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OCSMP Model User practice questions

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Question 1System Behavior

In a use case diagram, which relationship inserts optional or additional behavior into a base use case at a named extension point?

  1. generalization
  2. association
  3. «extend» Correct answer.
  4. «include»

Explanation

An «extend» dependency runs from the extending use case to the base use case and identifies an extension point in the base. The added behavior happens only when the extension condition holds, so the base use case can complete without it.

Question 2System Behavior

In an activity diagram, which notation marks the initial node at which execution begins?

  1. A diamond with one incoming and several outgoing edges
  2. A solid filled circle Correct answer.
  3. A hollow circle
  4. A rectangle with rounded corners

Explanation

The initial node is drawn as a small solid filled circle and provides an outgoing control flow that starts the activity. It has no incoming edges, which distinguishes it from other control nodes.

Question 3System Behavior

A lifeline in a sequence diagram primarily represents which element?

  1. A single message exchanged between two participants
  2. The ordering rule applied inside a combined fragment
  3. A state the receiver occupies while waiting for a message
  4. One interacting participant over a period of time Correct answer.

Explanation

Each lifeline corresponds to one participant of the interaction, and its vertical extent shows that participant's existence across time. Messages are drawn between lifelines, not as lifelines themselves.

Question 4System Behavior

A state in a state machine models which concept?

  1. A condition during which an object performs an activity or waits for an event Correct answer.
  2. The atomic step in which a transition effect executes
  3. A discrete moment at which a guard condition is evaluated
  4. A signal that the object accepts asynchronously

Explanation

A state represents a situation in the life of an object in which it satisfies some condition, performs some activity, or waits for an event. Transitions move the object between states when their triggers occur and guards hold.

Question 5System Behavior

An actor appearing on a use case diagram denotes which of the following?

  1. A class that inherits from the subject
  2. A role played by a user or external element that interacts with the subject Correct answer.
  3. A use case that another use case includes
  4. An internal component that realizes the use case

Explanation

Actors describe roles external to the subject that exchange information or services with it. A single actor may be played by people, devices, or other systems, and one physical entity may play several actors.

Question 6System Behavior

How does an activity final node differ from a flow final node?

  1. It ends the entire activity and stops all remaining tokens. Correct answer.
  2. It consumes one token and lets other flows continue.
  3. It may be placed only inside an interruptible region.
  4. It is drawn as a circle containing an X.

Explanation

An activity final node terminates the whole activity, so any tokens still active elsewhere are destroyed. A flow final node merely consumes the token that reaches it, leaving other flows running.

Question 7System Behavior

On a state machine transition, what is the trigger?

  1. The guard condition that must remain true
  2. The state that the transition leaves
  3. The action executed when the transition is taken
  4. The event whose occurrence can enable the transition Correct answer.

Explanation

The trigger names the event that, when it occurs and the guard is true, allows the transition to fire. The effect is separate behavior that runs when the transition is actually taken.

Question 8System Behavior

What is the role of a decision node in an activity diagram?

  1. It synchronizes tokens arriving on several concurrent flows
  2. It duplicates each incoming token onto every outgoing edge
  3. It marks the end of a single token path
  4. It selects one outgoing edge based on guard conditions Correct answer.

Explanation

A decision node has one incoming edge and several outgoing edges, and the guards on those edges determine which single path the token takes. Guards must be mutually exclusive so that exactly one is selected.

Question 9System Behavior

A single token reaches a fork node that has three outgoing edges. How many tokens leave the fork node?

  1. No token until a matching join node is reached
  2. Two tokens, because a fork always doubles its input
  3. One token per outgoing edge Correct answer.
  4. One shared token that the downstream actions read concurrently

Explanation

A fork node copies the incoming token onto each of its outgoing edges, so the three downstream flows proceed concurrently. A join node later waits for a token on each of its incoming edges before continuing.

Question 10System Behavior

Why is an activity partition (swimlane) used on an activity diagram?

  1. To specify the events that interrupt the enclosed actions
  2. To define the parameters of the enclosing activity
  3. To show the chronological order in which actions execute
  4. To group actions by the classifier responsible for performing them Correct answer.

Explanation

Partitions group the actions of an activity according to the structural element, such as a block or organization, that owns or performs them. They support allocation of behavior to structure and do not by themselves impose sequencing.

Question 11System Behavior

What does an object flow between two actions carry?

  1. The declaration of an activity parameter
  2. The guard condition that selects a branch
  3. A control token that only enables the target action
  4. An object or data token passed from one action to another Correct answer.

Explanation

Object flows move object or data tokens, so the receiving action obtains the value or item produced by the upstream action. Control flows, by contrast, carry only control tokens that enable actions.

Question 12System Behavior

Which activity action waits for an incoming signal and consumes it before continuing?

  1. Send signal action
  2. Call behavior action
  3. Accept event action Correct answer.
  4. Value specification action

Explanation

An accept event action blocks until the specified event, such as a signal or a time event, occurs, then produces an output token. A send signal action creates and dispatches a signal instead of waiting for one.

Question 13System Behavior

A combined fragment with operator alt contains two operands, each carrying a guard. What does the fragment mean?

  1. Exactly one operand whose guard is true executes Correct answer.
  2. Both operands execute, interleaved in any order
  3. The first operand always executes and the second is optional
  4. Neither operand executes until an external event occurs

Explanation

The alt operator models alternative behaviors: the guards are evaluated and only one operand's interaction is carried out. If several guards hold, the choice among them is not determined by the notation.

Question 14System Behavior

In a sequence diagram, an open, unfilled arrowhead on a message usually indicates what?

  1. An asynchronous message for which the sender does not wait Correct answer.
  2. A message that creates a new lifeline
  3. A synchronous call for which the sender waits for a reply
  4. A reply message that returns a value

Explanation

An open arrowhead denotes an asynchronous message, so the sender continues without waiting for a response. A filled arrowhead denotes a synchronous call, whose reply is drawn as a dashed message.

Question 15System Behavior

A composite state has an entry action and contains three sequential substates. When does the composite state's entry action execute?

  1. Only when the composite state is exited
  2. Each time a transition enters any of its substates
  3. Once, when the composite state itself is entered Correct answer.
  4. Only when the composite state's final state is reached

Explanation

Entry actions of a composite state run once on entering that composite state, before the default transition into its nested content is taken. Moving among the substates afterwards does not re-execute the composite state's entry action.

Question 16System Behavior

A composite state contains two orthogonal regions. What does this imply about the object's situation?

  1. The object is in one state of each region at the same time Correct answer.
  2. The object is in exactly one of the two regions at a time
  3. The regions are alternative behaviors selected by guards
  4. Both regions must reach a final state before the state machine starts

Explanation

Orthogonal regions, separated by a dashed line, execute concurrently, so the object occupies a state in every region simultaneously. The composite state completes only when all regions have completed.

Question 17System Behavior

What does a generalization relationship between parent use case A and child use case B mean?

  1. The parent includes the child at a named extension point
  2. The child extends the parent only when its condition is true
  3. The child inherits the behavior and meaning of the parent and may add to it Correct answer.
  4. The parent and child execute concurrently

Explanation

Use case generalization works like classifier inheritance: the child use case shares the parent's behavior and intent and can specialize it. Unlike «include» and «extend», it adds no conditional insertion of behavior.

Question 18System Behavior

An interruptible activity region contains several running actions and one edge leading out of the region to a handler action. What happens when that edge's event occurs?

  1. The interrupting action runs concurrently with the region's actions
  2. The region's actions complete before the interrupting action begins
  3. The interrupt is ignored unless the region's final node has fired
  4. The actions still executing in the region are terminated and the interrupting action begins Correct answer.

Explanation

An interrupting edge aborts the tokens and actions within the interruptible region when it is taken, then passes control to the action outside the region. This lets a group of actions be abandoned as a unit when an exceptional event occurs.

Question 19System Behavior

How does a merge node differ from a decision node?

  1. A merge node copies its incoming token to every outgoing edge
  2. A merge node waits until tokens arrive on all incoming edges
  3. A merge node has several incoming edges and one outgoing edge and applies no guards Correct answer.
  4. A merge node can be used only with object flows

Explanation

A merge node is the inverse of a decision node: it accepts alternative paths and passes any arriving token onward without evaluating guards. A decision node, in contrast, has one incoming edge and uses guards to choose among outgoing edges.

Question 20System Behavior

For what purpose is an interaction use, shown as a frame labeled ref, placed in a sequence diagram?

  1. To define an additional lifeline inside the enclosing interaction
  2. To reuse another interaction within the current interaction Correct answer.
  3. To cancel the messages that follow it in the interaction
  4. To specify constraints on the ordering of messages

Explanation

An interaction use references an existing interaction so that its behavior is incorporated without redrawing it. Gate messages on the frame connect the referenced interaction to the lifelines of the enclosing one.

Question 21System Behavior

A state lists event e1 as deferred. What happens when e1 occurs while the object is in that state?

  1. The event is consumed and discarded immediately
  2. The event causes the state machine to reset to its initial state
  3. The event is saved and reconsidered when the object reaches a state in which it is not deferred Correct answer.
  4. The event triggers every internal transition of the state

Explanation

Deferring an event means that if it occurs in that state it is not consumed and is not discarded; it remains available in the event pool. It can then be handled once the object has moved to a state where it is no longer deferred.

Question 22System Behavior

A composite state has a shallow history pseudostate. When the composite state is re-entered through that pseudostate, where does the object resume?

  1. In the exact nested configuration it had when the composite state was last exited
  2. In the most recently active direct substate, whose own default entry then applies Correct answer.
  3. Always in the initial pseudostate of the region
  4. In the state that was active when the state machine was first created

Explanation

A shallow history pseudostate restores only the direct substate that was last active and then follows that substate's default entry if it is composite. Restoring the full nesting of states requires a deep history pseudostate.

Question 23System Behavior

In one run-to-completion step, two transitions are enabled from the same source state. What does the UML semantics say?

  1. Neither transition fires until a guard resolves the conflict
  2. Only one transition fires; which one is not determined by the semantics alone Correct answer.
  3. Both transitions fire and both target states are entered
  4. The transition without a trigger is preferred over the one with a trigger

Explanation

A state machine fires at most one transition out of a given state per run-to-completion step, so conflicting transitions cannot both be taken. The notation provides no implicit priority, so modellers must add guards or restructure the model if a specific choice is required.

Question 24System Behavior

In SysML, what does it mean when an activity parameter is stereotyped «continuous»?

  1. The parameter is excluded from the activity's object flows
  2. The parameter is sampled once when the activity starts
  3. The parameter's value may flow continuously while the activity executes Correct answer.
  4. The parameter value can change only when the activity completes

Explanation

SysML distinguishes «continuous» from «discrete» flow for parameters and other items, where «continuous» means values are available throughout the execution rather than in discrete increments. This supports modelling physical flows such as fuel or electrical power.

Question 25System Behavior

A combined fragment uses the ignore operator and names messages m1 and m2. How is the enclosed interaction interpreted?

  1. Messages m1 and m2 are deferred until the fragment completes
  2. Messages m1 and m2 are blocked and may not occur at all
  3. Only messages m1 and m2 are shown, and all other messages are omitted
  4. Messages m1 and m2 may occur but are omitted, while all other messages are shown Correct answer.

Explanation

The ignore operator filters the description: the named messages, and their occurrences, are left out of the shown interaction while everything else remains visible. The consider operator does the opposite by showing only the listed messages.

Question 26System Behavior

What is the purpose of an initial node in an activity diagram?

  1. It stores objects that several later actions will read.
  2. It is where execution starts, offering a control token on each outgoing edge. Correct answer.
  3. It selects one of several outgoing flows according to the guards written on them.
  4. It terminates the activity once a token reaches it.

Explanation

An initial node is a control node that starts the activity: when the activity begins, it offers a control token on every outgoing edge, so several flows may start concurrently. It carries no objects and holds no state.

Question 27System Behavior

Which activity node produces an output only after tokens have arrived on all of its incoming edges?

  1. Fork node
  2. Join node Correct answer.
  3. Decision node
  4. Merge node

Explanation

A join node synchronizes concurrent flows: it waits until a token is available on every incoming edge, then offers a single token on its outgoing edge. This is the standard way to bring parallel branches back together.

Question 28System Behavior

In a sequence diagram, what does the narrow vertical rectangle drawn over a lifeline represent?

  1. A state invariant that must hold for the object.
  2. A message that arrives at the object but is not handled.
  3. The time during which the object exists.
  4. The period while the object is executing a behavior or operation. Correct answer.

Explanation

The rectangle is an execution specification (activation): it marks the interval during which the object is performing a behavior, typically in response to a received message. Its top and bottom align with the start and completion of that execution.

Question 29System Behavior

Use case A has an include relationship to use case B. What does this state?

  1. A is a specialization of B that adds new behavior.
  2. A and B may each be performed on their own, with no ordering between them.
  3. B's behavior may be added to A at a defined extension point.
  4. Every execution of A necessarily performs B as part of its behavior. Correct answer.

Explanation

Include is a mandatory, factored-out behavior: the base use case always incorporates the included use case at the point defined in its flow. The included use case is not optional and is not a specialization of the base.

Question 30System Behavior

On a UML transition, when does the effect behavior execute?

  1. As soon as the trigger event occurs, before any guard is evaluated.
  2. After the target state has been entered and its entry action has run.
  3. Continuously while the source state is active.
  4. When the transition fires, after exiting the source and before entering the target. Correct answer.

Explanation

Firing a transition proceeds in order: exit the source state, execute the transition's effect, then enter the target state. The effect therefore runs after the source's exit action and before the target's entry action.

Question 31System Behavior

What does reaching a final state in a state machine signify?

  1. The object ignores all further events but keeps its current state.
  2. The object is destroyed and its state machine is removed.
  3. The state machine returns to its initial state and starts again.
  4. The region containing the final state has completed its behavior. Correct answer.

Explanation

A final state marks completion of the region that contains it; if it is the outermost region, the classifier's state machine has finished. It does not by itself imply destruction of the object or a restart.

Question 32System Behavior

A sequence diagram contains a combined fragment with operator opt, guard [x > 0], and a single message inside. What does this mean?

  1. The message is sent repeatedly while x > 0 holds.
  2. The message is always sent, and x > 0 is checked afterwards.
  3. The fragment has two alternatives, one where x > 0 and one where it does not.
  4. The message is sent at most once, and only when x > 0 holds. Correct answer.

Explanation

The opt operator defines optional behavior: the operand is executed at most once, and only if its guard is true at that point. If the guard is false, the operand is simply skipped.

Question 33System Behavior

What does a control flow edge between two actions carry?

  1. A signal that the receiving action must consume.
  2. An object of a classifier type.
  3. A reference to the enclosing activity's parameter.
  4. A control token that indicates the source action has finished. Correct answer.

Explanation

A control flow carries only a control token, which signals that the source node has completed so the target may start. Objects moving between actions travel on object flows instead.

Question 34System Behavior

A state S has an internal transition with trigger e and effect behavior B. Event e occurs while the object is in S. What happens?

  1. e is ignored because internal transitions have no effect behavior.
  2. B executes, and S's exit and entry actions do not run. Correct answer.
  3. S is exited, B executes, and S is entered again, running its exit and entry actions.
  4. B executes after S's exit action and before its entry action.

Explanation

An internal transition is handled entirely within the state: it executes its effect without leaving the state, so neither the exit action nor the entry action of S is invoked. This contrasts with a self-transition, which does exit and re-enter the state.

Question 35System Behavior

A transition from S to T is divided into segments by a junction pseudostate, with a guard on each outgoing segment. How is this interpreted?

  1. Each segment fires separately, consuming one event per segment.
  2. The junction is a shorthand for two independent decision nodes in series.
  3. They form a single compound transition that fires in one step. Correct answer.
  4. The junction behaves as an intermediate state that holds the token until a guard becomes true.

Explanation

A junction joins transition segments into one compound transition: all guards along a path are evaluated within the same step, and if a path of true guards exists the whole transition fires once, running the effects of the segments in order. It is not a state and does not wait.

Question 36System Behavior

What happens when a transition enters a terminate pseudostate?

  1. The object's exit actions for all active states are performed, then it stops.
  2. The innermost region returns to its initial state.
  3. The state machine stops immediately, without performing exit behaviors. Correct answer.
  4. The object enters a wait state until it receives a restart event.

Explanation

The terminate pseudostate ends the execution of the state machine at once; no exit actions of active states are executed. It models an abrupt end of the object's life rather than an orderly completion.

Question 37System Behavior

A transition is triggered by the event written as 'when (temperature > 100)'. What kind of event is this?

  1. A change event Correct answer.
  2. A signal event
  3. A time event
  4. A call event

Explanation

A change event is defined by a boolean condition; it occurs when that condition becomes true. The 'when' keyword introduces exactly this kind of event.

Question 38System Behavior

A transition out of state S is labeled 'after(5 s)'. When is the trigger generated?

  1. Five seconds after the last event the object received.
  2. Five seconds after the state machine started running.
  3. At a fixed absolute time recorded when the model was created.
  4. Five seconds after the object entered S. Correct answer.

Explanation

A relative time event of the form after(t) starts its timer when the source state is entered. The event occurs once the object has been in that state for the stated duration.

Question 39System Behavior

A combined fragment uses the operator loop with the iteration bounds (2, 5) and no guard. What does it specify?

  1. The operand executes twice and then the fragment is skipped.
  2. The operand executes until a message inside it is lost.
  3. The operand executes between two and five times inclusive. Correct answer.
  4. The operand executes exactly five times.

Explanation

The loop operator with bounds (min, max) means the operand is repeated at least min and at most max times. With (2, 5) the number of iterations lies between two and five.

Question 40System Behavior

A combined fragment uses the operator par with two operands. What ordering does this impose?

  1. Messages in different operands can interleave; order within each operand is kept. Correct answer.
  2. Messages in the two operands are interleaved in strict alternation.
  3. Only one of the operands is executed, chosen by their guards.
  4. All messages of the first operand must complete before any message of the second operand begins.

Explanation

The par operator denotes parallel merging of operands: the events inside each operand keep their relative order, but events from different operands may be interleaved in any way. No fixed ordering is imposed between the operands.

Question 41System Behavior

A combined fragment uses the operator break with guard [fail]. What happens if fail is true?

  1. The operand is skipped and the enclosing fragment continues normally.
  2. The operand runs and the remainder of the enclosing fragment is skipped. Correct answer.
  3. All lifelines appearing inside the operand are destroyed when the guard becomes true.
  4. The enclosing interaction is repeated from the beginning.

Explanation

The break operator models an exceptional exit: when its guard is true, the operand is executed and the rest of the enclosing interaction fragment is not. When the guard is false, the operand is skipped and the enclosing fragment continues.

Question 42System Behavior

A message labeled with the stereotype «create» points to a lifeline. What does it mean?

  1. The receiver lifeline starts to exist at that point in the interaction. Correct answer.
  2. A new interaction is started inside the receiver.
  3. The sender creates a copy of its own object.
  4. The receiver's constructor is called on an existing object.

Explanation

A create message marks the instant at which the receiver object comes into existence, so its lifeline begins below that message. Before this point the object does not participate in the interaction.

Question 43System Behavior

In a sequence diagram, a message that begins at a small filled circle at the diagram border and ends on a lifeline is what?

  1. A lost message, because its receiver is outside the model.
  2. A found message, sent from outside the modeled scope. Correct answer.
  3. A message that is deferred until the receiver is created.
  4. A reply message to an earlier asynchronous call.

Explanation

A found message has a known receiver but an unspecified sender, drawn as an arrow arriving from a filled circle at the edge of the diagram. It represents input originating outside the modeled scope.

Question 44System Behavior

How does a data store node differ from a central buffer node in an activity?

  1. A data store can hold only control tokens.
  2. A read from a data store leaves the tokens in place; a read from a central buffer removes them. Correct answer.
  3. A data store discards its tokens when the activity completes.
  4. A data store accepts tokens only from object flows of the same type as the activity's output.

Explanation

A data store is a persistent object node: taking data from it does not consume the stored values, so they can be read repeatedly. A central buffer instead holds tokens temporarily and removes them when they are taken.

Question 45System Behavior

What does a send signal action do when it executes?

  1. It waits until the target object accepts the signal before completing.
  2. It creates a signal instance, sends it to a target, and does not wait for a reply. Correct answer.
  3. It blocks the activity until the target object sends a reply.
  4. It calls an operation on the target and waits for its return value.

Explanation

Sending a signal is asynchronous: the action creates a signal instance and delivers it to the target, then completes without waiting for the receiver. Any response must be modeled separately, for example by a reception in the target.

Question 46System Behavior

How does the strict operator differ from the seq operator in a combined fragment?

  1. strict totally orders all events of the operands; seq only keeps the order within each operand. Correct answer.
  2. The two operators are equivalent, since strict is a deprecated synonym for seq.
  3. The seq operator imposes a total order, whereas the strict operator allows free interleaving between operands.
  4. The strict operator applies only to synchronous messages, whereas the seq operator applies to all messages.

Explanation

The seq operator defines weak sequencing: order is preserved inside each operand and for events on the same lifeline, but events on different lifelines from different operands may interleave. The strict operator instead forces a complete ordering of all events of the operands.

Question 47System Behavior

A combined fragment uses the operator critical around two messages. What does this guarantee?

  1. The events in the fragment cannot be interleaved with events outside it. Correct answer.
  2. The fragment's messages take priority over messages in other fragments.
  3. The messages are executed only if no other message is in flight anywhere in the model.
  4. The messages inside the fragment are retried whenever the receiver is busy.

Explanation

A critical region is atomic with respect to the rest of the interaction: nothing outside the fragment may be interleaved between the events it contains. Other events may occur before or after the region, but not in the middle of it.

Question 48System Behavior

While a transition effect is executing, a new event arrives for the same object. What does UML semantics require?

  1. The event is queued and dispatched after the current run-to-completion step. Correct answer.
  2. The current transition is abandoned and the new event is processed at once.
  3. The new event interrupts the effect, which resumes after the new transition.
  4. The new event is discarded because the object is busy.

Explanation

State machine execution proceeds in run-to-completion steps: once a transition has started, it runs to its end, including exit, effect, and entry behaviors, before another event is dispatched. Events arriving meanwhile wait in the event queue.

Question 49System Behavior

An expansion region has the mode keyword stream. What does this specify?

  1. Input and output elements flow through the region as they become available. Correct answer.
  2. The region repeats until its input collection is empty.
  3. The region runs once for all elements at the same time, using one thread of control per element.
  4. The region runs once per element, in the order the elements appear.

Explanation

In stream mode the region behaves like a pipeline: elements may enter and leave as soon as they are ready, with several elements in the region at once. This differs from iterative mode, which processes one element after another, and from parallel mode, which processes elements concurrently.

Question 50System Behavior

A local transition has a composite state as both its source and its target. How does it differ from an external self-transition on the same state?

  1. The local transition executes the composite state's entry action but not its exit action.
  2. The local transition fires only from the composite state's initial pseudostate.
  3. The local transition does not fire unless the composite state's regions are all inactive.
  4. It does not exit and re-enter the composite state, though substates may be re-entered. Correct answer.

Explanation

A local transition keeps the composite state active, so its exit and entry actions are not performed and its history is preserved. An external self-transition exits the composite state and re-enters it, running its exit and entry actions and restarting its regions.