Planet Moons
Mercury
Venus
Earth
Mars
Jupiter
….
Luna
Phobos,Deimos
Io,Europa,Ganymede,Callisto,Amalthea,Himalia,Elara,Pasiphae,Sinope,Lysithea,Carme,Ananke,
Leda,Thebe,Adrastea,Metis,Callirrhoe,Themisto,Megaclite,Taygete,Chaldene,Harpalyke,Kalyke,
Iocaste,Erinome,Isonome,Praxidike,Autonoe,Thyone,Hermippe,Aitne,Eurodome,Euanthe,Euporie,
Orthosie,Sponde,Kale,Pasithee,Hegemone,Mneme,Aoede,Theixinoe,Arche,Kallichore,Helike,Carpo,
Eukelade,Cyllene,Kore,Herse
…
2, constraints are applied to existential relationships to ensure identification, in this case allowing
definitedescriptionssuchas“the Planet named ‘Mercury’”asidentifyingtermsforentities.Similarly,we
mayverbalizetheentry“Luna”intheMoonscolumnastheexistentialfactThereexistsaMoonnamed‘Luna’.
Table1.1Asamplereportextractaboutoursolarsystemplanetsandtheirmoons
Wemayverbalizetheplacingof“Earth”and“Luna”intheircolumnsonthesamerowofthetable
astheelementaryfactThePlanetnamed‘Earth’isorbitedbytheMoonnamed‘Luna’,orequivalently,TheMoonnamed
‘Luna’orbits thePlanetnamed‘Earth’.Allofthedatainthetableverbalizeasinstancesofoneofthesethree
kindsoffact.
Using ORM’s graphical notation, we may display a conceptual schema diagram for the three
atomicfacttypes,includingrelevantconstraints,asshowninFigure1.7.TheentitytypesMoonand
Planetaredepictedasnamed,softrectangles(roundedcorners).Amoonorplanetisidentifiedbyits
relationshiptoasinglevalue(inthiscaseitsname).Eachsuchrelationshipisanexampleofasimple
referencescheme,involvingasingleexistentialfacttype.Themode(manner)inwhichasinglevalue
referstoasingleentityiscalledareferencemode.Forcompactness,simplereferenceschemesmay
bedisplayedinabbreviatedformbylistingthereferencemodeinparenthesesbelowtheentitytype
name, as in Figure1.7(a). For example, Moon(.Name) uses the reference mode .Name to abbreviate an
explicit existentialfacttype(also calleda referencetype)withforward reading“Moon has MoonName”
andinversereading“MoonNameisofMoon”thatisconstrainedtobeidentifying(seelater),asshownin
Figure1.7(b). The value types MoonName and PlanetName are depicted as named, soft rectangles
withdashedlineborders.
Figure1.7AnORMschemadiag ramin(a)compactform,and(b)expandedform
Facttyperolesaredepictedasroleboxes,connectedbyalinesegmenttotheobjecttypethathosts
therole.Apredicateisdepictedasanorderedsetofroleboxes,withapredicatereadingbesideit.The
binary fact type displayed explicitly in Figure 1.7(a) has forward and inverse predicate readings,
“orbits”and“isorbitedby”,separatedbyaslash“/”.Readfromlefttoright,weobtainthefacttype
reading“MoonorbitsPlanet”.Readfromrighttoleft,wehavethefacttypereading“PlanetisorbitedbyMoon”.
The large violet dot in Figure 1.7(a) on the role connector to Moon depicts a mandatory role