Recitation 8

1
Recitation 8

• Godfrey Tan

2
Administrivia

• Hand back Quiz 1 at end of section
• PS 4 due next Monday, March 11
• Use office hours, forum, zephry

3
Overview of 6.170

• Specs Needed to tell other people what our code
  does
• MDDs
• Reason about modularity and reuse
• Try to minimize dependencies
• OMs
• Reason about problems or the state of a program
• Useful in examining your data model or analyzing
  constraints of your system
• Testing Debugging
• ADTs
• Provides abstraction and way of solving problems
  by designing software that closely resembles the
  problem
• AF/RI
• Ability to reason locally about correctness
• AF ? transformation between a COM to a POM tells
  us how what we are coding
• RI ? properties and additional constraints for a
  COM tells us what should always hold about our
  data model
• Rep Independence and Rep Exposure

4
Graph Requirements

• Directed
• Multi-graph
• Dynamic add and remove nodes
• Flexible works for other applications

5
Graph Operations

• addNode, containsNode
• addEdge, containsEdge
• Traversal
• Predecessors, successors

6
Implementation

• Centralized
• Graph stores everything
• May or may not require Node class
• Distributed
• Graph stores Nodes
• Node stores Edges

7
Implementation

• Separate data and internal structures
• Do not expose nodes and edges
• Apps stores raw data associated with nodes and
  edges
• Combine data and basic structures
• Public Node and Edge classes
• Apps associate customized data by extending Node
  and Edge classes

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Centralized and Separate I

• Graph
• void addNode(Object nodeData)
• void addEdge(Object from, Object to, Object
  label)
• int containsNode(Object nodeData)
• int containsEdge(Object from, Object to)
• Iterator predecessors(Object node)
• Iterator successors(Object node)
• Iterator getNode()
• Iterator getLabel(Object from, Object to)

9
Centralized and Separate II

• Graph
• Handle addNode(Object nodeData)
• Handle addEdge(Object from, Object to, Object
  label)
• int containsNode(Handle node)
• int containsEdge(Handle edge)
• Iterator predecessors(Handle node)
• Iterator successors(Handle node)
• Iterator getNode()
• Iterator getLabel(Handle e)

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Distributed and combined

• Graph
• void addNode(Node o)
• boolean containsNode(Node o)
• boolean containsEdge(Edge e)
• Iterator predecessors(Node o)
• Iterator successors(Node o)
• Iterator getNode()
• Iterator getLabel(Edge e)

11
Distributed and combined

• Node
• Graph graph
• Edge addEdge(Node to, Object label)
• Iterator getInEdges()
• Iterator getOutEdges()
• Edge
• Node from, to Object label
• Node getFrom()
• Node getTo()
• Object getLabel() void setLabel(Object label)

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Problem Set 4

• More POMs
• AF (toString)
• RI (checkRep)
• Fixing your problems
• Testing

13
Quiz

• Avg 73.29744
• StdDev 12.79
• Other than minor fixes such as wrong addition,
  you must write a written request for re-grade.