Presentation on theme: "Ivan Marsic Rutgers University LECTURE 11: Specifying Systems – State Diag’s & OCL."— Presentation transcript:
Ivan Marsic Rutgers University LECTURE 11: Specifying Systems – State Diag’s & OCL
2 Topics UML State Machine Diagrams –State Activities: Entry, Do, and Exit Activities –Composite States and Nested States –Concurrency UML Object Constraint Language (OCL) –OCL Syntax –OCL Constraints and Contracts
3 State Machine Diagram: Basic Notation Delisted Listing planned Traded initial-listing tradebankruptcy, merger, acquisition, … States of Stock_i initial state indicated by terminal state indicated by event transition
4 UML Diagrams Differ from FSMs Modularization of states Concurrent behaviors
5 States of Stock_i trade Buy Sell Hold Traded Buy Sell Hold Listing planned Delisted Listing planned Traded initial-listing tradebankruptcy, merger, acquisition, … composite state
6 States of Stock_i Delisted IPO planned Traded initial-listing trade bankruptcy, acquisition, merger, … Traded IPO planned Delisted trade Buy Sell Hold initial- listing bankruptcy, acquisition, merger, … IPO = initial public offering composite state nested state
7 State Activities: Entry, Do, and Exit Activities matched archive cancel, reject view trade ExecutedArchived Cancelled submit data entry InPreparation Pending do: check_price+supply [buy] check_price+demand [sell] States of a Trading Order “do” state activity
8 timer-expired / signal-reset, set numOfAttemps := 0 User leaves without succeeding or blocking autoLockInterval -expired / Auto-locking feature not shown! State Diagram for Controller [ Recall Section 2.7.4: Test Coverage and Code Coverage ] invalid-key [numOfAttemps maxNumOfAttempts] / signal-failure invalid-key / signal-failure invalid-key [numOfAttemps maxNumOfAttempts] / sound-alarm Blocked Locked Accepting valid-key / signal-success valid-key / signal-success, set numOfAttemps := 0 Unlocked Note how the object responds differently to the same event (invalid-key in Accepting state), depending on which events preceded it
9 invalid-key [numOfAttemps maxNumOfAttempts] / signal-failure invalid-key / signal-failure invalid-key [numOfAttemps maxNumOfAttempts] / sound-alarm autoLockInterval -expired / timer-expired / signal-reset, set numOfAttemps := 0 Blocked Locked Accepting entry: start timer do: countdown valid-key / signal-success valid-key / signal-success Unlocked entry: start timer do: countdown State Diagram for Controller Need “entry” and “do” state activities for countdown timers
10 Problem: States of a Hotel Room make-reservation / arrive / depart / Vacant Occupied Reserved Problem: - but a guest may be occupying the room while it is reserved by a future guest!? - or the room may be vacant while reserved by a future guest!? need a notion of time (“timing diagram”)
11 Problem: States of a Hotel Room Vacant Reserved Time [days] Occupied Reserved by guest B C make-reservation C arrive C depart Reserved by guest C A arrive A depart B make-reservation B arrive B depart States
12 Problem: States of a Hotel Room Vacant Reserved Time [days] Occupied Reserved by guest B C make-reservation C arrive C depart Reserved by guest C A arrive A depart B make-reservation B arrive B depart What state? What if the guest is late? – “Holding” state? What if the room is overbooked? What when it is being cleaned? Issue: state transitions are weird—”Reserved” is a future state but transitioned to by a current event!
13 Object: Reservation table Object: Room occupancy Problem: States of a Hotel Room Vacant Reserved Time [days] Occupied Reserved by guest B C make-reservation Reserved by guest C A arrive A depart B make-reservation Available current time SOLUTION: Introduce a new object! reserve free Objects send messages that change states
14 Problem: States of a Hotel Room Vacant Reserved Time [days] Occupied C arrive C depart A arrive A depart B arrive B depart Available current time Object 2: Reservation table Object 1: Room occupancy We need two objects: One tracks room’s current state (occupancy) and the other its future state (reservation)
15 OCL: Object Constraint Language OCL is used in UML diagrams to –write constraints in class diagrams –guard conditions in state and activity diagrams based on Boolean logic Boolean expressions (“OCL constraints”) used to state facts about elements of UML diagrams The implementation must ensure that the constraints always hold true
17 OCL: Types of Navigation Class_A – attribute1 – attribute2 – … (a) Local attribute (b) Directly related class (c) Indirectly related class Class_A Class_B * * assocBA assocAB Class_A Class_B * * Class_C * * assocBA assocAB assocCB assocBC Within Class_A: self.attribute2 Within Class_A: self.assocAB Within Class_A: self.assocAB.assocBC
18 Accessing Collections in OCL 18 OCL NotationMeaning E XAMPLE OPERATIONS ON ALL OCL COLLECTIONS c->size() Returns the number of elements in the collection c. c->isEmpty() Returns true if c has no elements, false otherwise. c1->includesAll(c2) Returns true if every element of c2 is found in c1. c1->excludesAll(c2) Returns true if no element of c2 is found in c1. c->forAll(var | expr) Returns true if the Boolean expression expr true for all elements in c. As an element is being evaluated, it is bound to the variable var, which can be used in expr. This implements universal quantification . c->forAll(var1, var2 | expr) Same as above, except that expr is evaluated for every possible pair of elements from c, including the cases where the pair consists of the same element. c->exists(var | expr) Returns true if there exists at least one element in c for which expr is true. This implements existential quantification . c->isUnique(var | expr) Returns true if expr evaluates to a different value when applied to every element of c. c->select(expr) Returns a collection that contains only the elements of c for which expr is true. E XAMPLE OPERATIONS SPECIFIC TO OCL SETS s1->intersection(s2) Returns the set of the elements found in s1 and also in s2. s1->union(s2) Returns the set of the elements found either s1 or s2. s->excluding(x) Returns the set s without object x. E XAMPLE OPERATION SPECIFIC TO OCL SEQUENCES seq->first() Returns the object that is the first element in the sequence seq.
19 OCL Constraints and Contracts A contract specifies constraints on the class state that must be valid always or at certain times, such as before or after an operation is invoked Three types of constraints in OCL: invariants, preconditions, and postconditions An invariant must always evaluate to true for all instance objects of a class, regardless of what operation is invoked and in what order applies to a class attribute A precondition is a predicate that is checked before an operation is executed applies to a specific operation; used to validate input parameters A postcondition is a predicate that must be true after an operation is executed also applies to a specific operation; describes how the object’s state was changed by an operation
20 Example Constraints (1) Invariant: the maximum allowed number of failed attempts at disarming the lock must be a positive integer –context Controller inv: self.getMaxNumOfAttempts() > 0 Precondition: to execute enterKey() the number of failed attempts must be less than the maximum allowed number –context Controller::enterKey(k : Key) : boolean pre: self.getNumOfAttempts() self.getMaxNumOfAttempts()
21 Example Constraints (2) The postconditions for enterKey() are –(Poc1) a failed attempt is recorded –(Poc2) if the number of failed attempts reached the maximum allowed, the system blocks and the alarm bell blurts –Reformulate (Poc1) to: (Poc1) if the key is not element of the set of valid keys, then the counter of failed attempts after exiting from enterKey() must be by one greater than before entering enterKey() context Controller::enterKey(k : Key) : Boolean -- postcondition (Poc1): post: let allValidKeys : Set = self.checker.validKeys() if allValidKeys.exists(vk | k = vk) then getNumOfAttempts() = else getNumOfAttempts() = postcondition (Poc2): post: getNumOfAttempts() >= getMaxNumOfAttempts() implies self.isBlocked() and self.alarmCtrl.isOn()
22 xUnit / JUnit assert_*_() Verification is usually done using the assert_*_() methods that define the expected state and raise errors if the actual state differs Examples: –assertTrue(4 == (2 * 2)); –assertEquals(expected, actual); –assertNull(Object object); –etc.
23 TLA+ Specification [closed, unlit][open, lit] [closed, lit] turnLightOff (?) unlock(valid key) lock lock, unlock(invalid key) lock, unlock(invalid key) MAIN CONFUSION: What is this state diagram representing? The state of _what_ object?