ch 23 time and space

8/2/2019 CH 23 Time and Space

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CH 23: Time and SpaceBy

B.GokulR.Marshall

Ismath jafery


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Where you find time and space Behavioral things are the dynamic parts of UML models. These are

the verbs of a model, representing behavior over time and space. Inall, there are two primary kinds of behavioral things.

Time and space constraints, commonly used when modeling real

time systems. when you visualize states, you are really specifying the value ofits

state at a given moment in time and space. It's possible toshow the changing state of an object by showing it multipletimes in the same interaction diagram, but with each

occurrence representing a different state. In the real world, every computation takes some amount of

time and space. Especially for hard real time systems, it'simportant that you model these properties.


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Where you find time and space In the real world, things happen. Not only do

things happen, but lots of things may happen atthe same time, and at the most unexpected times.

"Things that happen" are called events, and eachone represents the specification of a significantoccurrence that has a location in time and space.

An event is the specification of a significantoccurrence that has a location in time and space


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What we will see today are Time, duration, and location

Modeling timing constraints

Modeling the distribution of objects Modeling objects that migrate

Dealing with real time and distributed

systems


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Timing Constraints and Location


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Common Modeling Techniques:Modeling Timing Constraints For each event in an interaction, consider whether it

must start at some absolute time.Model that real timeproperty as a timing constraint on the message.

For each interesting sequence of messages in aninteraction, consider whether there is an associatedmaximum relative time for that sequence. Model thatreal time property as a timing constraint on thesequence.

For each time critical operation in each class, considerits time complexity. Model those semantics as timingconstraints on the operation.


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Modeling Timing Constraint


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Modeling the Distribution of Objects Consider all its neighbors and their locations. A

tightly coupled locality will have neighboringobjects close by; a loosely coupled one will have

distant objects (and thus, there will be latency incommunicating with them). Tentatively allocateobjects closest to the actors that manipulate them.

Next consider patterns of interaction among related

sets of objects. Co-locate sets of objects that havehigh degrees of interaction, to reduce the cost ofcommunication. Partition sets of objects that havelow degrees of interaction.


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Modeling the Distribution of Objects Next consider the distribution of responsibilities across

the system. Redistribute your objects to balance theload of each node.

Consider also issues of security, volatility, and qualityof service, and redistribute your objects as appropriate.

Render this allocation in one of two ways:

1. By nesting objects in the nodes of a deploymentdiagram

2. By explicitly indicating the location of the objectas a tagged value


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Modeling the Distribution of Objects


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Modeling Objects that Migrate Select an underlying mechanism for physically

transporting objects across nodes.

Render the allocation of an object to a node by

explicitly indicating its location as a tagged value. Using the become and copy stereotyped messages,

render the allocation of an object to a new node.

Consider the issues of synchronization (keeping thestate of cloned objects consistent) and identity(preserving the name of the object as it moves).


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Modeling Objects that Migrate


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ch 23 time and space

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