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Modelling relationships Peter Gorm Larsen TIVDM1 Modelling relationships 1 Agenda Mapping Characteristics and Primitives • The MSAW Example Revisited • The Congestion Warning System Revisited TIVDM1 Modelling relationships 2 Mapping Characteristics • Mappings are unordered collections of pairs of elements (a maplet) with a unique relationship • There can be many copies of each maplet • The elements themselves can be arbitrary complex, e.g. they can be mappings as well • Mappings in VDM++ are finite • Mapping types in VDM++ are written as: • map Type1 to Type2 • inmap Type1 to Type2 (for injective mappings) TIVDM1 Modelling relationships 3 Mapping Enumeration • A maplet is written with curly brackets: “{ domv |-> rngv}” • A mapping enumeration consists of a comma-separated list of maplets enclosed between curly brackets, ”{…}” • For example • {1 |-> 5,8 |->1,3|-> 9} • {true|->1, false|->0,false|->0} • {“Peter”|->{}, “Frodo”|->{4,3},”John”|->{2,4}} • {‘g’|->1,’o’|->0,’d’|->1} • {3.567|->3, 0.33455|->0,7|->7,7|->,7|->7,7|->7} Are all mappings • The empty mapping can be written as “{ |-> }” TIVDM1 Modelling relationships 4 Mapping Domain • The domain of a mapping is the collection of the first elements in the maplets of a mapping • Multiple occurrences of the same value does not count • The domain of a mapping M is written as “ dom M” • Quick examples: • dom {“Peter”|->1,”Nico”|->2,”Paul”|->3} • dom { |-> } • dom {3|->2,3|->2,1|->8} TIVDM1 Modelling relationships 5 Mapping Range • The range of a mapping is the collection of the second elements in the maplets of a mapping • Multiple occurrences of the same value does not count • The range of a mapping M is written as “rng M” • Quick examples: • rng {“Peter”|->1,”Nico”|->2,”Paul”|->3} • rng { |-> } • rng {3|->2,3|->2,1|->8} TIVDM1 Modelling relationships 6 Mapping Equality • Two mappings are equal if • both have the same domain and • for all elements in the domain the corresponding range values are equal • Quick examples: • {2|->4,1|->2} = {1|->2,2|->4} • {true|->1, true|->1, false|->0} = {false|->1, true|->1} • {1|->3,3|->8,8|->1} = {8|->3,3|->1,1|->8} • {1|->{3,4,5},2|->{4}} = {3|->{3,5,4},2|->{4,4,4}} TIVDM1 Modelling relationships 7 Mapping Application • Looking up in a mapping for a given domain value yields the corresponding range value • Mapping application is written as function application, i.e. mapping(domain expression) • Quick examples: • {1|->2,3|->4,5|->6}(3) • {true|->1,false|->2,}(true) • {[5]|->1,[6,1]|->2,[4,4,4]|->3}([6,1]) • {5|->[5],6|->[6,1],4|->[4,4,4]}(6) TIVDM1 Modelling relationships 8 Mapping Domain Restrictions • It is possible to restrict the domain of a mapping to or by a given set of elements • Domain restrictions are written as: • s <: m (restricting domain to the set s) • s <-: m (restricting domain by the set s) • Quick examples: • {1,2,2} <: {1 |->5,4|->2} • {3,4} <: {1|->7,2|->4} • {1,3} <-: {3|->8,5|->1} • {2,4} <-: {8|->4,3|->6} TIVDM1 Modelling relationships 9 Mapping Range Restrictions • It is possible to restrict the range of a mapping to or by a given set of elements • Range restrictions are written as: • m :> s (restricting range to the set s) • m :-> s (restricting range by the set s) • Quick examples: • {1 |->5,4|->2} :> {1,2,2} • {1|->7,2|->4} :> {3,4} • {3|->8,5|->1} :-> {1,3} • {8|->4,3|->6} :-> {6,4} TIVDM1 Modelling relationships 10 Mapping Override and Merge • It is possible to combine two mappings by either merging them together (similar to set union) or by letting one mapping override another mapping • Merging is written with munion using infix notation • munion requires mappings to be conformant, i.e. if domains have common elements they map to the same range value • Overriding is written with ++ using infix notation and the mapping from the second argument overrides the maplets from the first argument • Quick examples: • {1|->2,3|->4} munion {2|->3,4|->1} • {5|->7,8|->0} munion {6|->3,5|->7} • {1|->2,3|->4,2|->8} ++ {2|->3,4|->1} • {5|->7,8|->0,6|->9} ++ {6|->3,5|->9} TIVDM1 Modelling relationships 11 Distributed Mapping Merge • Given a set of mappings it is possible to take a distributed merge if all the mappings are conformant • Distributed mapping merge is written as “merge ms” where ms is a set of mappings • Quick examples • merge {{2|->4},{3|->4,1|->2},{2|->4,7|->3}} • merge {{5|->”me”,7|->”too”},{6|->”what”,8|->”now”}} • merge {} TIVDM1 Modelling relationships 12 Mapping Inverse • A mapping is injective if all its domain elements map to different range elements • For injective mappings it is possible to construct the inverse mapping (swapping domain and range elements) • This is written as “inverse m” using prefix notation • Quick examples: • inverse {1|->2,3|->4,2|->3,4|->1} • inverse {5|->7,8|->0,6|->3,5|->7} • inverse {1|->2,3|->4,2|->8,6|->3,4|->1} • inverse {|->} TIVDM1 Modelling relationships 13 Map Operators dom m Domain (map A to B) -> set of A rng m Range (map A to B) -> set of B m1 munion m2 Merge (map A to B) * (map A to B) -> (map A to B) m1 ++ m2 Override (map A to B) * (map A to B) -> (map A to B) merge ms Distr. merge set of (map A to B) -> map A to B s <: m Dom. restr. to set of A * (map A to B) -> map A to B s <-: m Dom. restr. by set of A * (map A to B) -> map A to B m :> s Rng. restr. to (map A to B) * set of A -> map A to B m :-> s Rng. restr. by (map A to B) * set of A -> map A to B m(d) Map apply (map A to B) * A -> B inverse m Map inverse inmap A to B -> inmap B to A m1 = m2 Equality (map A to B) * (map A to B) -> bool m1 <> m2 Inequality (map A to B) * (map A to B) -> bool TIVDM1 Modelling relationships 14 Mapping Comprehensions • Using predicates to define mappings implicitly • In VDM++ formulated like: • {maplet | list of bindings & predicate} • The predicate part is optional • Quick examples • {i |-> i*i | i: nat1 & i <= 4} • {i**2 |-> i/2 | i in set {1,…,5}} TIVDM1 Modelling relationships 15 Questions • What are the mapping enumerations for: • {x |-> x|x in set {8,…,1} & x < 3} • {x |-> 2*x|x in set {1,…,10} & x > 3 and x < 6} • {{y} |-> y - 8| y in set {3,1,7,3}} • {x |-> x+6| x in set {1,2}} • {x|->mk_(x,8)| x in set {1,2,7} & x > 4} • {y|->y|y in set {0,1,2} & exists x in set {0,…,3} & x = 2 * y} • {x|->x = 7| x in set {1,…,10} & x < 6} TIVDM1 Modelling relationships 16 Agenda Mapping Characteristics and Primitives The MSAW Example Revisited • The Congestion Warning System Revisited TIVDM1 Modelling relationships 17 Making use of FO Identification • In the set version of the MSAW model we had: class AirSpace is subclass of GLOBAL instance variables airspace : set of FO := {}; inv forall x,y in set airspace & x <> y => x.getId() <> y.getId(); • If we use mappings this can be done simpler class AirSpace is subclass of GLOBAL instance variables airspace : map FOId to FO := {|->}; TIVDM1 Modelling relationships 18 An Updated Class Diagram TIVDM1 Modelling relationships 19 Adding and Removing Flying Objects class AirSpace is subclass of GLOBAL operations public addFO : FO ==> () addFO(fo) == airspace := airspace munion {fo.getId() |-> fo} pre forall x in set rng airspace & fo.getId() <> x.getId(); public removeFO : FOId ==> () removeFO(id) == airspace := {id} <-: airspace; … TIVDM1 Modelling relationships 20 Getting Hold of a FO and Airspace class AirSpace … public getFO : FOId ==> FO getFO(id) == return airspace(id) pre id in set dom airspace; public getAirspace : () ==> set of FO getAirspace() == return rng airspace; TIVDM1 Modelling relationships 21 Can Radars use Mappings? class Radar is subclass of GLOBAL instance variables location : Coordinates; range : nat1; detected : map FOId to FO; priority : seq of FO := []; operations public Scan : AirSpace ==> () Scan(as) == (detected := { x.getId() |-> x | x in set as.getAirspace() & InRange(x) }; UpdatePriorityList() ); TIVDM1 Modelling relationships 22 Removing and Adding FOs removeNotDetected : set of FO ==> () removeNotDetected(fos) == priority := [priority(i) | i in set inds priority & priority(i) in set fos]; addNewlyDetected : map FOId to FO ==> () addNewlyDetected(newlyDetect) == priority := priority ^ set2seqFO(rng newlyDetect); functions set2seqFO : set of FO -> seq of FO set2seqFO(fos) == if fos = {} then [] else let fo in set fos in [fo] ^ set2seqFO(fos\{fo}) TIVDM1 Modelling relationships 23 Updating Priority List UpdatePriorityList : () ==> () UpdatePriorityList() == let notDetect = elems priority \ rng detected, newlyDet = detected :-> elems priority in ( removeNotDetected(notDetect); addNewlyDetected(newlyDet) ); TIVDM1 Modelling relationships 24 Overview in Air Traffic Controller class Radar … public getDetectedMap : () ==> map FOId to FO getDetectedMap() == return detected; end Radar class AirTrafficeController operations OverviewAllRadars: () ==> map FOId to FO OverviewAllRadars() == merge {r.getDetectedMap() | r in set radars} end AirTrafficeController TIVDM1 Modelling relationships 25 Agenda Mapping Characteristics and Primitives The MSAW Example Revisited The Congestion Warning System Revisited TIVDM1 Modelling relationships 26 The CWS Revisited • Introducing a more realistic road network • Introducing the notion of lanes • Introducing name servers • Adding sensors and actuators gradually TIVDM1 Modelling relationships 27 The Revised CWS System TIVDM1 Modelling relationships 28 Two Injective Mappings at VDM++ Level class CWS instance variables roadNetwork: inmap Location to CongestionMonitor := {|->} sensors: inmap Location to (inmap Lane to PassageSensor) := {|->}; types public Location = nat1; public Lane = nat1 … end CWS TIVDM1 Modelling relationships 29 Class Diagram for Revised CWS TIVDM1 Modelling relationships 30 Adding a new Sensor class CWS … operations public AddSensor: Location * Lane ==> () AddSensor(loc, lane) == def passageSensor = new PassageSensor(loc, lane) in let sensorAtLane = {lane |-> passageSensor} in if loc in set dom sensors then sensors(loc) := sensors(loc) munion sensorAtLane else sensors := sensors munion {loc |-> sensorAtLane}; end CWS TIVDM1 Modelling relationships 31 Dealing with Name Servers • Control over the actuation managers • Each control manager control multiple locations class NameServer instance variables am: map ActuatorManager to (set of CWS`Location) := {|->} … end NameServer TIVDM1 Modelling relationships 32 Setting Actuation Managers in control class NameServer operations public SetActuatorManager: ActuatorManager * set of CWS`Location ==> () SetActuatorManager(actuatorManager, locations) == am := am ++ {actuatorManager |-> locations}; end NameServer TIVDM1 Modelling relationships 33 Getting an Actuation Manager class NameServer operations public GetActuatorManager: [CWS`Location] ==> [ActuatorManager] GetActuatorManager(loc) == if loc = nil then return nil else let locations = inverse am in let locationSet in set dom locations be st loc in set locationSet in return locations (locationSet); end NameServer TIVDM1 Modelling relationships 34 Message Logs inside Congestion Sensors class CongestionSensor is subclass of Sensor … instance variables passageSensors: map CWS`Lane to PassageSensor := {|->} end CongestionSensor Notice that the first box on page 180 in the book is wrong. This is the right version. TIVDM1 Modelling relationships 35 Issue Congestion Warnings class CongestionSensor is subclass of Sensor public IssueCongestionStatus: () ==> CongestionSensor`CongestionStatus IssueCongestionStatus() == def averagespeed = min ({passageSensors(lane). AverageSpeed(NoPassages) | lane in set dom passageSensors}) in if averagespeed < CongestionThreshold then return <Congestion> elseif averagespeed > NoCongestionThreshold then return <NoCongestion> else return <Doubt> end CongestionSensor TIVDM1 Modelling relationships 36 Managing Actuators class ActuationManager … instance variables as: inmap CWS`Location to Actuator := {|->}; ns: NameServer end ActuationManager TIVDM1 Modelling relationships 37 Adding Actuator at a given Location class ActuationManager … operations public AddActuator: CWS`Location ==> () AddActuator(loc) == def actuator = new Actuator() in (as := merge {as, {loc |-> actuator}}; ns.SetLocation(self, loc) ) pre loc not in set dom as; end ActuationManager TIVDM1 Modelling relationships 38 Removing Actuators class ActuationManager … operations public RemoveActuator: Actuator ==> () RemoveActuator(actuator) == as := as :-> {actuator}; end ActuationManager TIVDM1 Modelling relationships 39 Replacing Actuators class ActuationManager … operations public ReplaceActuator: Actuator * Actuator ==> () ReplaceActuator(actuator, newActuator) == as := as ++ {(inverse as)(actuator) |-> newActuator}; end ActuationManager TIVDM1 Modelling relationships 40 Showing Signal at a given Location class OperatorControl … public ShowSignal: CWS`Location * CongestionMonitor`Signal ==> () ShowSignal(location, signal) == ( def downstreamLocation = Downstream(location, ns.GetLocations()); downstreamManager = ns.GetActuatorManager(downstreamLocation); downstreamSignal = if downstreamManager <> nil then downstreamManager.GetSignal(downstreamLocation) else nil; actuator = as(location); upstreamLocation = Upstream(location, ns.GetLocations()); upstreamManager = ns.GetActuatorManager(upstreamLocation); upstreamSignal = if upstreamManager <> nil then upstreamManager.GetSignal(upstreamLocation) else nil in ( ShowSignalAtLoc(signal,downstreamLocation, downstreamSignal,actuator); ShowSignalUpstream(signal,upstreamLocation,upstreamManager,upstreamSignal) ) ) pre location in set dom as; end OperatorControl TIVDM1 Modelling relationships 41 Operator Utilities class OperatorControl … operations public WriteLog: seq1 of char * CWS`Location ==> () WriteLog(message, location) == let newMessage = message ^ int2String(location), messages = if location in set dom messageLog then messageLog(location) ^ [ newMessage ] else [ newMessage ] in messageLog := messageLog ++ {location |-> messages}; public CongestionSpots: () ==> set of CWS`Location CongestionSpots() == return dom messageLog; end OperatorControl TIVDM1 Modelling relationships 42 Summary • What have I presented today? • The notion of mappings as ordered collections • The basic operations in VDM++ for manipulating mappings • The MSAW example again • The congestion warning system example again • What do you need to do now? • Complete your project • Provide report and source model to me • Fill out evaluation form • Tell me whether you would like an exam trial session TIVDM1 Modelling relationships 43 Quote of the day Engineering is a great profession. There is the satisfaction of watching a figment of the imagination emerge through the aid of science to a plan on paper. Then it moves to realization in stone or metal or energy. Then it brings homes to men or women. Then it elevates the standard of living and adds to the comforts of life. This is the engineer's high privilege. By Herbert Hoover (1874 - 1964) TIVDM1 Modelling relationships 44

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