The Unified Modeling Language User Guide

1
The Unified Modeling Language User Guide

• Chapter 23
• Time and Space

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Chapter 23 Topics

• Introduction
• Terms and Concepts
• Time
• Location

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Introduction

• Modeling time and space is a requirement for
  real-time and distributed systems.
• UML supports a number of features for modeling
  requirements unique to real-time and distributed
  systems.
• Real-time systems require precise timings in the
  sending and receiving of messages.
• Hard Real Time - Accurate performance to the
  millisecond or even nanosecond.
• Soft Real Time - Accurate performance to the
  second or longer.

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Introduction

• Distributed systems are made up of components
  spread out over multiple nodes.
• A node is a computational resource -- a computer.
• The nodes may be in the same box, or spread
  throughout a room, building, city, country, or
  the world.

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Introduction
6
Terms and Concepts

• Time
• Timing Mark - A denotation for the time at which
  an event occurs.
• Time Expression - An expression that evaluates to
  an absolute or relative value of time.
• Timing Constraint - A semantic statement about
  the absolute or relative value of time.

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Terms and Concepts
8
Terms and Concepts

• Location
• A component is a file (or collection of files)
  that reside on a node(s).
• In a non-distributed system all of the components
  reside on the same node.
• In a distributed system components are spread out
  over multiple nodes.
• Some components migrate from node to node over
  time.
• Some components appear in duplicate on multiple
  nodes.

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Terms and Concepts