Systems Analysis II Activity Diagrams

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Systems Analysis IIActivity Diagrams

• INFO 355
• Glenn Booker

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Activity Diagrams

• Activity Diagrams are a type of flowchart used to
  describe a business process or workflow
• They support parallel tasks, which a pure
  flowchart cant handle
• They are derived from state diagram notation, so
  dont be surprised by the similarities

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Scope of Activity Diagrams

• An activity diagram might show the logic for a
  complex use case (and all its extensions), or
  show the interaction among several use cases
  (such as when included use cases apply)
• An activity diagram can show the logical
  decisions of a process that the use case diagram
  cant show

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Activity Diagram Notation

• Activity diagram notation includes
• The processes to be performed, which appear as
  boxes with rounded corners
• The processes are connected by lines with arrows,
  to show the direction of process flow
• Arrows are always directional in an activity
  diagram
• Use the Guard field for conditions
• Decisions are shown by diamonds

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Activity Diagram Simple Example
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Decisions

• Notice that the diamond symbol is used to show a
  split in the process flow due to a decision
• And the same symbol is used to show when the
  process flows merge afterwards

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Concurrent Flow

• Notice the implied assumption of time going
  forward down the page
• Concurrent, or parallel flows can be shown by
  using a fork symbol when the flows split, and a
  join symbol when they reconnect

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Uses for Concurrent Flow

• Several parallel activities might take place
  after a single decision
• For example, approval of a release might initiate
  parallel activities to
• Prepare a release description
• Start packaging the release
• Notify customer of impending release
• Lock the contents of the release

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Concurrency Example
Shows four concurrent activity threads to prepare
for a new baseline release this might all be
part of a process called Prepare Release
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Partitions

• Notice that activities are often performed by
  different organizations within your project
• You could add the organization to the activity
  name, e.g. Program Control Notifies Customer
• Or use the approach on the next slide
• Here is another variation on the swimlane
  approach (each organization has its own lane)

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Partition Example
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Adding Details - Decomposing

• Each step in an activity diagram could correspond
  to (or be decomposed into) a process or procedure
  which is documented elsewhere
• For example, Prepare Release Description could
  follow a procedure to explain it in more detail

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Adding Details - Decomposing

• For that matter, the whole development process
  could be described in a single step, then broken
  down to any desired level of detail

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Adding Details - Decomposing
Which in turn becomes
Notice similarity to the project schedule (WBS)
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Adding Details - Decomposing

• Many CASE tools, such as the Rational suite, can
  directly support such a process decomposition

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Timing and Signals

• So far the sense of time has been pretty vague
• Time goes forward down the page
• Forks and joins indicate when concurrent
  processes collectively begin and end
• Decisions and merges reflect the start and end of
  conditional process paths
• To be more precise, use signals

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Signals

• A Time Signal can be used to indicate when a
  process waits for a specific timed event before
  it begins
• E.g. end of month to start generating a report
• The Time Signal is like an hourglass, labeled to
  show what event for which it waits
• (I made this one manually)

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Signals

• Send Signals are triggered by some process to
  start a timer
• Receive Signals accept a signal as input, and
  usually sound like an event more than a process
• Taxi arrives, Itinerary confirmed, etc.

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Signals

• A signal can be split by a fork symbol
• Fig 11.6, p. 123
• (Send and receivelabels overwrittenmanually)

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Tokens

• To help follow a process, it sometimes helps to
  imagine physical tokens being passed along the
  paths
• A fork creates two or more tokens to follow each
  path separately
• A join waits for all tokens to arrive before
  proceeding

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Other Activity Diagram Tricks

• There are lots of other things which can be shown
  on an activity diagram, most of which are very
  implementation-focused
• Hence, well ignore them here
• The last well consider is the join specification

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Join Specification

• A join specification is an explanation of the
  conditions needed for continuing
• Normally, simply having collected all tokens is
  enough
• A join specification is a Boolean expression in
  curly brackets
• joinSpec value of inserted coins gt price of
  selected drink