestone 1System:Milestone 2System:Milestone 2UOB/Explore KeyConcepts5/1Figure 3-52Transition Schematics Not Jointly Equivalent to Figure 3-51These two schematics simply document the individual transitions from Milestone 1 toMilestone 2, and from Milestone 2 to Milestone 3.
For all these schematics,these twotransitions might never be successive in the system in any given instance. Because thereis no implication in the semantics for basic transition schematics that Milestone 1 andMilestone 2 are mutually exclusive states (regardless of whether they actually are), thesetwo figures are compatible with a situation in which there is a transition from Milestone 2to Milestone 3 before a transition from Milestone 1 to Milestone 2, as depicted in Figure3-53 (where “M1(s)” means the system is in the state Milestone 1, and so on):M1(s)M2(s)M3(s)M2(s)Figure 3-53Possible Instantiation Pattern for the Schematics in Figure 3-52Transition JunctionsTransition junctions provide a mechanism to specify the logic of potentially multiplepaths in state transition behavior. For example, Figure 3-54 illustrates the use of aninclusive disjunctive junction, indicating that an object state may transition alternativelyto one of a number of other states.65System:Milestone 3UOB/PB1B2AO•••BnFigure 3-54Disjunctive State Transition SchematicUsing a disjunctive junction that is inclusive permits a transition from A to one orpossibly more than one of the subsequent states.
To indicate exclusive disjunction, whichpermits transition to no more than one of the subsequent states, the construct in Figure 355 is used.66UOB/PB1B2AX•••BnFigure 3-55Exclusive Disjunctive State Transition SchematicBy the same token, a conjunctive schematic is introduced to indicate a transition froma given state to all of several subsequent states, as illustrated in Figure 3-56.UOB/PB1B2A&•••BnFigure 3-56Conjunctive State Transition Schematic67The semantics for schematics including logical junctions is a generalization of thesemantics for basic transition schematics. Intuitively, once again, the schematic in Figure3-56 represents a type of situation in which there is a transition involving the process P,from an object a in state A to objects a1, .
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