Class 32: Design Heuristics (4): Choosing Relationships

Held: Monday, 15 November 2004

Summary: Today we consider when (and when not) to make particular relationship choices.

Related Pages:

• EBoard.
• Riel's Heuristics.

Overview:

• Today's strategy
• Choosing a relationship
• Choosing how to get objects to use

Today's Strategy

• At the end of the last class, Ryan asked Okay, now how do we decide which form of 'uses' to use or which relationship to use?
• The answer, of course, is Heuristics!
• Riel has written some heuristics for us to use. Your challenge will be to figure out which ones apply. Keep your book or the handout handy.
• We may have to write some of our own.

Strategies for Selecting a Relationship

• We know of a variety of relationships:
  • Uses
  • Contains
  • Contains by association
  • Inherits
  • Creates
  • Associates in other ways
• What strategies suggest what relationships?
• Note that we may have to use uses and associates in other ways as defaults.

Strategies for Selecting a Use Relationship

• We know a variety of ways to obtain something to use:
  • Contain the thing
  • Contain the thing by association
  • Receive the thing as a parameter
  • Query an oracle to receive the thing
  • Refer to a very global variable
  • Create the thing
  • Permit an oracle to forward the request
• When should we use a particular strategy? When should we not use a particular strategy?