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22 Cards in this Set
- Front
- Back
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state machine |
a model that shows how an object changes from state in response to events - uses statecharts as notations |
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state |
represent some condition or situation in the life of an object - it is not an action but a description of something about the object that will remain true until something happens |
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state machine diagrams consist |
- states: represented by the round-cornered rectangles - events: gives as labels on transition arrows - transitions: represented by arrows and idnetified by the events that give rise to them - transitions occur as a response to an event, and cause a change of state |
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guard [......] |
is used to choose which transition to take if the same event appears on more than one transition |
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transitions |
changes takes place in the system they are either fired or trigerred by events |
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the state machine models |
- the life history of a single object: - its initial state when first created - the different states it can be while it exists - how it can move from state to state in response to events - the state transitions that are possible |
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initial state |
it is not a true state, but is instead a way of indicating which of the real states he object will enter first |
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final state |
show that processing has been terminated. it has only one outgoing transition, whereas a final state can have many incoming transitions bu no outgoing transitions |
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actions |
consequences are recorded in the action part of the label on the transaction - event / action - a single event may often lead to a sequence of actions - if there were more messages to be sent, they could be added to the action sequence following the event - each action is separated from the next in the list by a semicolon |
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guards |
it is evaluated when an event occurs - the transition and any associated actions will only take place if the guard evaluates to true accept(aGuest) [reservation exist] / setOccupants(aGuest) ; aGuest.setRoom(self) |
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self- transition |
originates in one state and returns to the same state. - commonly found in state machines that model loops or cycles |
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avoid putting actions on every transition by using: |
- an entry event that is trigerred every time an object enters a state - an exit event that is trigerred every time an object leaves the state |
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internal transition |
- an event cause an object toreturn again to the same state but without performing the entry and exit events -used to handle an interrupt where you want some action to take place that does not affect the current state - they are written inside the state to which they refer |
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benefits of state machines |
- identifying which messages affect which attributes and considering the consequences for each onject belonging to a given class - they help understand the behaviour of an object over its lifetime - they help to understand how an object or system must respond to events, object interactions - they are ensuring correctness |
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state independent objects |
if the object always responds in the same way to a given event, it is unlikely that you need a state diagram |
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state dependent objects |
those objects that react differently. |
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packages |
a way of model elements into a unit - can be used to group almost everything - each package define a namespace - one package can be associated with another - a package can be depend on another package - they don't have interfaces and they cannot interact with each other |
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3 reasons to partition a system: |
- to manage size and complexty - for information hiding - for logical decomposition |
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representation of package structure |
- draw a package inside another - represent the package hierarchy in a tree structure |
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UML representation of package access |
- UML allows you to import the contents of one package into another - an alternative machanism is to use the stereotype << access >> |
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other use of packages |
- you can use packages to present different views of a software system such as its architecture |
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advantages of system separation into 3 layers |
- developers can be allocated to different layers to facilitate parallel development or the user of particular skills such as interface design - reuse becomes possible in certain areas |
